https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-12_Description&feed=atom&action=history UFR 3-12 Description - Revision history 2024-03-28T21:21:55Z Revision history for this page on the wiki MediaWiki 1.39.2 https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-12_Description&diff=33525&oldid=prev Dave.Ellacott: Dave.Ellacott moved page Silver:UFR 3-12 Description to UFR 3-12 Description over redirect 2017-02-12T13:14:21Z <p>Dave.Ellacott moved page <a href="/w/index.php/Silver:UFR_3-12_Description" class="mw-redirect" title="Silver:UFR 3-12 Description">Silver:UFR 3-12 Description</a> to <a href="/w/index.php/UFR_3-12_Description" title="UFR 3-12 Description">UFR 3-12 Description</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 13:14, 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_3-12_Description&diff=21794&oldid=prev Dave.Ellacott: /* Turbulent Kinetic Energy Modifications */ 2011-09-25T12:54:31Z <p><span dir="auto"><span class="autocomment">Turbulent Kinetic Energy Modifications</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 12:54, 25 September 2011</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l100">Line 100:</td> <td colspan="2" class="diff-lineno">Line 100:</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>The production rate of k, or also turbulent energy, is the work done by the mean strain rate against the turbulent stresses. It can also be expressed as: -uv &amp;times; (&amp;part;U/&amp;part;y) = (shear stress) &amp;times; (mean velocity gradient). The destruction rate on the other hand, is equal to &amp;epsilon;/T, where T is the turbulent time scale which is proportional to k/&amp;epsilon; and &amp;epsilon; is the rate at which the turbulent energy is dissipated by viscosity.</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>The production rate of k, or also turbulent energy, is the work done by the mean strain rate against the turbulent stresses. It can also be expressed as: -uv &amp;times; (&amp;part;U/&amp;part;y) = (shear stress) &amp;times; (mean velocity gradient). The destruction rate on the other hand, is equal to &amp;epsilon;/T, where T is the turbulent time scale which is proportional to k/&amp;epsilon; and &amp;epsilon; is the rate at which the turbulent energy is dissipated by viscosity.</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>A feature of the k-&amp;epsilon; model is that this model predicts too large turbulent energy levels in the areas with large rates of strain <del style="font-weight: bold; text-decoration: none;">– </del>which is typically in stagnation point flows. Therefore, the problem is not the stagnation point per se, but the large strain rates which prevail under these conditions. In the literature many proposals can be found to overcome these problems.</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>A feature of the k-&amp;epsilon; model is that this model predicts too large turbulent energy levels in the areas with large rates of strain <ins style="font-weight: bold; text-decoration: none;">&amp;mdash; </ins>which is typically in stagnation point flows. Therefore, the problem is not the stagnation point per se, but the large strain rates which prevail under these conditions. In the literature many proposals can be found to overcome these problems.</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>One possibility to solve the stagnation point anomaly is to modify the production term in the kinetic energy equation (e.g. Kato and Launder (1993), Menter (1992), Menter ''et al.'' (1997), Strahle (1985)). Menter ''et al.'' (1997) showed that in a boundary layer type flow with the dominant strain rate S = &amp;part;U/&amp;part;x the production term is:</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>One possibility to solve the stagnation point anomaly is to modify the production term in the kinetic energy equation (e.g. Kato and Launder (1993), Menter (1992), Menter ''et al.'' (1997), Strahle (1985)). Menter ''et al.'' (1997) showed that in a boundary layer type flow with the dominant strain rate S = &amp;part;U/&amp;part;x the production term is:</div></td></tr> </table> Dave.Ellacott https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-12_Description&diff=11139&oldid=prev Niek.verhoeven at 17:15, 29 August 2009 2009-08-29T17:15:41Z <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 17:15, 29 August 2009</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l148">Line 148:</td> <td colspan="2" class="diff-lineno">Line 148:</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 3-12|description=UFR 3-12 Description|references=UFR 3-12 References|testcase=UFR 3-12 Test Case|evaluation=UFR 3-12 Evaluation|qualityreview=UFR 3-12 Quality Review|bestpractice=UFR 3-12 Best Practice Advice|relatedACs=UFR 3-12 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 3-12|description=UFR 3-12 Description|references=UFR 3-12 References|testcase=UFR 3-12 Test Case|evaluation=UFR 3-12 Evaluation|qualityreview=UFR 3-12 Quality Review|bestpractice=UFR 3-12 Best Practice Advice|relatedACs=UFR 3-12 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_3-12_Description&diff=8424&oldid=prev Daveg: UFR 3-12 Description moved to Silver:UFR 3-12 Description 