Laminar-turbulent boundary layer transition

Underlying Flow Regime 3-04 © copyright ERCOFTAC 2004

Quality Review

In order to accept this UFR the following modifications and additional information should be added:

1. Transitional data should be included, indicating the laminar instability, turbulent spot appearance and the length of the transitional region.

2. Inconsistencies in measurements should be eliminated. Those include positive friction coefficient values in areas where separation is claimed, relatively small shape factor values in areas where a laminar separation is reported.

3. Additional proof of the two-dimensionality of the flow should be provided (visualizations, momentum and energy balance).

4. Analysis of the measured velocity profiles should be performed in order to reconstitute the nature of the boundary layer. Once the whole experiment is set soundly on a coherent basis, comparisons with the computational results can be carried out and a sound evaluation of transition computational accuracy can be performed.

5. The review of transition should be more complete. It is suggested to start with the paper of Mayle (1991) as a basis, where the laminar separation bubble is included, a transition mode, which is essential for this UFR. On the other hand, existing references do not provide the issues (computational and experimental) that have appeared through the years offering different theoretical approaches to a problem with no definitive and coherent formulation yet.

6. Explanation among experimental and theoretical calculations should be looked upon with care. For instance, assessment that we deal with a case of by-pass transition, when external turbulence is 1% without any other indications cannot withstand criticism.

7. Finally a list of corrections is provided at the end.

Underlying Flow Regime Title: LaminarTurbulent Boundary Layer Transition

UFR Author and UFR number: Institute of Thermal Machinery
Technical University of Czestochowa
UFR3-04

Reviewer (Name/Organization): K.D. Papailiou
Laboratory of Thermal Turbomachinery
National Technical University of Athens

1	TOP LEVEL CHECK	YES	NO	CO
1. 1	Is the selected test-case study a good representation of the assigned UFR?	þ
1. 2	Does the test-case study include both flow measurements and CFD calculations?	þ
1. 3	Does the document under review comply with the D32 template	þ
1. 4	Should any parts be expanded, condensed or deleted?	þ		þ
1. 5	Are the illustrations and their captions clear and informative?	þ
1. 6	Are the references adequate and complete?	þ
1. 7	If any hyperlinks are used, do these function correctly?	þ
Comments:

Section 4 should be expanded to account for inconsistencies in the measurements.

Section 6 more in agreement with general comments

DETAILED CHECK

2	REVIEW OF UFR STUDIES AND CHOICE OF TEST CASE	YES	NO	CO
2. 1	Have past studies of the UFR been reviewed adequately?		þ	þ
2. 2	Is the chosen test-case study selected from an established database or comparison exercise?	þ
2. 3	Have the test-case experiments been devised for CFD validation?	þ		þ
Comments:
2.1: Past studies for this particular UFR do not exist. However, very similar measurements have appeared, as for instance the VKI turbine cascade. Some comments/comparisons should appear in the documentation, particular in relation to what this experiment offers compared to the previous ones.
2.3: See 2.1

3	DESCRIPTION OF THE STUDY TEST CASE	YES	NO	CO
3. 1	Is the geometry described adequately, including an appropriate sketch?	þ
3. 2	Are the flow parameters defining the flow regime specified?	þ
3. 3	Are the principal measured quantities (i.e. those by which success or failure of CFD is to be judged) specified?	þ
3. 4	Is the description fully self-contained and sufficiently detailed? (The level of detail required depends on whether a hyperlink to a detailed database is provided)	þ		þ
Comments:
3.3: The description of the facility, the experimental set up and the measuring techniques is not detailed. More details are welcome. More quantities related to the transition region should appear.

