Abstract
The mechanism of turbulence amplification in shock-wave/boundary layer interactions is reviewed, and a new turbulence amplification mechanism is proposed based on the analysis of data from direct numerical simulation of an oblique shock-wave/flat-plate boundary layer interaction at Mach 2.25. In the upstream part of the interaction zone, the amplification of turbulence is not essentially shear driven, but induced by the interaction of the deceleration of mean flow with streamwise velocity fluctuations, which causes a rapid increase of turbulence intensity in the near-wall region. In the downstream part of the interaction zone, the high turbulence intensity is mainly due to the free shear layer generated in the interaction zone. During the initial stage of turbulence amplification, the characteristics of wall turbulence, including compact velocity streaks, streamwise vortices and an anisotropic Reynolds stress, are well preserved. The mechanism proposed explains the high level of turbulence in the near-wall region observed in some experiments and numerical simulations.
Highlights
The amplification of turbulence is a key feature in shock-wave/turbulence interaction (SWTI) and shock-wave/turbulent boundary layer interaction (SWTBLI), which is closely connected to flow separation, wall heat flux peak, skin friction and acoustic radiation in high-speed flows
Based on the above analysis, we identify the interaction zone upstream of the foot of the impinging shock wave as the deceleration zone, where the production of turbulence is mainly due to the deceleration of the mean flow
The amplification of turbulence in an oblique shock-wave/flat-plate boundary layer interaction is studied by analysing direct numerical simulation (DNS) data
Summary
The amplification of turbulence is a key feature in shock-wave/turbulence interaction (SWTI) and shock-wave/turbulent boundary layer interaction (SWTBLI), which is closely connected to flow separation, wall heat flux peak, skin friction and acoustic radiation in high-speed flows. In the early stage (1950s–2000s), many factors (e.g. unsteady shock-wave movement, direct shock-wave/turbulence interaction, generation of acoustic and entropy waves and a free shear layer) were considered to make contributions to the turbulence amplification, but the key factor could not be identified In the latter stage (2000s–present), due to the application of advanced experimental technologies (e.g. particle image velocimetry) and high-fidelity simulations (e.g. DNS and large-eddy simulation) in the research of high-speed flow, some less important factors were excluded, and the free shear layer was believed to be the key factor for the amplification of turbulence, based on the observation that the maximum turbulence energy and turbulence kinetic energy production are located far away from the wall.
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