The secondary instabilities of stationary cross-flow vortices in a Mach 6 swept wing flow

Xu, Guangrui; Chen, Jianqiang; Liu, Gang; Dong, Siwei; Fu, Song

doi:10.1017/jfm.2019.397

Cited by 34 publications

(16 citation statements)

References 36 publications

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“…[15], the large frequency bandwidth of this mode appears consistent as it lies in the relatively thin, inclined shear layer associated with the overturning contours of axial velocity from the strong crossflow vortex. Its shape and location are similar to the 'z' mode obtained in previous stability studies in swept-wing three-dimensional boundary layers [32]. The phase speed of each mode is shown in Fig.…”

Section: B Linear Instabilities Of the Roughness Wakesupporting

confidence: 76%

Roughness-Induced Instabilities and Transition on a Generic Hypersonic Forebody at Mach 6

et al. 2021

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In hypersonic flows, it is often necessary to be able to trip the transition to turbulence, upstream of air intakes for example. Direct numerical simulations have been performed to identify the roughness-induced transition mechanisms on a wedge-like forebody at Mach 6 and unit Reynolds number Re = 11 million (/m). Good agreement with the experiments performed in the Boeing/AFOSR Mach-6 Quiet Tunnel (BAM6QT) at Purdue University was obtained in terms of wall heat flux and wall pressure fluctuations. First, an isolated roughness was considered. The presence of the roughness in the span-inhomogeneous base flow leads to the formation of a crossflow-like vortex. High-frequency secondary instabilities of the stationary crossflow vortex are observed in the wake and are found to be responsible for the breakdown to turbulence. Spatial linear modal instability analysis of this flow has been performed at selected streamwise locations. The linear stability approach is found to give accurate predictions in terms of mode shapes, most amplified disturbance frequencies and growth rates, as it only underpredicts the N-factor of the most unstable mode by 10% compared to the direct numerical simulations. Unsteady simulations were then carried out for a trip array configuration and showed that it does not change the transition mechanisms, but the frequencies of the most unstable secondary instabilities were found to be higher. Nomenclature

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Section: B Linear Instabilities Of the Roughness Wakesupporting

confidence: 76%

Roughness-Induced Instabilities and Transition on a Generic Hypersonic Forebody at Mach 6

et al. 2021

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“…The swept wing is modelled by a swept parabolic body, which was widely adopted in previous investigations concerning cross-flow instability (see Mack & Schmid 2010; Xu et al. 2019; Xi et al. 2021).…”

Section: Problem Description and Governing Equationsmentioning

confidence: 99%

“…Recently, combined NPSE, SIT and DNS investigations were performed by Xu et al. (2019) and Chen et al. (2021 a ) for the flow over a Mach-6 swept parabola.…”

Section: Introductionmentioning

confidence: 99%

Cross-flow vortices and their secondary instabilities in hypersonic and high-enthalpy boundary layers

Chen

Ren

et al. 2022

J. Fluid Mech.

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Compared to the streamwise instability, the cross-flow instability in high-enthalpy flows has received relatively less attention, but the latter is of vital importance in the flow transition for practical configurations. This work aims to investigate the cross-flow primary and secondary instabilities in hypersonic and high-enthalpy boundary layers, considering thermochemical non-equilibrium (TCNE) effects. The numerical tools adopted include a high-order shock-fitting solver, nonlinear parabolized stability equations and secondary instability theory (SIT). The flow over a swept parabola is calculated at a free-stream Mach number of 16. It is found that TCNE has a destabilizing effect on the cross-flow mode with a non-catalytic wall. Two important non-dimensional parameters are summarized to explain this effect. One is the ratio between the wall and boundary-layer edge temperatures, and the other is the cross-flow Mach number. Due to nonlinear effects, the stationary cross-flow vortices evolve and exhibit the classic rollover structures as in lower-speed flows. Two different disturbance energy norms are used in the energy budget analysis to classify the secondary cross-flow instability modes. The results from SIT highlight the importance of type-IV modes in TCNE flows at the downwash region of the vortex. The type-IV modes arise with the combined contribution from the wall-normal (on top and trough of the vortex) and spanwise (in the downwash region) production terms. The type-I mode is dominant in the calorically perfect gas case with an adiabatic wall, whereas the type-IV mode has the largest growth rate in the TCNE cases irrespective of wall temperature variation.

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“…[1][2][3]), especially in hypersonic conditions. Therefore, in the last decades, considerable efforts have been made towards building a fundamental understanding to the transition of hypersonic three-dimensional boundary layers by wind tunnel experiments [4][5][6][7][8][9], theoretical analyses [10][11][12][13], direct numerical simulations (Chen et al: Transition of hypersonic boundary layer over a yawed blunt cone, submitted) (Chen et al: Stationary cross-flow breakdown in a high-speed swept-wing boundary layer, submitted) and flight tests (see overview [14]). Nevertheless, much is still unknown.…”

Section: Introductionmentioning

confidence: 99%

“…A typical example is the breakdown of crossflow vortices. In both the low-and high-speed flows with crossflow, it has been found that the z-type (produced by the spanwise or azimuthal gradients of the streamwise mean flow) secondary crossflow instability is responsible for the natural transition process [17] (Chen et al: Stationary cross-flow breakdown in a high-speed swept-wing boundary layer, submitted), although stability analyses [13,17] also detected the y-type (produced by the wall-normal gradient of the streamwise mean flow) secondary crossflow instabilities.…”

Section: Introductionmentioning

confidence: 99%

Wall pressure beneath a transitional hypersonic boundary layer over an inclined straight circular cone

et al. 2020

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Properties of wall pressure beneath a transitional hypersonic boundary layer over a 7∘ half-angle blunt cone at angle of attack 6∘ are studied by Direct Numerical Simulation. The wall pressure has two distinct frequency peaks. The low-frequency peak with f≈10−50 kHz is very likely the unsteady crossflow mode based on its convection direction, i.e. along the axial direction and towards the windward symmetry ray. High-frequency peaks are roughly proportional to the local boundary layer thickness. Along the trajectories of stationary crossflow vortices, the location of intense high-frequency wall pressure moves from the bottom of trough where the boundary layer is thin to the bottom of shoulder where the boundary layer is thick. By comparing the pressure field with that inside a high-speed transitional swept-wing boundary layer dominated by the z-type secondary crossflow mode, we found that the high-frequency signal originates from the Mack mode and evolves into the secondary crossflow instability.

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The secondary instabilities of stationary cross-flow vortices in a Mach 6 swept wing flow

Cited by 34 publications

References 36 publications

Roughness-Induced Instabilities and Transition on a Generic Hypersonic Forebody at Mach 6

Roughness-Induced Instabilities and Transition on a Generic Hypersonic Forebody at Mach 6

Cross-flow vortices and their secondary instabilities in hypersonic and high-enthalpy boundary layers

Wall pressure beneath a transitional hypersonic boundary layer over an inclined straight circular cone

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