Second mode unstable disturbance measurement of hypersonic boundary layer on cone by wavelet transform |
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Authors: | Jian Han Nan Jiang Yan Tian |
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Institution: | (1) von Karman Institute for Fluid Dynamics, Rhode-St-Genèse, Belgium; |
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Abstract: | Experimental investigation of hypersonic boundary layer instability on a cone is performed at Mach number 6 in a hypersonic
wind tunnel. Time series signals of instantaneous fluctuating surface-thermal-flux are measured by Pt-thin-film thermocouple
temperature sensors mounted at 28 stations on the cone surface in the streamwise direction to investigate the development
of the unstable disturbance. Wavelet transform is employed as a mathematical tool to obtain the multi-scale characteristics
of fluctuating surface-thermal-flux both in the temporal and spectrum space. The conditional sampling algorithm using wavelet
coefficient as an index is put forward to extract the unstable disturbance waveform from the fluctuating surface-thermal-flux
signals. The generic waveform for the second mode unstable disturbance is obtained by a phase-averaging technique. The development
of the unstable disturbance in the streamwise direction is assessed both in the temporal and spectrum space. Our study shows
that the local unstable disturbance detection method based on wavelet transformation offers an alternative powerful tool in
studying the hypersonic unstable mode of laminar-turbulent transition. It is demonstrated that, at hypersonic speeds, the
dominant flow instability is the second mode, which governs the course of laminar-turbulent transition of sharp cone boundary
layer. |
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Keywords: | Hypersonic boundary layer Sharp cone Instability Wavelet transform |
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