https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-14_Evaluation&feed=atom&action=history UFR 3-14 Evaluation - Revision history 2024-03-29T15:23:49Z Revision history for this page on the wiki MediaWiki 1.39.2 https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-14_Evaluation&diff=33575&oldid=prev Dave.Ellacott: Dave.Ellacott moved page SilverP:UFR 3-14 Evaluation to UFR 3-14 Evaluation over redirect 2017-02-12T13:22:02Z <p>Dave.Ellacott moved page <a href="/w/index.php/SilverP:UFR_3-14_Evaluation" class="mw-redirect" title="SilverP:UFR 3-14 Evaluation">SilverP:UFR 3-14 Evaluation</a> to <a href="/w/index.php/UFR_3-14_Evaluation" title="UFR 3-14 Evaluation">UFR 3-14 Evaluation</a> over redirect</p> <table style="background-color: #fff; color: #202122;" data-mw="interface"> <tr class="diff-title" lang="en"> <td colspan="1" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td> <td colspan="1" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 13:22, 12 February 2017</td> </tr><tr><td colspan="2" class="diff-notice" lang="en"><div class="mw-diff-empty">(No difference)</div> </td></tr></table> Dave.Ellacott https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-14_Evaluation&diff=11207&oldid=prev Niek.verhoeven at 19:23, 29 August 2009 2009-08-29T19:23:17Z <p></p> <table style="background-color: #fff; color: #202122;" data-mw="interface"> <col class="diff-marker" /> <col class="diff-content" /> <col class="diff-marker" /> <col class="diff-content" /> <tr class="diff-title" lang="en"> <td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td> <td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 19:23, 29 August 2009</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l101">Line 101:</td> <td colspan="2" class="diff-lineno">Line 101:</td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>{{UFR|front=UFR 3-14|description=UFR 3-14 Description|references=UFR 3-14 References|testcase=UFR 3-14 Test Case|evaluation=UFR 3-14 Evaluation|qualityreview=UFR 3-14 Quality Review|bestpractice=UFR 3-14 Best Practice Advice|relatedACs=UFR 3-14 Related ACs}}</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>{{UFR|front=UFR 3-14|description=UFR 3-14 Description|references=UFR 3-14 References|testcase=UFR 3-14 Test Case|evaluation=UFR 3-14 Evaluation|qualityreview=UFR 3-14 Quality Review|bestpractice=UFR 3-14 Best Practice Advice|relatedACs=UFR 3-14 Related ACs}}</div></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;"></del></div></td><td colspan="2" class="diff-side-added"></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;"></del></div></td><td colspan="2" class="diff-side-added"></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;">[[Category:Underlying Flow Regime]]</del></div></td><td colspan="2" class="diff-side-added"></td></tr> </table> Niek.verhoeven https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-14_Evaluation&diff=8510&oldid=prev Daveg: UFR 3-14 Evaluation moved to SilverP:UFR 3-14 Evaluation 2009-04-07T12:45:18Z <p><a href="/w/index.php/UFR_3-14_Evaluation" title="UFR 3-14 Evaluation">UFR 3-14 Evaluation</a> moved to <a href="/w/index.php/SilverP:UFR_3-14_Evaluation" class="mw-redirect" title="SilverP:UFR 3-14 Evaluation">SilverP:UFR 3-14 Evaluation</a></p> <table style="background-color: #fff; color: #202122;" data-mw="interface"> <tr class="diff-title" lang="en"> <td colspan="1" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td> <td colspan="1" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 12:45, 7 April 2009</td> </tr><tr><td colspan="2" class="diff-notice" lang="en"><div class="mw-diff-empty">(No difference)</div> </td></tr></table> Daveg https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-14_Evaluation&diff=5137&oldid=prev David.Fowler at 11:40, 12 March 2009 2009-03-12T11:40:59Z <p></p> <table style="background-color: #fff; color: #202122;" data-mw="interface"> <col class="diff-marker" /> <col class="diff-content" /> <col class="diff-marker" /> <col class="diff-content" /> <tr class="diff-title" lang="en"> <td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td> <td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 11:40, 12 March 2009</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l84">Line 84:</td> <td colspan="2" class="diff-lineno">Line 84:</td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[Image:U3-14d32_files_image009.jpg]]</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[Image:U3-14d32_files_image009.jpg]]</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|}</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|}</div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">&lt;br clear="ALL" /></ins></div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>&lt;u&gt;Figure 4.&lt;/u&gt; Comparison of mean cube surface pressures on the centre-plane, from Tsuchiya &amp;amp; Murakami (1997). Note that the MMK model is a variant of the LK modification to the standard ''k-&amp;epsilon;'' model and has very similar effects. The experiment is reported (very briefly) in Murakami ''et al'' (1990).</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>&lt;u&gt;Figure 4.&lt;/u&gt; Comparison of mean cube surface pressures on the centre-plane, from Tsuchiya &amp;amp; Murakami (1997). Note that the MMK model is a variant of the LK modification to the standard ''k-&amp;epsilon;'' model and has very similar effects. The experiment is reported (very briefly) in Murakami ''et al'' (1990).