2009-04-07T12:21:00Z <p><a href="/w/index.php/UFR_3-12_Description" title="UFR 3-12 Description">UFR 3-12 Description</a> moved to <a href="/w/index.php/Silver:UFR_3-12_Description" class="mw-redirect" title="Silver:UFR 3-12 Description">Silver:UFR 3-12 Description</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 12:21, 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_3-12_Description&diff=5107&oldid=prev David.Fowler: /* Turbulent Kinetic Energy Modifications */ 2009-03-11T17:05:59Z <p><span dir="auto"><span class="autocomment">Turbulent Kinetic Energy Modifications</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 17:05, 11 March 2009</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l110">Line 110:</td> <td colspan="2" class="diff-lineno">Line 110:</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;center&gt;&lt;sub&gt;[[Image:U3-12d32_files_image006.gif]] &lt;/sub&gt;&lt;/center&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>&lt;center&gt;&lt;sub&gt;[[Image:U3-12d32_files_image006.gif]] &lt;/sub&gt;&lt;/center&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" 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 exact formulation of the dominant strain rate is linear and can even change sign. However in the two-equation model is this not the case. The quadratic term increases much stronger, regardless if the flow is accelerated, or in the UFR considered here, decelerated. This quadratic term can be replaced by |S|&amp;middot;|&amp;Omega;|, where |S| is the strain rate as defined above and |&amp;Omega;|is the vorticity tensor. With this formulation the production term vanishes in irrotational flows and hence overcomes the problematic of the stagnation point flow. However, physically it is not correct that the production term P&lt;sub&gt;k&lt;/sub&gt; is equal to zero in irrotational flows.</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 exact formulation of the dominant strain rate is linear and can even change sign. However in the two-equation model is this not the case. The quadratic term increases much stronger, regardless if the flow is accelerated, or in the UFR considered here, decelerated. This quadratic term can be replaced by |S|&amp;middot;|&amp;Omega;|, where |S| is the strain rate as defined above and |&amp;Omega;| is the vorticity tensor. With this formulation the production term vanishes in irrotational flows and hence overcomes the problematic of the stagnation point flow. However, physically it is not correct that the production term P&lt;sub&gt;k&lt;/sub&gt; is equal to zero in irrotational flows.</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>In a similar way Kato and Launder (1993) modified P&lt;sub&gt;k&lt;/sub&gt; while Menter (1992) substituted the strain rate with the vorticity in the production term in the following way:</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>In a similar way Kato and Launder (1993) modified P&lt;sub&gt;k&lt;/sub&gt; while Menter (1992) substituted the strain rate with the vorticity in the production term in the following way:</div></td></tr> </table> David.Fowler https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-12_Description&diff=5106&oldid=prev David.Fowler at 17:05, 11 March 2009 2009-03-11T17:05:15Z <p></p> <a href="//kbwiki.ercoftac.org/w/index.php?title=UFR_3-12_Description&amp;diff=5106&amp;oldid=5105">Show changes</a> David.Fowler https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-12_Description&diff=5105&oldid=prev David.Fowler: /* Preface */ 2009-03-11T16:55:01Z <p><span dir="auto"><span class="autocomment">Preface</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 16:55, 11 March 2009</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l17">Line 17:</td> <td colspan="2" class="diff-lineno">Line 17:</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>== Preface ==</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>== Preface ==</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 underlying flow regime (UFR) considered is the flow in a stagnation point. This type of flow regime is of considerable technical relevance since it occurs whenever a flow impinges onto a solid object, typically in turbo-machinery or the leading edge of an aerofoil. Nowadays, for the determination of the flow-field in these configurations, CFD is used and hence this URF is always a part of such calculations. However, since the flow in this region is usually turbulent the predictions depend strongly on the quality of the chosen turbulence model. It is well known that the flow in stagnation point is often incorrectly predicted by the turbulence models. Even when the stagnation point region is not of interest per se[[UFR 3-12 References#ftn1|[1] ]], any erroneous calculation can distort the rest of the computed flow field, for example in the case for the prediction of heat transfer in the vicinity of the stagnation point. An overproduction of turbulent kinetic energy, as is typically predicted by two-equation turbulence models, results in an overestimation of heat transfer. It is evident that this failure is of strong relevance for the design of cooled turbine blades.