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Highly separated axisymmetric step shock-wave/turbulent-boundary-layer interaction

Published online by Cambridge University Press:  06 September 2017

Gaurav Chandola ,
Xin Huang  and
David Estruch-Samper Open the ORCID record for David Estruch-Samper [Opens in a new window]
Gaurav Chandola
Affiliation:
Department of Mechanical Engineering, National University of Singapore, 117575, Singapore
Xin Huang
Affiliation:
Department of Mechanical Engineering, National University of Singapore, 117575, Singapore
David Estruch-Samper*
Affiliation:
Department of Mechanical Engineering, National University of Singapore, 117575, Singapore
*
†Email address for correspondence: mpedavid@nus.edu.sg
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Abstract

The unsteadiness of a shock-wave/turbulent-boundary-layer interaction induced by an axisymmetric step (cylinder/$90^{\circ }$-disk) is investigated experimentally at Mach 3.9. A large-scale separation of the order of previously reported incoming turbulent superstructures is induced ahead of the step ${\sim}30\unicode[STIX]{x1D6FF}_{o}$ and followed by a downstream separation of ${\sim}10\unicode[STIX]{x1D6FF}_{o}$ behind it, where $\unicode[STIX]{x1D6FF}_{o}$ is the incoming boundary-layer thickness. Narrowband high-frequency instabilities shift gradually to more moderate frequencies along the upstream separation region exhibiting a strong predominance of shear-induced disturbance levels – arising between the outer high-speed flow and the subsonic bubble. Through spectral/time-resolved analysis of this high Reynolds number and large-scale separation, results offer new insights into the shear layer’s inception and evolution (convection, growth and instability) and its influence on interaction unsteadiness.

JFM classification

Boundary Layers: Boundary layer separation Aerodynamics: High-speed flow Compressible Flows: Shock waves
Type
Papers
Information
Journal of Fluid Mechanics , Volume 828 , 10 October 2017 , pp. 236 - 270
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Copyright
© 2017 Cambridge University Press 

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Chandola et al. supplementary movie 1

High-speed schlieren corresponding to figure 7b and played at a rate of: t/To=1 (top), t/To=10 (bottom left) and t/To=100 (bottom right) per second in the video, where To is the characteristic timescale of upstream bubble pulsations. For h/δo=5.9 step at Me=3.9 and Ree= 6.1x107m-1(fo= 391 Hz). White square indicates region of interest considered in movie 2.

Download Chandola et al. supplementary movie 1(Video)
Video 123.6 MB

Chandola et al. supplementary movie 2

Highly separated axisymmetric step STBLI (left) with schlieren-based correlation between upstream separation shock displacement xson the top φ=0o and bottom of the image φ=180o (top right) and variation of respective shock displacement ΔxU* with time, where ΔxU*=(xs−xs,av)/L (bottom right). Played consecutively at (a) t/To=1, (b) t/To=10 and (c) t/To=100 per second in the video, with correlation plot populated with time. Joint probability density function (PDF) contour levels are shown at the end, with poor correlation at low frequencies between opposite sides (1kHz low-pass filter). Note: total test window duration of 5.24s covers an equivalent of 2050To (Ue/δo=0.94x106).

Download Chandola et al. supplementary movie 2(Video)
Video 63.9 MB