</div></td></tr> </table> David.Fowler https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-14_Evaluation&diff=5136&oldid=prev David.Fowler at 11:40, 12 March 2009 2009-03-12T11:40:16Z <p></p> <table style="background-color: #fff; color: #202122;" data-mw="interface"> <col class="diff-marker" /> <col class="diff-content" /> <col class="diff-marker" /> <col class="diff-content" /> <tr class="diff-title" lang="en"> <td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td> <td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 11:40, 12 March 2009</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l1">Line 1:</td> <td colspan="2" class="diff-lineno">Line 1:</td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;"></del></div></td><td colspan="2" class="diff-side-added"></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>{{UFR|front=UFR 3-14|description=UFR 3-14 Description|references=UFR 3-14 References|testcase=UFR 3-14 Test Case|evaluation=UFR 3-14 Evaluation|qualityreview=UFR 3-14 Quality Review|bestpractice=UFR 3-14 Best Practice Advice|relatedACs=UFR 3-14 Related ACs}}</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>{{UFR|front=UFR 3-14|description=UFR 3-14 Description|references=UFR 3-14 References|testcase=UFR 3-14 Test Case|evaluation=UFR 3-14 Evaluation|qualityreview=UFR 3-14 Quality Review|bestpractice=UFR 3-14 Best Practice Advice|relatedACs=UFR 3-14 Related ACs}}</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr> <tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l19">Line 19:</td> <td colspan="2" class="diff-lineno">Line 18:</td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Detailed comparisons are contained in the Rodi reports. These include centre-plane streamline plots, some velocity profiles both above and downstream of the cube and some of the global parameters like ''x&lt;sub&gt;F&lt;/sub&gt;'' and ''x&lt;sub&gt;R&lt;/sub&gt;'' (separation and attachment locations). Figures 2 and 3 are taken from Rodi (2002) and Rodi ''et al'' (1997), respectively, and compare streamline patterns and velocity profiles with different models.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Detailed comparisons are contained in the Rodi reports. These include centre-plane streamline plots, some velocity profiles both above and downstream of the cube and some of the global parameters like ''x&lt;sub&gt;F&lt;/sub&gt;'' and ''x&lt;sub&gt;R&lt;/sub&gt;'' (separation and attachment locations). Figures 2 and 3 are taken from Rodi (2002) and Rodi ''et al'' (1997), respectively, and compare streamline patterns and velocity profiles with different models.</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The LES solutions are generally significantly closer to the experimental results than ''k-<del style="font-weight: bold; text-decoration: none;">ε</del>'' solutions. The point is emphasised in Table 1, which shows separation and attachment locations. ''X&lt;sub&gt;T&lt;/sub&gt;'' is the location of shear layer attachment on the roof of the cube; the experimental evidence suggests that this does not occur so models which produce it are in that sense deficient. Notice that ''k-<del style="font-weight: bold; text-decoration: none;">ε</del>'' models, even those which use the KL modification, produce much too long a downstream separation region. In fact, the modified model actually leads to a worse prediction in this sense than the standard ''k-<del style="font-weight: bold; text-decoration: none;">ε</del>'' model.</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The LES solutions are generally significantly closer to the experimental results than ''k-<ins style="font-weight: bold; text-decoration: none;">&amp;epsilon;</ins>'' solutions. The point is emphasised in Table 1, which shows separation and attachment locations. ''X&lt;sub&gt;T&lt;/sub&gt;'' is the location of shear layer attachment on the roof of the cube; the experimental evidence suggests that this does not occur so models which produce it are in that sense deficient. Notice that ''k-<ins style="font-weight: bold; text-decoration: none;">&amp;epsilon;</ins>'' models, even those which use the KL modification, produce much too long a downstream separation region. In fact, the modified model actually leads to a worse prediction in this sense than the standard ''k-<ins style="font-weight: bold; text-decoration: none;">&amp;epsilon;</ins>'' model.</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>It is unfortunate that no comparisons between surface pressures are available from this workshop. However, in a paper from Murakami's group, Tsuchiya ''et al'' (1997) compared measured cube surface pressure distributions from another experiment (see §2 above) with various RANS computations and it appears that KL type modifications lead to quite good agreement between computation and experiment, see figure 4. But only minimal flow field data is shown and there is evidence that the computed length of the downwind separation region is no closer to the experimental result than was reported by Rodi for RANS computations. This seems not inconsistent with the 'inverse' of the point made by Shah &amp;amp; Ferziger (1997) (noted in §2 above), i.e. that adequate computation of the surface pressure field does not necessarily imply adequate computation of the velocity field. We repeat again here their statement that 'to validate a method solely by its ability to predict the velocity distribution about a single object is dangerous; relying on the pressure distribution alone is surely of no value whatever'. From a Wind Engineering perspective, one might sometimes be quite satisfied with adequate surface pressure computation (if one is only interested in forces) but clearly, if processes like pollutant dispersion in the wake or pedestrian winds around the building are of interest, then being confident about the surface pressure computations is evidently not enough to engender confidence about the flow field results.