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Title: Mechanism of stabilization of porous coatings on unstable supersonic mode in hypersonic boundary layers
Authors: Long, T 
Dong, Y
Zhao, R
Wen, C 
Issue Date: May-2021
Source: Physics of fluids, May 2021, v. 33, no. 5, 054105
Abstract: This study clarifies the fundamental mechanism by which porous coatings suppress the supersonic mode instability in the hypersonic boundary layer (BL) by using Doak's momentum potential theory. The independent energy budget equations for vortical, acoustic, and thermal components of instabilities are derived. Data from direct numerical simulations of Mach 6.0 flat plate flows on a solid wall and porous coatings are then analyzed. By decomposing the momentum density into vortical, acoustic, and thermal components, the source terms and fluxes are studied based on their corresponding energy corollaries. The results demonstrate the role of different components in the generation and transport of the total fluctuation enthalpy (TFE) and the way in which the fluctuation energy is transferred between components. In the case of the solid wall, the oscillating disturbance on the BL consists of acoustic and vortical components. Near the critical layer, the positive acoustic source and energy transferred from the vortical component are primary energy producers for acoustic fluxes. Then, the TFE is transported outward by the acoustic component, which leads to “sound radiation” in the supersonic mode. In the case of the porous coating, the positive vortical source near the surface of the plate is suppressed significantly. Less vortical energy is transported to the critical layer, and thus less vortical energy is transformed into acoustic energy. Acoustic energy is eventually exhausted due to energy loss in the outward transport of the TFE, and “sound radiation” disappears from the porous coating.
Publisher: American Institute of Physics
Journal: Physics of fluids 
ISSN: 1070-6631
EISSN: 1089-7666
DOI: 10.1063/5.0048313
Rights: © 2021 Author(s).
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Long, T., Dong, Y., Zhao, R., & Wen, C. (2021). Mechanism of stabilization of porous coatings on unstable supersonic mode in hypersonic boundary layers. Physics of Fluids, 33(5), 054105.and may be found at
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