</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 underlying flow regime (UFR) considered is the flow in a stagnation point. This type of flow regime is of considerable technical relevance since it occurs whenever a flow impinges onto a solid object, typically in turbo-machinery or the leading edge of an aerofoil. Nowadays, for the determination of the flow-field in these configurations, CFD is used and hence this URF is always a part of such calculations. However, since the flow in this region is usually turbulent the predictions depend strongly on the quality of the chosen turbulence model. It is well known that the flow in stagnation point is often incorrectly predicted by the turbulence models. Even when the stagnation point region is not of interest per se[[UFR 3-12 References#ftn1|[1]]], any erroneous calculation can distort the rest of the computed flow field, for example in the case for the prediction of heat transfer in the vicinity of the stagnation point. An overproduction of turbulent kinetic energy, as is typically predicted by two-equation turbulence models, results in an overestimation of heat transfer. It is evident that this failure is of strong relevance for the design of cooled turbine blades.</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>The choice of the turbulence model is always a compromise between accuracy of the predicted results and the numerics (i.e. stability, convergence, CPU time). In the following the focus is on the two-equation models. This type of turbulence model is widely used because of its numerical stability and relatively simple formulation. The main disadvantage of the two-equation models is their poor performance under adverse pressure gradients, which is also an important feature of stagnation point flows. In order to overcome these deficits of the model many different modifications where proposed.</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>The choice of the turbulence model is always a compromise between accuracy of the predicted results and the numerics (i.e. stability, convergence, CPU time). In the following the focus is on the two-equation models. This type of turbulence model is widely used because of its numerical stability and relatively simple formulation. The main disadvantage of the two-equation models is their poor performance under adverse pressure gradients, which is also an important feature of stagnation point flows. In order to overcome these deficits of the model many different modifications where proposed.</div></td></tr> </table> David.Fowler https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-12_Description&diff=5104&oldid=prev David.Fowler: /* Preface */ 2009-03-11T16:54:43Z <p><span dir="auto"><span class="autocomment">Preface</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 16:54, 11 March 2009</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l17">Line 17:</td> <td colspan="2" class="diff-lineno">Line 17:</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>== Preface ==</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>== Preface ==</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 underlying flow regime (UFR) considered is the flow in a stagnation point. This type of flow regime is of considerable technical relevance since it occurs whenever a flow impinges onto a solid object, typically in turbo-machinery or the leading edge of an aerofoil. Nowadays, for the determination of the flow-field in these configurations, CFD is used and hence this URF is always a part of such calculations. However, since the flow in this region is usually turbulent the predictions depend strongly on the quality of the chosen turbulence model. It is well known that the flow in stagnation point is often incorrectly predicted by the turbulence models. Even when the stagnation point region is not of interest per se [[UFR 3-12 References#ftn1|[1] ]], any erroneous calculation can distort the rest of the computed flow field, for example in the case for the prediction of heat transfer in the vicinity of the stagnation point. An overproduction of turbulent kinetic energy, as is typically predicted by two-equation turbulence models, results in an overestimation of heat transfer. It is evident that this failure is of strong relevance for the design of cooled turbine blades.</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 underlying flow regime (UFR) considered is the flow in a stagnation point. This type of flow regime is of considerable technical relevance since it occurs whenever a flow impinges onto a solid object, typically in turbo-machinery or the leading edge of an aerofoil. Nowadays, for the determination of the flow-field in these configurations, CFD is used and hence this URF is always a part of such calculations. However, since the flow in this region is usually turbulent the predictions depend strongly on the quality of the chosen turbulence model. It is well known that the flow in stagnation point is often incorrectly predicted by the turbulence models. Even when the stagnation point region is not of interest per se[[UFR 3-12 References#ftn1|[1] ]], any erroneous calculation can distort the rest of the computed flow field, for example in the case for the prediction of heat transfer in the vicinity of the stagnation point. An overproduction of turbulent kinetic energy, as is typically predicted by two-equation turbulence models, results in an overestimation of heat transfer. It is evident that this failure is of strong relevance for the design of cooled turbine blades.