TY - GEN
T1 - Hypersonic boundary-layer transition
T2 - 48th AIAA Fluid Dynamics Conference, 2018
AU - Meersman, John A.
AU - Hader, Christoph
AU - Fasel, Hermann F.
N1 - Funding Information:
This work was supported by AFOSR Grant FA9550-15-1-0265, with Dr. Ivett Leyva serving as the program manager. Computer time was provided by the US Army Engineering Research and Development Center (ERDC) under the Department of Defense (DOD) High Performance Computing Modernization Program (HPCMP) AFOSR26292. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the Air Force Office of Scientific Research or the U. S. Government.
Publisher Copyright:
© 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.
PY - 2018
Y1 - 2018
N2 - A side-by-side comparison of high-order accurate Direct Numerical Simulations (DNS) conducted for a straight and flared cone at Mach 6 is presented in order to investigate the effects of geometry on the linear and nonlinear stages of laminar-turbulent transition. The cone geometries and the flow conditions of the simulations are chosen to closely match those of the experiments conducted at the Boeing/AFOSR Mach 6 Quiet Tunnel (BAM6QT) at Purdue University. Linear stability regime calculations using low amplitude short-duration pulse simulations indicate, as expected, that the cone flare shifts the dominant second mode frequencies to higher values and significantly increases the spatial growth rates. Secondary instability investigations revealed that for both geometries the fundamental resonance would be most likely the relevant mechanism leading to transition for the Purdue quiet tunnel conditions. However, the azimuthal wave number leading to the strongest resonance (largest N-factor for secondary instability) has shifted to lower values for the flared cone compared with the straight cone. For both cases, so-called “controlled” breakdown simulations presented in this paper showed a similar pattern of “hot streaks” that appear, disappear, and reappear further downstream which was also observed in the Purdue experiments (for the flared cone only) using temperature sensitive paint (TSP). A detailed flow field analysis of the DNS data confirmed that these streaks are generated by a streamwise vortical mode. Both geometries showed good agreement of the streamwise development of the secondary streak pattern and subsequent breakdown to smaller structures in the final breakdown. The results presented in this paper confirm the destabilizing effect of the cone flare with regard to the primary instability. In addition, the flared cone is also more unstable with respect to the secondary instability, leading to larger growth rates of the secondary disturbance wave after resonance onset. As a result, the cone flare accelerates the transition process leading to the breakdown to turbulence further upstream compared to the straight cone. Hoewever, the qualitative similarities of the nonlinear behavior between the flared and straight cone suggest that for the BAM6QT quiet conditions the fundamental resonance is likely the relevant nonlinear breakdown mechanism for the straight cone as well.
AB - A side-by-side comparison of high-order accurate Direct Numerical Simulations (DNS) conducted for a straight and flared cone at Mach 6 is presented in order to investigate the effects of geometry on the linear and nonlinear stages of laminar-turbulent transition. The cone geometries and the flow conditions of the simulations are chosen to closely match those of the experiments conducted at the Boeing/AFOSR Mach 6 Quiet Tunnel (BAM6QT) at Purdue University. Linear stability regime calculations using low amplitude short-duration pulse simulations indicate, as expected, that the cone flare shifts the dominant second mode frequencies to higher values and significantly increases the spatial growth rates. Secondary instability investigations revealed that for both geometries the fundamental resonance would be most likely the relevant mechanism leading to transition for the Purdue quiet tunnel conditions. However, the azimuthal wave number leading to the strongest resonance (largest N-factor for secondary instability) has shifted to lower values for the flared cone compared with the straight cone. For both cases, so-called “controlled” breakdown simulations presented in this paper showed a similar pattern of “hot streaks” that appear, disappear, and reappear further downstream which was also observed in the Purdue experiments (for the flared cone only) using temperature sensitive paint (TSP). A detailed flow field analysis of the DNS data confirmed that these streaks are generated by a streamwise vortical mode. Both geometries showed good agreement of the streamwise development of the secondary streak pattern and subsequent breakdown to smaller structures in the final breakdown. The results presented in this paper confirm the destabilizing effect of the cone flare with regard to the primary instability. In addition, the flared cone is also more unstable with respect to the secondary instability, leading to larger growth rates of the secondary disturbance wave after resonance onset. As a result, the cone flare accelerates the transition process leading to the breakdown to turbulence further upstream compared to the straight cone. Hoewever, the qualitative similarities of the nonlinear behavior between the flared and straight cone suggest that for the BAM6QT quiet conditions the fundamental resonance is likely the relevant nonlinear breakdown mechanism for the straight cone as well.
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U2 - 10.2514/6.2018-3851
DO - 10.2514/6.2018-3851
M3 - Conference contribution
AN - SCOPUS:85051289107
SN - 9781624105531
T3 - 2018 Fluid Dynamics Conference
BT - 2018 Fluid Dynamics Conference
PB - American Institute of Aeronautics and Astronautics Inc, AIAA
Y2 - 25 June 2018 through 29 June 2018
ER -