 | Costantini M. Experimental analysis of geometric, pressure gradient and surface temperature effects on boundary-layer transition in compressible high Reynolds number flows: Diss. ... Dr.-Ing. / Deutsches Zentrum für Luft- und Raumfahrt, Institut für Aerodynamik und Strömungstechnik, Göttingen. - Köln: DLR, 2016. - v, 286 p.: ill. - (Forschungsbericht; 2016-62). - Res. also Germ. - Bibliogr.: p.261-279. - ISSN 1434-8454
Шифр: (Pr 1120/2016-62) 02
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1 Introduction ............................................... 1
1.1 Scope of work .............................................. 5
1.2 Outline ................................................... 10
2 Theoretical considerations and available knowledge from
previous work ............................................. 11
2.1 An introduction to boundary-layer transition .............. 11
2.2 The road to turbulence in two-dimensional boundary
layers .................................................... 13
2.2.1 Linear amplification of the disturbances (linear
stability theory) .................................. 14
2.2.2 Boundary-layer receptivity to external
disturbances ....................................... 17
2.2.3 Non-linear amplification of the disturbances and
breakdown to turbulence ............................ 19
2.2.4 Transition region and measurement of boundary-
layer transition ................................... 19
2.3 Boundary-layer stability modifiers ........................ 21
2.3.1 Streamwise pressure gradient ....................... 23
2.3.2 Surface mass transfer .............................. 24
2.3.3 Surface heat transfer .............................. 24
2.3.4 Combination of streamwise pressure gradient and
surface heat transfer .............................. 25
2.4 Transition prediction based on linear, local stability
theory (eN method) ........................................ 26
2.5 Past work on the effect of surface imperfections on
boundary-layer stability and transition with emphasis on
forward-facing steps ...................................... 29
3 Experimental setup ........................................ 37
3.1 Cryogenic Ludwieg-Tube Göttingen (DNW-KRG) ................ 37
3.2 Design of the model cross-section ......................... 40
3.2.1 Numerical tools .................................... 41
3.2.2 Wind-tunnel model requirements and model cross-
section shape ...................................... 42
3.3 Wind-tunnel model ......................................... 46
3.4 Instramentation of the wind-tunnel model .................. 50
3.4.1 Temperature-sensitive paint (TSP) measurement
technique .......................................... 51
3.4.2 Pressure taps and thermocouples .................... 52
4 Data analysis ............................................. 55
4.1 TSP data acquisition ...................................... 55
4.2 Detection of boundary-layer transition .................... 56
4.3 Definition and evaluation of the test parameters .......... 59
5 Results ................................................... 63
5.1 Smooth configuration ...................................... 64
5.1.1 Effect of the Mach number .......................... 65
5.1.2 Effect of pressure gradient and wall temperature
ratio and comparison with published work ........... 70
5.1.3 Summary of investigations with the smooth
configuration ...................................... 80
5.2 Step configurations ....................................... 81
5.2.1 Effect of the step height .......................... 82
5.2.2 Effect of the chord Reynolds number ................ 85
5.2.3 Effect of the streamwise pressure gradient ......... 88
5.2.4 Effect of the wall temperature ratio ............... 90
5.2.5 Effect of the Mach number .......................... 94
6 Discussion of the results ................................. 98
6.1 Combined effect of forward-facing steps and chord
Reynolds number ........................................... 98
6.2 Combined effect of forward-facing steps and streamwise
pressure gradient ........................................ 101
6.2.1 Sensitivity of boundary-layer transition to the
effect of forward-facing steps at different
pressure gradients ................................ 101
6.2.2 Summary and discussion of the results obtained
at M = 0.77 and standard wall temperature ratio ... 106
6.3 Combined effect of forward-facing steps, pressure
gradient, and Mach number ................................ 112
6.4 Summary and discussion of the results at standard TJTaw
and comparison with data from previous work .............. 116
6.4.1 Comparison with results from previous work ........ 120
6.4.2 Increase in amplification factors (АЛО due to
forward-facing steps .............................. 127
6.5 Combined effect of forward-facing steps and wall
temperature ratio ........................................ 129
6.5.1 Step-1 configuration (h/Shh < 0.5) ................ 130
6.5.2 Step-2 and step-3 configurations (0.5 < h/öhh <
1.5) .............................................. 133
6.5.3 Analysis and discussion of the results ............ 135
6.5.4 Effect of forward-facing steps on boundary-layer
transition at the same, reduced wall temperature
ratio ............................................. 145
6.5.5 Summary of the results obtained at different
wall temperature ratios in the presence of
forward-facing steps .............................. 147
7 Conclusion ............................................... 149
7.1 Summary .................................................. 149
7.2 Outlook .................................................. 153
Appendix ...................................................... 159
A Supplements to the introduction .......................... 159
A.l Historical review of the effects of surface
imperfections in past laminar flow research .............. 159
A.2 Flight envelope for hypothetical transport aircraft
employing natural laminar flow wings ..................... 161
В Experimental setup ....................................... 163
B.l Results of boundary-layer computations and linear
stability analysis of the model cross-section ............ 163
B.2 Challenges for the application at DNW-KRG of typical
solutions for low-speed transition experiments on flat
plates ................................................... 165
B.3 Model surface quality .................................... 167
B.3.1 Analysis of the surface quality at the step
location .......................................... 167
B.3.2 Analysis (and improvement) of model surface
quality ........................................... 170
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