</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>The choice of the turbulence model is always a compromise between accuracy of the predicted results and the numerics (i.e. stability, convergence, CPU time). In the following the focus is on the two-equation models. This type of turbulence model is widely used because of its numerical stability and relatively simple formulation. The main disadvantage of the two-equation models is their poor performance under adverse pressure gradients, which is also an important feature of stagnation point flows. In order to overcome these deficits of the model many different modifications where proposed.</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>The choice of the turbulence model is always a compromise between accuracy of the predicted results and the numerics (i.e. stability, convergence, CPU time). In the following the focus is on the two-equation models. This type of turbulence model is widely used because of its numerical stability and relatively simple formulation. The main disadvantage of the two-equation models is their poor performance under adverse pressure gradients, which is also an important feature of stagnation point flows. In order to overcome these deficits of the model many different modifications where proposed.</div></td></tr> </table> David.Fowler https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-12_Description&diff=5103&oldid=prev David.Fowler: /* Preface */ 2009-03-11T16:54:29Z <p><span dir="auto"><span class="autocomment">Preface</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 16:54, 11 March 2009</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l17">Line 17:</td> <td colspan="2" class="diff-lineno">Line 17:</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>== Preface ==</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>== Preface ==</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 underlying flow regime (UFR) considered is the flow in a stagnation point. This type of flow regime is of considerable technical relevance since it occurs whenever a flow impinges onto a solid object, typically in turbo-machinery or the leading edge of an aerofoil. Nowadays, for the determination of the flow-field in these configurations, CFD is used and hence this URF is always a part of such calculations. However, since the flow in this region is usually turbulent the predictions depend strongly on the quality of the chosen turbulence model. It is well known that the flow in stagnation point is often incorrectly predicted by the turbulence models. Even when the stagnation point region is not of interest per se[UFR 3-12 References#ftn1|[1] ]], any erroneous calculation can distort the rest of the computed flow field, for example in the case for the prediction of heat transfer in the vicinity of the stagnation point. An overproduction of turbulent kinetic energy, as is typically predicted by two-equation turbulence models, results in an overestimation of heat transfer. It is evident that this failure is of strong relevance for the design of cooled turbine blades.</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 underlying flow regime (UFR) considered is the flow in a stagnation point. This type of flow regime is of considerable technical relevance since it occurs whenever a flow impinges onto a solid object, typically in turbo-machinery or the leading edge of an aerofoil. Nowadays, for the determination of the flow-field in these configurations, CFD is used and hence this URF is always a part of such calculations. However, since the flow in this region is usually turbulent the predictions depend strongly on the quality of the chosen turbulence model. It is well known that the flow in stagnation point is often incorrectly predicted by the turbulence models. Even when the stagnation point region is not of interest per se <ins style="font-weight: bold; text-decoration: none;">[</ins>[UFR 3-12 References#ftn1|[1] ]], any erroneous calculation can distort the rest of the computed flow field, for example in the case for the prediction of heat transfer in the vicinity of the stagnation point. An overproduction of turbulent kinetic energy, as is typically predicted by two-equation turbulence models, results in an overestimation of heat transfer. It is evident that this failure is of strong relevance for the design of cooled turbine blades.</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>The choice of the turbulence model is always a compromise between accuracy of the predicted results and the numerics (i.e. stability, convergence, CPU time). In the following the focus is on the two-equation models. This type of turbulence model is widely used because of its numerical stability and relatively simple formulation. The main disadvantage of the two-equation models is their poor performance under adverse pressure gradients, which is also an important feature of stagnation point flows. In order to overcome these deficits of the model many different modifications where proposed.