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>It is unfortunate that no comparisons between surface pressures are available from this workshop. However, in a paper from Murakami's group, Tsuchiya ''et al'' (1997) compared measured cube surface pressure distributions from another experiment (see §2 above) with various RANS computations and it appears that KL type modifications lead to quite good agreement between computation and experiment, see figure 4. But only minimal flow field data is shown and there is evidence that the computed length of the downwind separation region is no closer to the experimental result than was reported by Rodi for RANS computations. This seems not inconsistent with the 'inverse' of the point made by Shah &amp;amp; Ferziger (1997) (noted in §2 above), i.e. that adequate computation of the surface pressure field does not necessarily imply adequate computation of the velocity field. We repeat again here their statement that 'to validate a method solely by its ability to predict the velocity distribution about a single object is dangerous; relying on the pressure distribution alone is surely of no value whatever'. From a Wind Engineering perspective, one might sometimes be quite satisfied with adequate surface pressure computation (if one is only interested in forces) but clearly, if processes like pollutant dispersion in the wake or pedestrian winds around the building are of interest, then being confident about the surface pressure computations is evidently not enough to engender confidence about the flow field results.</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>{| border=&quot;1&quot;</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>{| border=&quot;1&quot;</div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">|+ &lt;u>Table 1&lt;/u>. Upstream separation point (''x&lt;sub>F&lt;/sub>''), top attachment point (''x&lt;sub>T&lt;/sub>'') and rear attachment point (''x&lt;sub>R&lt;/sub>'') from various turbulence models and compared with the experimental values.</ins></div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>! MODEL !! COMMENT !! ''x&lt;sub&gt;F&lt;/sub&gt;'' !! ''x&lt;sub&gt;T&lt;/sub&gt;'' !! ''x&lt;sub&gt;R&lt;/sub&gt;''</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>! MODEL !! COMMENT !! ''x&lt;sub&gt;F&lt;/sub&gt;'' !! ''x&lt;sub&gt;T&lt;/sub&gt;'' !! ''x&lt;sub&gt;R&lt;/sub&gt;''</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|-</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|-</div></td></tr> <tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l36">Line 36:</td> <td colspan="2" class="diff-lineno">Line 36:</td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>| LES (IIS-KOBA) || Smagorinsky (short averaging) || 0.835 || 0.814 || 1.652</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>| LES (IIS-KOBA) || Smagorinsky (short averaging) || 0.835 || 0.814 || 1.652</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|-  </div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|-  </div></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>| RANS (''k-<del style="font-weight: bold; text-decoration: none;">ε</del>'') || Standard model || 0.651 || 0.432 || 2.182</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>| RANS (''k-<ins style="font-weight: bold; text-decoration: none;">&amp;epsilon;</ins>'') || Standard model || 0.651 || 0.432 || 2.182</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|-  </div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|-  </div></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>| RANS (''k-<del style="font-weight: bold; text-decoration: none;">ε</del>'') || KL modification || 0.650 || || 2.728</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>| RANS (''k-<ins style="font-weight: bold; text-decoration: none;">&amp;epsilon;</ins>'') || KL modification || 0.650 || || 2.728</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|-  </div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|-  </div></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>| RANS (''k-<del style="font-weight: bold; text-decoration: none;">ε</del>'') || Two-layer model || 0.950 || || 2.731</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>| RANS (''k-<ins style="font-weight: bold; text-decoration: none;">&amp;epsilon;</ins>'') || Two-layer model || 0.950 || || 2.731</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|-  </div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|-  </div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>| RANS (v&lt;sup&gt;2&lt;/sup&gt;-f) || Unsteady computation (Durbin) || 0.732 || || 1.876</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>| RANS (v&lt;sup&gt;2&lt;/sup&gt;-f) || Unsteady computation (Durbin) || 0.732 || || 1.876</div></td></tr> <tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l49">Line 49:</td> <td colspan="2" class="diff-lineno">Line 49:</td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|}</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|}</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;">&lt;u&gt;Table 1&lt;/u&gt;. Upstream separation point (''x&lt;sub&gt;F&lt;/sub&gt;''), top attachment point (''x&lt;sub&gt;T&lt;/sub&gt;'') and rear attachment point (''x&lt;sub&gt;R&lt;/sub&gt;'') from various turbulence models and compared with the experimental values.