Analysis of dynamic images based on wavelet transform in a hypersonic boundary layer
Yan Tao Tian · Journal of Experiments in Fluid Mechanics · 2009
The photographs of hypersonic boundary-layer transition experiments were investigated on a dynamic sharp cone in periodic pitching swing by using 2-D wavelet transform technique.The methods of denoising and enhancing image based on wavelet transform were presented to optimize the dynamic images and extract the outline of sharp cone and graphics of boundary layer according to the singularity of wavelet images,thereby the pitching swing periods and angels of attack were calculated.The results indicate that there is a phase difference between the periodically alterative thickness of the boundary layer and the periodic swing of sharp cone.Furthermore,the point of transition on leeward wall of sharp cone moves onward to the foreside of the sharp cone.The experiment shows that the technique of image process based on wavelet transform can not only qualitatively visualize the flow in hypersonic boundary layer,but also accurately measure and quantitatively analyze hypersonic boundary layer transition images,which becomes a qualitatively and automated experimental technique and analytical method.