</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>The choice of the turbulence model is always a compromise between accuracy of the predicted results and the numerics (i.e. stability, convergence, CPU time). In the following the focus is on the two-equation models. This type of turbulence model is widely used because of its numerical stability and relatively simple formulation. The main disadvantage of the two-equation models is their poor performance under adverse pressure gradients, which is also an important feature of stagnation point flows. In order to overcome these deficits of the model many different modifications where proposed.</div></td></tr> </table> David.Fowler https://kbwiki.ercoftac.org/w/index.php?title=UFR_3-12_Description&diff=5102&oldid=prev David.Fowler: /* Preface */ 2009-03-11T16:54:15Z <p><span dir="auto"><span class="autocomment">Preface</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 16:54, 11 March 2009</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l17">Line 17:</td> <td colspan="2" class="diff-lineno">Line 17:</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>== Preface ==</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>== Preface ==</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 underlying flow regime (UFR) considered is the flow in a stagnation point. This type of flow regime is of considerable technical relevance since it occurs whenever a flow impinges onto a solid object, typically in turbo-machinery or the leading edge of an aerofoil. Nowadays, for the determination of the flow-field in these configurations, CFD is used and hence this URF is always a part of such calculations. However, since the flow in this region is usually turbulent the predictions depend strongly on the quality of the chosen turbulence model. It is well known that the flow in stagnation point is often incorrectly predicted by the turbulence models. Even when the stagnation point region is not of interest per se[#<del style="font-weight: bold; text-decoration: none;">_ftn1 </del>[1]], any erroneous calculation can distort the rest of the computed flow field, for example in the case for the prediction of heat transfer in the vicinity of the stagnation point. An overproduction of turbulent kinetic energy, as is typically predicted by two-equation turbulence models, results in an overestimation of heat transfer. It is evident that this failure is of strong relevance for the design of cooled turbine blades.</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 underlying flow regime (UFR) considered is the flow in a stagnation point. This type of flow regime is of considerable technical relevance since it occurs whenever a flow impinges onto a solid object, typically in turbo-machinery or the leading edge of an aerofoil. Nowadays, for the determination of the flow-field in these configurations, CFD is used and hence this URF is always a part of such calculations. However, since the flow in this region is usually turbulent the predictions depend strongly on the quality of the chosen turbulence model. It is well known that the flow in stagnation point is often incorrectly predicted by the turbulence models. Even when the stagnation point region is not of interest per se[<ins style="font-weight: bold; text-decoration: none;">UFR 3-12 References</ins>#<ins style="font-weight: bold; text-decoration: none;">ftn1|</ins>[1<ins style="font-weight: bold; text-decoration: none;">] </ins>]], any erroneous calculation can distort the rest of the computed flow field, for example in the case for the prediction of heat transfer in the vicinity of the stagnation point. An overproduction of turbulent kinetic energy, as is typically predicted by two-equation turbulence models, results in an overestimation of heat transfer. It is evident that this failure is of strong relevance for the design of cooled turbine blades.</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>The choice of the turbulence model is always a compromise between accuracy of the predicted results and the numerics (i.e. stability, convergence, CPU time). In the following the focus is on the two-equation models. This type of turbulence model is widely used because of its numerical stability and relatively simple formulation. The main disadvantage of the two-equation models is their poor performance under adverse pressure gradients, which is also an important feature of stagnation point flows. In order to overcome these deficits of the model many different modifications where proposed.</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>The choice of the turbulence model is always a compromise between accuracy of the predicted results and the numerics (i.e. stability, convergence, CPU time). In the following the focus is on the two-equation models. This type of turbulence model is widely used because of its numerical stability and relatively simple formulation. The main disadvantage of the two-equation models is their poor performance under adverse pressure gradients, which is also an important feature of stagnation point flows. In order to overcome these deficits of the model many different modifications where proposed.</div></td></tr> </table> David.Fowler