</del>&lt;br style=&quot;page-break-before: always&quot; clear=&quot;all&quot; /&gt;</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>&lt;br style=&quot;page-break-before: always&quot; clear=&quot;all&quot; /&gt;</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>{| align=&quot;left&quot;</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>{| align=&quot;left&quot;</div></td></tr> <tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l83">Line 83:</td> <td colspan="2" class="diff-lineno">Line 85:</td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|}</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>|}</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>&lt;u&gt;Figure 4.&lt;/u&gt; Comparison of mean cube surface pressures on the centre-plane, from Tsuchiya &amp;amp; Murakami (1997). Note that the MMK model is a variant of the LK modification to the standard ''k-<del style="font-weight: bold; text-decoration: none;">''''ε</del>'' model and has very similar effects. The experiment is reported (very briefly) in Murakami ''et al'' (1990).</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>&lt;u&gt;Figure 4.&lt;/u&gt; Comparison of mean cube surface pressures on the centre-plane, from Tsuchiya &amp;amp; Murakami (1997). Note that the MMK model is a variant of the LK modification to the standard ''k-<ins style="font-weight: bold; text-decoration: none;">&amp;epsilon;</ins>'' model and has very similar effects. The experiment is reported (very briefly) in Murakami ''et al'' (1990).</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>It is worth mentioning that a few workers have been able to employ &lt;u&gt;unsteady&lt;/u&gt; RANS methods to obtain more satisfactory results. Iaccarino &amp;amp; Durbin (2000), for example, have used Durbin's (1995) [[Image:U3-14d32_files_image012.gif]] turbulence model in an unsteady computation of the cube-in-a-channel problem and obtained very good agreement with the steady flow field found in the experiments. Data for this calculation are included in Table 1. No pressure comparisons were made, however. Note that a steady computation with the same model yielded results as bad as found in the other (''k-<del style="font-weight: bold; text-decoration: none;">ε</del>''-based) RANS computations. One of the reasons that LES does so much better for this problem is that some quasi-periodic shedding of vorticity from the side walls of the cube is observed in experiments. This enhances the exchange of momentum in the wake, thus reducing the length of the separated region. Steady RANS methods cannot account for this process, but this feature of the flow may be one of the reasons why the unsteady RANS solution of Iaccarino &amp;amp; Durbin does so much better. As might be expected from this argument, it should be noted that higher order (steady) RANS closures, like algebraic stress closures or full differential second-moment closures, fare no better than the simpler eddy-viscosity closures in predicting the downwind flow field (as shown by Murakami &amp;amp; Mochida, 1999, for example).</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>It is worth mentioning that a few workers have been able to employ &lt;u&gt;unsteady&lt;/u&gt; RANS methods to obtain more satisfactory results. Iaccarino &amp;amp; Durbin (2000), for example, have used Durbin's (1995) [[Image:U3-14d32_files_image012.gif]] turbulence model in an unsteady computation of the cube-in-a-channel problem and obtained very good agreement with the steady flow field found in the experiments. Data for this calculation are included in Table 1. No pressure comparisons were made, however. Note that a steady computation with the same model yielded results as bad as found in the other (''k-<ins style="font-weight: bold; text-decoration: none;">&amp;epsilon;</ins>''-based) RANS computations. One of the reasons that LES does so much better for this problem is that some quasi-periodic shedding of vorticity from the side walls of the cube is observed in experiments. This enhances the exchange of momentum in the wake, thus reducing the length of the separated region. Steady RANS methods cannot account for this process, but this feature of the flow may be one of the reasons why the unsteady RANS solution of Iaccarino &amp;amp; Durbin does so much better. As might be expected from this argument, it should be noted that higher order (steady) RANS closures, like algebraic stress closures or full differential second-moment closures, fare no better than the simpler eddy-viscosity closures in predicting the downwind flow field (as shown by Murakami &amp;amp; Mochida, 1999, for example).