4	Test CASE EXPERIMENTS	YES	NO	CO
4. 1	Is the test-case facility described adequately?	þ		þ
4. 2	Are the measurement techniques explained?	þ		þ
4. 3	Is the quality/accuracy of the measured data discussed?	þ		þ
4. 4	Are the following quality aspects addressed in this discussion:
a)	Closeness of flow to target/design conditions?		þ
b)	Accuracy estimation of measured quantities?	þ
c)	Checks on global conservation of conserved quantities?		þ	þ
d)	Consistency in the measurements of different quantities?		þ	þ
e)	Other (briefly describe)
4. 5	Is the evidence of data quality judged to be sufficient?		þ
4. 6	Is the information provided at the flow boundaries sufficient to specify or estimate reasonably well the boundary conditions required for a CFD calculation?		þ
4. 7	Is the overall discussion self-contained and sufficiently detailed? (the level of detail required depends on whether a hyperlink to a detailed database is provided)		þ
Comments:
4.1, 4.2 and 4.3: The answer is positive in the sense that the experiment can be reconstituted and utilized. A few comments on possible deficiencies are mentioned. The one on the two-dimensionality of the flow is not adequate though. Measurements for adequately describing the transition region are lacking.
4.4c and 4.4d: no energy and momentum balance is applied to measurements.

5	CFD METHODS	YES	NO	CO
5. 1	Is an overview given of the methods used?	þ
5. 2	Have the following aspects of the methods used been explained adequately:-
a)	The codes employed?	þ
b)	The turbulence/physical models used?	þ
c)	The wall treatments applied?	þ
d)	The numerical boundary conditions?	þ
5. 3	Are comments made on how well the boundary conditions replicate conditions in the test rig?		þ	þ
5. 4	Is the quality of the calculations discussed?		þ	þ
5. 5	Are the following quality aspects addressed in this discussion?
a)	The discretisation scheme(s) and solver(s)?	þ
b)	The sufficiency of grid resolution(s)?	þ
c)	Sensitivities to uncertainties in the boundary conditions		þ
d)	Comparisons between separate calculations using the same physical model		þ
e)	Other (briefly describe)
5. 6	Is the evidence of CFD quality judged to be sufficient in all cases?	þ		þ
Comments:
5.3: It is left to the reader to decide. The boundary conditions used however are accurately described.
5.4: Not adequately and convincingly.
5.6: It is not possible to judge concerning the predictions because of uncertainties in the measurements.

6	COMPARISON OF CFD CALCULATIONS WITH EXPERIMENT	YES	NO	CO
6. 1	Are key comparisons of CFD results with experiment presented in the form of tables or plots?	þ
6. 2	Do these comparisons include the assessment quantities?	þ
6. 3	Are further comparisons available via hyperlinks to a results database?		þ
6. 4	Is the performance of the CFD calculations judged by comparison with experiments discussed and analyzed in all cases?	þ		þ
Comments:
6.4: It is not possible to judge concerning the predictions because of uncertainties in the measurements.

7	BEST PRACTICE ADVICE FOR THE UFR	YES	NO	CO
7. 1	Are model abilities for this test case discussed and analyzed in sufficient detail?		þ
7. 2	Are recommendations provided on which models should be used for this UFR?		þ
7. 3	Are these recommendations supported by the evidence?		þ
Comments:
Useful information is provided about work, which has been performed worldwide, but little advice is contained concerning the way that computations should be performed in order to obtain reliable and accurate results.

Errata

Page 13 after the formula: The pressures are not correctly defined.

Page 13, line 6 from bottom: No reference to laminar bubble in the experimental description.

Page 13 Figure 3: Computed inlet free-stream turbulence does not match the inlet experimental value.

Page 14, line 13 from the top: freestream instead of reestream.

Page 14, line 17 from the top: correct english.

Page 14, Figure 4: Visualization for separation and reattachment is missing. Separation is not present in the friction coefficient measured distributions. In the same figure transition is not clear and there is a discrepancy with Figure 7 (which is not in place). Transition at S_s=0.71 is not substantiated. Bypass type transition is not compatible with turbulence intensity of 1%. Measured velocity profiles at various positions should be analyzed to determine whether the boundary layer is laminar or turbulent.

Figure 7: Important differences appear between the two measurements of the skin friction. Why? Are they related to transition?

Page 15: It is not mentioned from the beginning that only steady state measurements will be considered.

Contributors: Andrzej Boguslawski - Technical University of Czestochowa