Secondary instability of Mack mode disturbances in hypersonic boundary layers over micro-porous surface
File(s)
Accepted version
Author(s)
Xu, Jiakuan
Liu, Jianxin
Mughal, Mohammed S
Yu, Peixun
Bai, Junqiang
Type
Journal Article
Abstract
In laminar hypersonic boundary layers, it is known that secondary instability plays a crucial role in transition to turbulence. The secondary instability usually includes the fundamental mode, the subharmonic mode, and the detuned mode. Considerable research exists on the secondary instability mechanism in hypersonic boundary layers with the smooth wall condition. The topic of using micro-porous surfaces for disturbance stabilization has recently drawn interest. The stabilization and, thus, a possible delay in the transition arise due to a reduction in the growth rate of the primary Mack mode by the porous surface. This paper focuses on investigating whether the secondary instability mechanism of Mack modes can also be affected by a surface porosity condition. It is known that the primary Mack mode linear disturbances are changed significantly on the porous surface, and how it subsequently influences the secondary instability of the modified time varying basic flow is our concern. The analysis demonstrates that on the porous surface, as the amplitude of the primary Mack mode increases, the fundamental mode is not stable. Instead, the fundamental mode amplifies rapidly with increasing primary amplitudes. At larger secondary instability spanwise wavenumbers, when the primary amplitude exceeds a certain threshold value, the fundamental modes surpass the subharmonic modes and dominate the secondary instability. However, when the spanwise wavenumber is relatively small, especially at the spanwise wavenumber corresponding to the maximum growth rate of the subharmonic mode, the fundamental modes are weakened and lose their dominant position. We find that corresponding to different amplitudes of primary Mack mode disturbances affected by the porosity parameters, there are no strongly preferred interaction modes that dominate the secondary instability; this contrasts with smooth wall findings. We further find that the larger the pore size or porosity, the more severe the suppression of the fundamental mode.
Date Issued
2020-04-17
Date Acceptance
2020-03-19
Citation
Physics of Fluids, 2020, 32 (4)
ISSN
1070-6631
Publisher
AIP Publishing
Journal / Book Title
Physics of Fluids
Volume
32
Issue
4
Copyright Statement
© 2020 Owner. Published by American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Physics of Fluids 32, 044105 (2020); https://doi.org/10.1063/5.0001914 and may be found at https://doi.org/10.1063/5.0001914
Identifier
https://aip.scitation.org/doi/10.1063/5.0001914
Subjects
Fluids & Plasmas
01 Mathematical Sciences
02 Physical Sciences
09 Engineering
Publication Status
Published
Article Number
044105
Date Publish Online
2020-04-17