</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>It should also be noted that it is unclear to what extent the fairly ubiquitous use of standard wall functions in nearly all the computations may have degraded the accuracy of the computations. It is well known that in strongly adverse pressure gradient regions (i.e. near separation) and certainly within separated regions, the 'classic' log-law relationship for mean velocity does not hold. Wall functions cannot, therefore, capture the appropriate physics of the near-wall region. But in flows, like this one, where the global parameters are dominated by the influence of the unsteady, large eddy motions, it could be argued that the precise nature of the wall condition is not likely to be too critical. As yet, however, there is little proof of this assertion.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>It should also be noted that it is unclear to what extent the fairly ubiquitous use of standard wall functions in nearly all the computations may have degraded the accuracy of the computations. It is well known that in strongly adverse pressure gradient regions (i.e. near separation) and certainly within separated regions, the 'classic' log-law relationship for mean velocity does not hold. Wall functions cannot, therefore, capture the appropriate physics of the near-wall region. But in flows, like this one, where the global parameters are dominated by the influence of the unsteady, large eddy motions, it could be argued that the precise nature of the wall condition is not likely to be too critical. As yet, however, there is little proof of this assertion.</div></td></tr> </table> David.Fowler https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-14_Evaluation&diff=4043&oldid=prev David.Fowler: /* Comparison of CFD calculations with Experiments */ 2009-03-08T12:14:07Z <p><span dir="auto"><span class="autocomment">Comparison of CFD calculations with Experiments</span></span></p> <a href="//kbwiki.ercoftac.org/w/index.php?title=UFR_3-14_Evaluation&amp;diff=4043&amp;oldid=4038">Show changes</a> David.Fowler https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-14_Evaluation&diff=4038&oldid=prev David.Fowler: /* Comparison of CFD calculations with Experiments */ 2009-03-08T11:47:12Z <p><span dir="auto"><span class="autocomment">Comparison of CFD calculations with Experiments</span></span></p> <table style="background-color: #fff; color: #202122;" data-mw="interface"> <col class="diff-marker" /> <col class="diff-content" /> <col class="diff-marker" /> <col class="diff-content" /> <tr class="diff-title" lang="en"> <td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td> <td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 11:47, 8 March 2009</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l19">Line 19:</td> <td colspan="2" class="diff-lineno">Line 19:</td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Detailed comparisons are contained in the Rodi reports. These include centre-plane streamline plots, some velocity profiles both above and downstream of the cube and some of the global parameters like ''x&lt;sub&gt;F&lt;/sub&gt;'' and ''x&lt;sub&gt;R&lt;/sub&gt;'' (separation and attachment locations). Figures 2 and 3 are taken from Rodi (2002) and Rodi ''et al'' (1997), respectively, and compare streamline patterns and velocity profiles with different models.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Detailed comparisons are contained in the Rodi reports. These include centre-plane streamline plots, some velocity profiles both above and downstream of the cube and some of the global parameters like ''x&lt;sub&gt;F&lt;/sub&gt;'' and ''x&lt;sub&gt;R&lt;/sub&gt;'' (separation and attachment locations). Figures 2 and 3 are taken from Rodi (2002) and Rodi ''et al'' (1997), respectively, and compare streamline patterns and velocity profiles with different models.</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The LES solutions are generally significantly closer to the experimental results than ''k-<del style="font-weight: bold; text-decoration: none;">''''</del>ε'' solutions. The point is emphasised in Table 1, which shows separation and attachment locations. ''X&lt;sub&gt;T&lt;/sub&gt;'' is the location of shear layer attachment on the roof of the cube; the experimental evidence suggests that this does not occur so models which produce it are in that sense deficient. Notice that ''k-<del style="font-weight: bold; text-decoration: none;">''''</del>ε'' models, even those which use the KL modification, produce much too long a downstream separation region. In fact, the modified model actually leads to a worse prediction in this sense than the standard ''k-<del style="font-weight: bold; text-decoration: none;">''''</del>ε'' model.</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The LES solutions are generally significantly closer to the experimental results than ''k-ε'' solutions. The point is emphasised in Table 1, which shows separation and attachment locations. ''X&lt;sub&gt;T&lt;/sub&gt;'' is the location of shear layer attachment on the roof of the cube; the experimental evidence suggests that this does not occur so models which produce it are in that sense deficient. Notice that ''k-ε'' models, even those which use the KL modification, produce much too long a downstream separation region. In fact, the modified model actually leads to a worse prediction in this sense than the standard ''k-ε'' model.