Experimental Investigations Of Hypersonic Boundary Layer Transition On A Sharp Cone Based On The Method Of Wavelet Analysis

The investigation of laminar-turbulent transition is the most challenging task in the area of modern fluid dynamics, and it is crucial importance in the design of modern high-performance aerodynamic vehicles. An experiment had been devoted to learn more about the characters in the transition process. A model of a 5-degree half-angle sharp cone was tested in a hypersonic tunnel at free-stream Mach number 5.95. The wall pressure and wall temperture have been measured at angle of attack 0-degree and a range of Reynolds numbers(stagnation pressure P0≈690;980;1430KPa). Also the heat flux fluctuating wall characters of boundary layer have been meansured finely by the ALTP at the same time. The signals of heat flux fluctuating wall characters of boundary layer which were abtained by ALTP have been investigated using the wavelet analysis. Also the power spectrum and bispectrum and cross-bispectrum which are based on the wavelet analysis have been investigated.In the study of basic hypersonic flow characters, the states of basic flow were identified at different Reynolds numbers and the laminar-turbulent transition process was observed when the stagnation pressure P0≈1430KPa. The first-mode disturbance and the second-mode disturbance were observed clearly in the wavelet analysis and power spectrums'computation of the heat flux fluctuating signals. And whether the first-mode disturbance or the second-mode disturbance is the most dominant can not be decided when the transition process does not occur(P0≈690;980KPa), but in the transition process(P0≈1430KPa) the second-mode instability is the most dominant absolutely and the first-mode disturbance becomes indistinctly. The coupling mechanisms of the every frequency in the signals were discussed through the bispectrums'and cross-bispectrums'investigations. The scenes of the fist-mode or the second-mode which was the most dominant were identified clearly in the bispectrums'study, and this conclusion was consistent with the wavelet analysis and the power spectrums'computation. In the bispectrums'study, the intensive interactions between the two characteristic frequencies that are nearly have been discovered, and the region of interaction enlarged with the frequencies'increased. The results of the cross-bispectrums'study show that although there are nonlinear coupling interactions between every frequency, the effect on the other frequency that is relatived them in a hypsonic flow is slightly. In the investigations of this dissertation, wavelet transformation techniques are used to provide a new insight into the characters'identification of the fist-mode disturbance and the second-mode disturbance in a hypersonic flow. And the investigations of the power spectrum, bispectrum and cross-bispectrum which are based on the wavelet transformation show that more profound understanding about the characteristic-modes'interaction.