Visualization and Detection of Wall Shear Stress using Micro Shear Stress Sensor and Discrete Wavelet Analysis

Abstract

Shear stress stripe structure on the wall in turbulent boundary layer has been clearly visualized by a combination of a shear stress sensor using MEMS (Micro-Electro-Mechanical-Systems) and discrete wavelets transform. The MEMS shear stress micro chip is designed and fabricated by surface micro-machining technology, contributing to obtaining the time-space two dimensional shear stress data. One array of 25 micro shear stress sensors in the chip that covers a length of 7.5mm is used to measure the instantaneous spanwise distribution of the surface shear stress. The discrete wavelets transform is a software technique to decompose the frequency level with the time and space information of the wave form. In details, the structure in lower Reynolds number is shown clearly on lower frequency wavelets level, the structure in high Reynolds number is done clearly on higher frequency wavelets level. To visualize and detect the high shear stress area more clearly, the frequency levels are recomposed using the multiresolution filtering effect of wavelets transform. The experiments for the shear stress distribution were carried out on Re=8700 and 17400.