</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>It is unfortunate that no comparisons between surface pressures are available from this workshop. However, in a paper from Murakami's group, Tsuchiya ''et al'' (1997) compared measured cube surface pressure distributions from another experiment (see §2 above) with various RANS computations and it appears that KL type modifications lead to quite good agreement between computation and experiment, see figure 4. But only minimal flow field data is shown and there is evidence that the computed length of the downwind separation region is no closer to the experimental result than was reported by Rodi for RANS computations. This seems not inconsistent with the 'inverse' of the point made by Shah &amp;amp; Ferziger (1997) (noted in §2 above), i.e. that adequate computation of the surface pressure field does not necessarily imply adequate computation of the velocity field. We repeat again here their statement that 'to validate a method solely by its ability to predict the velocity distribution about a single object is dangerous; relying on the pressure distribution alone is surely of no value whatever'. From a Wind Engineering perspective, one might sometimes be quite satisfied with adequate surface pressure computation (if one is only interested in forces) but clearly, if processes like pollutant dispersion in the wake or pedestrian winds around the building are of interest, then being confident about the surface pressure computations is evidently not enough to engender confidence about the flow field results.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>It is unfortunate that no comparisons between surface pressures are available from this workshop. However, in a paper from Murakami's group, Tsuchiya ''et al'' (1997) compared measured cube surface pressure distributions from another experiment (see §2 above) with various RANS computations and it appears that KL type modifications lead to quite good agreement between computation and experiment, see figure 4. But only minimal flow field data is shown and there is evidence that the computed length of the downwind separation region is no closer to the experimental result than was reported by Rodi for RANS computations. This seems not inconsistent with the 'inverse' of the point made by Shah &amp;amp; Ferziger (1997) (noted in §2 above), i.e. that adequate computation of the surface pressure field does not necessarily imply adequate computation of the velocity field. We repeat again here their statement that 'to validate a method solely by its ability to predict the velocity distribution about a single object is dangerous; relying on the pressure distribution alone is surely of no value whatever'. From a Wind Engineering perspective, one might sometimes be quite satisfied with adequate surface pressure computation (if one is only interested in forces) but clearly, if processes like pollutant dispersion in the wake or pedestrian winds around the building are of interest, then being confident about the surface pressure computations is evidently not enough to engender confidence about the flow field results.</div></td></tr> </table> David.Fowler https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-14_Evaluation&diff=3467&oldid=prev David.Fowler: New page: {{UFR|front=UFR 3-14|description=UFR 3-14 Description|references=UFR 3-14 References|testcase=UFR 3-14 Test Case|evaluation=UFR 3-14 Evaluation|qualityreview=UFR 3-14 Quality Review|bestp... 2009-03-06T14:54:04Z <p>New page: {{UFR|front=UFR 3-14|description=UFR 3-14 Description|references=UFR 3-14 References|testcase=UFR 3-14 Test Case|evaluation=UFR 3-14 Evaluation|qualityreview=UFR 3-14 Quality Review|bestp...</p> <p><b>New page</b></p><div><br /> {{UFR|front=UFR 3-14|description=UFR 3-14 Description|references=UFR 3-14 References|testcase=UFR 3-14 Test Case|evaluation=UFR 3-14 Evaluation|qualityreview=UFR 3-14 Quality Review|bestpractice=UFR 3-14 Best Practice Advice|relatedACs=UFR 3-14 Related ACs}}<br /> <br /> <br /> {{Status|checked=no|by= |date= }}<br /> <br /> <br /> <br /> = Flow over surface-mounted cube/rectangular obstacles&lt;br /&gt; =<br /> <br /> Underlying Flow Regime 3-14 &lt;font size=&quot;-2&quot; color=&quot;#888888&quot;&gt;               © copyright ERCOFTAC 2004&lt;/font&gt;<br /> <br /> <br /> <br /> = Evaluation =<br /> <br /> == Comparison of CFD calculations with Experiments ==<br /> <br /> Detailed comparisons are contained in the Rodi reports. These include centre-plane streamline plots, some velocity profiles both above and downstream of the cube and some of the global parameters like ''x&lt;sub&gt;F&lt;/sub&gt;'' and ''x&lt;sub&gt;R&lt;/sub&gt;'' (separation and attachment locations). Figures 2 and 3 are taken from Rodi (2002) and Rodi ''et al'' (1997), respectively, and compare streamline patterns and velocity profiles with different models.<br /> <br /> The LES solutions are generally significantly closer to the experimental results than ''k-''''ε'' solutions. The point is emphasised in Table 1, which shows separation and attachment locations. ''X&lt;sub&gt;T&lt;/sub&gt;'' is the location of shear layer attachment on the roof of the cube; the experimental evidence suggests that this does not occur so models which produce it are in that sense deficient. Notice that ''k-''''ε'' models, even those which use the KL modification, produce much too long a downstream separation region. In fact, the modified model actually leads to a worse prediction in this sense than the standard ''k-''''ε'' model.