TY - JOUR
T1 - Synchronization of second-mode instability waves for high-enthalpy hypersonic boundary layers
AU - Salemi, Leonardo C.
AU - Fasel, Hermann F.
N1 - Funding Information:
Parts of this work were funded by the AFOSR/NASA National Center of Hypersonic Laminar-Turbulent Transition Research at the Texas A&M University under grant FA9550-08-1-0211, with Dr J. Schmisseur serving as program manager, and by the Air Force Office of Scientific Research (AFOSR) under grant FA9550-15-1-0265, with Dr I. Leyva serving as program manager. The authors thank Drs J. Jewell, J. Shepherd and H. Hornung for fruitful discussions.
Publisher Copyright:
© 2018 Cambridge University Press.
PY - 2018/3/10
Y1 - 2018/3/10
N2 - The stability of a hypersonic boundary layer for 5° half-angle cone at the Caltech T5 high-enthalpy flow conditions was investigated using direct numerical simulations. For the 'linear' stability investigations, the boundary layer was perturbed by small axisymmetric disturbances with very small amplitudes, and for the nonlinear regime, three-dimensional pulse disturbances with larger amplitudes were introduced. The surprising result from these investigations was that the 3D wave packet undergoes strong spatial modulations, which we have not observed for other experimental conditions (e.g. the Purdue BAM6QT). This modulation was found to be directly due to the synchronization between second-mode wave components and vorticity/entropy modes. Furthermore, it was found that a synchronization with slow acoustic waves leads to a sudden and strong emission of acoustic waves deep into the free stream, which was observed for both a linear wave train and a 3D nonlinear wave packet. Therefore, it can be concluded that this is a linear mechanism that is not suppressed by nonlinear effects.
AB - The stability of a hypersonic boundary layer for 5° half-angle cone at the Caltech T5 high-enthalpy flow conditions was investigated using direct numerical simulations. For the 'linear' stability investigations, the boundary layer was perturbed by small axisymmetric disturbances with very small amplitudes, and for the nonlinear regime, three-dimensional pulse disturbances with larger amplitudes were introduced. The surprising result from these investigations was that the 3D wave packet undergoes strong spatial modulations, which we have not observed for other experimental conditions (e.g. the Purdue BAM6QT). This modulation was found to be directly due to the synchronization between second-mode wave components and vorticity/entropy modes. Furthermore, it was found that a synchronization with slow acoustic waves leads to a sudden and strong emission of acoustic waves deep into the free stream, which was observed for both a linear wave train and a 3D nonlinear wave packet. Therefore, it can be concluded that this is a linear mechanism that is not suppressed by nonlinear effects.
KW - boundary layer stability
KW - compressible boundary layers
KW - high-speed flow
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U2 - 10.1017/jfm.2017.880
DO - 10.1017/jfm.2017.880
M3 - Article
AN - SCOPUS:85049784911
SN - 0022-1120
VL - 838
SP - R21-R214
JO - Journal of Fluid Mechanics
JF - Journal of Fluid Mechanics
ER -