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Synchronization of second-mode instability waves for high-enthalpy hypersonic boundary layers

Published online by Cambridge University Press:  25 January 2018

Leonardo C. Salemi Open the ORCID record for Leonardo C. Salemi [Opens in a new window]  and
Hermann F. Fasel
Leonardo C. Salemi
Affiliation:
Department of Aerospace and Mechanical Engineering, The University of Arizona, Tucson AZ 85721, USA
Hermann F. Fasel*
Affiliation:
Department of Aerospace and Mechanical Engineering, The University of Arizona, Tucson AZ 85721, USA
*
†Email address for correspondence: faselh@email.arizona.edu
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Abstract

The stability of a hypersonic boundary layer for a $5^{\circ }$ 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.

JFM classification

Boundary Layers: Boundary layer stability Compressible Flows: Compressible boundary layers Aerodynamics: High-speed flow
Type
JFM Rapids
Information
Journal of Fluid Mechanics , Volume 838 , 10 March 2018 , R2
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Copyright
© 2018 Cambridge University Press 

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