<br /> <br /> It is unfortunate that no comparisons between surface pressures are available from this workshop. However, in a paper from Murakami's group, Tsuchiya ''et al'' (1997) compared measured cube surface pressure distributions from another experiment (see §2 above) with various RANS computations and it appears that KL type modifications lead to quite good agreement between computation and experiment, see figure 4. But only minimal flow field data is shown and there is evidence that the computed length of the downwind separation region is no closer to the experimental result than was reported by Rodi for RANS computations. This seems not inconsistent with the 'inverse' of the point made by Shah &amp;amp; Ferziger (1997) (noted in §2 above), i.e. that adequate computation of the surface pressure field does not necessarily imply adequate computation of the velocity field. We repeat again here their statement that 'to validate a method solely by its ability to predict the velocity distribution about a single object is dangerous; relying on the pressure distribution alone is surely of no value whatever'. From a Wind Engineering perspective, one might sometimes be quite satisfied with adequate surface pressure computation (if one is only interested in forces) but clearly, if processes like pollutant dispersion in the wake or pedestrian winds around the building are of interest, then being confident about the surface pressure computations is evidently not enough to engender confidence about the flow field results.<br /> <br /> {| style=&quot;margin-left: 32.4pt; border-collapse: collapse; border: none&quot; border=&quot;1&quot;<br /> | style=&quot;width: 117.0pt; border: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt&quot; width=&quot;156&quot; valign=&quot;top&quot; |<br /> &lt;center&gt;MODEL&lt;/center&gt;<br /> | style=&quot;width: 162.0pt; border: solid windowtext 1.0pt; border-left: none; padding: 0cm 5.4pt 0cm 5.4pt&quot; width=&quot;216&quot; valign=&quot;top&quot; |<br /> &lt;center&gt;COMMENT&lt;/center&gt;<br /> | style=&quot;width: 67.5pt; border: solid windowtext 1.0pt; border-left: none; padding: 0cm 5.4pt 0cm 5.4pt&quot; width=&quot;90&quot; valign=&quot;top&quot; |<br /> &lt;center&gt;''x&lt;sub&gt;F&lt;/sub&gt;''&lt;/center&gt;<br /> | style=&quot;width: 63.0pt; border: solid windowtext 1.0pt; border-left: none; padding: 0cm 5.4pt 0cm 5.4pt&quot; width=&quot;84&quot; valign=&quot;top&quot; |<br /> &lt;center&gt;''x&lt;sub&gt;T&lt;/sub&gt;''&lt;/center&gt;<br /> | style=&quot;width: 64.35pt; border: solid windowtext 1.0pt; border-left: none; padding: 0cm 5.4pt 0cm 5.4pt&quot; width=&quot;86&quot; valign=&quot;top&quot; |<br /> &lt;center&gt;''x&lt;sub&gt;R&lt;/sub&gt;''&lt;/center&gt;<br /> |-<br /> | style=&quot;width: 117.0pt; border: solid windowtext 1.0pt; border-top: none; padding: 0cm 5.4pt 0cm 5.4pt&quot; width=&quot;156&quot; valign=&quot;top&quot; |<br /> Experiment<br /> <br /> LES (UKAHY3)<br /> <br /> LES (UKAHY4)<br /> <br /> LES (UBWM2)<br /> <br /> LES (IIS-KOBA)<br /> <br /> RANS (''k-''''ε''&lt;span lang=&quot;EN-US&quot;&gt;&lt;font face=&quot;Symbol&quot;&gt;)&lt;/font&gt;&lt;/span&gt;<br /> <br /> RANS (''k-''''ε''&lt;span lang=&quot;EN-US&quot;&gt;&lt;font face=&quot;Symbol&quot;&gt;)&lt;/font&gt;&lt;/span&gt;<br /> <br /> RANS (''k-''''ε''&lt;span lang=&quot;EN-US&quot;&gt;&lt;font face=&quot;Symbol&quot;&gt;)&lt;/font&gt;&lt;/span&gt;<br /> <br /> RANS (v&lt;sup&gt;2&lt;/sup&gt;-f)<br /> <br /> RANS (v&lt;sup&gt;2&lt;/sup&gt;-f)<br /> | style=&quot;width: 162.0pt; border-top: none; border-left: none; border-bottom: solid windowtext 1.0pt; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt&quot; width=&quot;216&quot; valign=&quot;top&quot; |<br /> <br /> Martinuzzi &amp;amp; Tropea (1993)<br /> <br /> Smagorinsky sub-grid model<br /> <br /> Dynamic sub-grid model<br /> <br /> Samgorinsky<br /> <br /> Smagorinsky (short averaging)<br /> <br /> Standard model<br /> <br /> KL modification<br /> <br /> Two-layer model<br /> <br /> Unsteady computation (Durbin)<br /> <br /> Steady (Durbin)<br /> | style=&quot;width: 67.5pt; border-top: none; border-left: none; border-bottom: solid windowtext 1.0pt; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt&quot; width=&quot;90&quot; valign=&quot;top&quot; |<br /> &lt;center&gt; &lt;/center&gt;<br /> <br /> &lt;center&gt;1.040&lt;/center&gt;<br /> <br /> &lt;center&gt;1.287&lt;/center&gt;<br /> <br /> &lt;center&gt;0.998&lt;/center&gt;<br /> <br /> &lt;center&gt;0.808&lt;/center&gt;<br /> <br /> &lt;center&gt;0.835&lt;/center&gt;<br /> <br /> &lt;center&gt;0.651&lt;/center&gt;<br /> <br /> &lt;center&gt;0.650&lt;/center&gt;<br /> <br /> &lt;center&gt;0.950&lt;/center&gt;<br /> <br /> &lt;center&gt;0.732&lt;/center&gt;<br /> <br /> &lt;center&gt;0.640&lt;/center&gt;<br /> | style=&quot;width: 63.0pt; border-top: none; border-left: none; border-bottom: solid windowtext 1.0pt; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt&quot; width=&quot;84&quot; valign=&quot;top&quot; |<br /> &lt;center&gt; &lt;/center&gt;<br /> <br /> &lt;center&gt; &lt;/center&gt;<br /> <br /> &lt;center&gt; &lt;/center&gt;<br /> <br /> &lt;center&gt; &lt;/center&gt;<br /> <br /> &lt;center&gt;0.837&lt;/center&gt;<br /> <br /> &lt;center&gt;0.814&lt;/center&gt;<br /> <br /> &lt;center&gt;0.432&lt;/center&gt;<br /> | style=&quot;width: 64.35pt; border-top: none; border-left: none; border-bottom: solid windowtext 1.0pt; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt&quot; width=&quot;86&quot; valign=&quot;top&quot; |<br /> &lt;center&gt; &lt;/center&gt;<br /> <br /> &lt;center&gt;1.612&lt;/center&gt;<br /> <br /> &lt;center&gt;1.696&lt;/center&gt;<br /> <br /> &lt;center&gt;1.432&lt;/center&gt;<br /> <br /> &lt;center&gt;1.722&lt;/center&gt;<br /> <br /> &lt;center&gt;1.652&lt;/center&gt;<br /> <br /> &lt;center&gt;2.182&lt;/center&gt;<br /> <br /> &lt;center&gt;2.728&lt;/center&gt;<br /> <br /> &lt;center&gt;2.731&lt;/center&gt;<br /> <br /> &lt;center&gt;1.876&lt;/center&gt;<br /> <br /> &lt;center&gt;3.315&lt;/center&gt;<br /> <br /> &lt;center&gt; &lt;/center&gt;<br /> |}<br /> <br /> &lt;u&gt;Table 1&lt;/u&gt;. Upstream separation point (''x&lt;sub&gt;F&lt;/sub&gt;''), top attachment point (''x&lt;sub&gt;T&lt;/sub&gt;'') and rear attachment point (''x&lt;sub&gt;R&lt;/sub&gt;'') from various turbulence models and compared with the experimental values.&lt;br style=&quot;page-break-before: always&quot; clear=&quot;all&quot; /&gt;<br /> <br /> {| align=&quot;left&quot;<br /> | width=&quot;64&quot; height=&quot;10&quot; |<br /> |-<br /> |<br /> |<br /> [[Image:U3-14d32_files_image005.jpg]]<br /> |}<br /> <br /> &lt;br clear=&quot;ALL&quot; /&gt;<br /> <br /> &lt;u&gt;Figure 2.&lt;/u&gt; Mean flow streamlines on the centre-plane (left) and near the channel floor (right). Model notation as in Table 1.<br /> <br /> {| align=&quot;left&quot;<br /> | width=&quot;66&quot; height=&quot;9&quot; |<br /> |-<br /> |<br /> |<br /> [[Image:U3-14d32_files_image007.jpg]]<br /> |}<br /> <br /> &lt;br clear=&quot;ALL&quot; /&gt;<br /> <br /> &lt;u&gt;Figure 3.&lt;/u&gt; Mean (centre-plane) velocity profiles over the centre of the cube (a) and in the wake (b). Notation as in Table 1.<br /> <br /> {| align=&quot;left&quot;<br /> | width=&quot;163&quot; |<br /> |-<br /> |<br /> |<br /> [[Image:U3-14d32_files_image009.jpg]]<br /> |}<br /> <br /> &lt;u&gt;Figure 4.&lt;/u&gt; Comparison of mean cube surface pressures on the centre-plane, from Tsuchiya &amp;amp; Murakami (1997). Note that the MMK model is a variant of the LK modification to the standard ''k-''''ε'' model and has very similar effects. The experiment is reported (very briefly) in Murakami ''et al'' (1990).<br /> <br /> It is worth mentioning that a few workers have been able to employ &lt;u&gt;unsteady&lt;/u&gt; RANS methods to obtain more satisfactory results. Iaccarino &amp;amp; Durbin (2000), for example, have used Durbin's (1995) [[Image:U3-14d32_files_image012.gif]] turbulence model in an unsteady computation of the cube-in-a-channel problem and obtained very good agreement with the steady flow field found in the experiments. Data for this calculation are included in Table 1. No pressure comparisons were made, however. Note that a steady computation with the same model yielded results as bad as found in the other (''k-ε''-based) RANS computations. One of the reasons that LES does so much better for this problem is that some quasi-periodic shedding of vorticity from the side walls of the cube is observed in experiments. This enhances the exchange of momentum in the wake, thus reducing the length of the separated region. Steady RANS methods cannot account for this process, but this feature of the flow may be one of the reasons why the unsteady RANS solution of Iaccarino &amp;amp; Durbin does so much better. As might be expected from this argument, it should be noted that higher order (steady) RANS closures, like algebraic stress closures or full differential second-moment closures, fare no better than the simpler eddy-viscosity closures in predicting the downwind flow field (as shown by Murakami &amp;amp; Mochida, 1999, for example).<br /> <br /> It should also be noted that it is unclear to what extent the fairly ubiquitous use of standard wall functions in nearly all the computations may have degraded the accuracy of the computations. It is well known that in strongly adverse pressure gradient regions (i.e. near separation) and certainly within separated regions, the 'classic' log-law relationship for mean velocity does not hold. Wall functions cannot, therefore, capture the appropriate physics of the near-wall region. But in flows, like this one, where the global parameters are dominated by the influence of the unsteady, large eddy motions, it could be argued that the precise nature of the wall condition is not likely to be too critical. As yet, however, there is little proof of this assertion.<br /> <br /> &lt;font size=&quot;-2&quot; color=&quot;#888888&quot;&gt;© copyright ERCOFTAC 2004&lt;/font&gt;&lt;br /&gt;<br /> ----<br /> <br /> <br /> Contributors: Ian Castro - University of Southampton<br /> <br /> <br /> {{UFR|front=UFR 3-14|description=UFR 3-14 Description|references=UFR 3-14 References|testcase=UFR 3-14 Test Case|evaluation=UFR 3-14 Evaluation|qualityreview=UFR 3-14 Quality Review|bestpractice=UFR 3-14 Best Practice Advice|relatedACs=UFR 3-14 Related ACs}}<br /> <br /> <br /> [[Category:Underlying Flow Regime]]</div> David.Fowler