DESIGN OF A CONE-CYLINDER-FLARE CONFIGURATION FOR HYPERSONIC BOUNDARY-LAYER STABILITY ANALYSES AND MEASUREMENTS WITH ATTACHED AND SEPARATED FLOWS
Esquieu1, S. P. Schneider2, E. K. Benitez3, J-P Brazier4
1CEA, The French Alternative Energies and Atomic Energy Commission, Le Barp, France
2School of Aeronautics and Astronautics, Purdue University, West Lafayette, Indiana, USA
3US Air Force Research Laboratory, Wright-Patterson Air Force Base, OH, 45433
4ONERA/DMPE, Université de Toulouse, F-31055 Toulouse, France
Corresponding author: email@example.com
The stability of hypersonic boundary-layer over two axisymmetric cone-cylinder-flare configurations at Mach 6 and zero-degree angle of attack is investigated for different Reynolds numbers.
Shapes have been designed for wind tunnel test experiments (see figure 1) following specific aerodynamic goals. The first configuration (CCF3-5) has been designed in order to keep an attached boundary-layer all along the object and to investigate the effects of pressure gradients, flow expansion and recompression on the hypersonic boundary-layer stability . The second geometry (CCF10) is an evolution of the initial shape with an increased flare angle in order to generate a significant flow separation. The goal here is to investigate the development of boundary layer instabilities in the case of a separated hypersonic flow.
A detailed description of the two cone-cylinder-flare configurations as well as a thorough study of the aerodynamic flows obtained in fully laminar conditions (see figure 2) will be presented.
For the first configuration with attached boundary layer, linear stability theory (LST) and linear parabolized stability equations (PSE) are used to predict the amplification rates of the boundary-layer disturbances, i.e the dominant Mack’s second mode waves in this case. The stability analyses are performed with the 2D-axisymmetric version of the STABL software suite from the University of Minnesota in LST and PSE modes. Code comparisons with the ONERA Mamout solver are also realized in LST mode. The numerical stability results are compared to wind tunnel measurements obtained in the BAM6QT (Boeing AFOSR Mach-6 Quiet Tunnel) wind tunnel of Purdue University. The semiempirical eN method allows to correlate transition with the integrated growth of the linear instability waves (see figure 3). Finally, the computed N factors which correspond roughly to wave amplitude are compared to measured power spectra.
The second geometry with the separation bubble was also tested in the BAM6QT wind tunnel. Second mode fluctuations as well as a different type of travelling wave were observed in PCB, Kulite, and FLDI measurements  (see figure 4). The travelling waves are not predicted by linear stability computations and are believed to be generated by the shear layer above the separation bubble.
Recent studies are devoted to the analyses of boundary-layer instabilities in the presence of a flow separation [3,4,5], some elements will be presented in this paper.
 Esquieu, S., Benitez, E., Schneider, S., and Brazier, J.-P., “Flow and Stability Analysis of a Hypersonic Boundary-Layer Over an Axisymmetric Cone-Cylinder-Flare Configuration,” AIAA Paper 2019-2115, 2019. https://doi.org/10.2514/6.2019–2115
 Lugrin, M., Nicolas, F., Severac, N., Tobeli,, J-P, Beneddine, S., Garnier, E., Esquieu, S. & Bur, R.. (2022). Transitional shockwave/boundary layer interaction experiments in the R2Ch blowdown wind tunnel. Experiments in Fluids. https://doi.org/63. 10.1007/s00348-022-03395-9
 Li, F. & Choudhari, M. & Paredes, P. & Scholten, A. (2022). Nonlinear Evolution of Instabilities in a Laminar Separation Bubble at Hypersonic Mach Number. https://doi.org/10.2514/6.2022-3855