Calibration Analysis And Examination Tests Of MEMS Wall Shear Stress Sensor For Under-Water Application

Accurate measurement of wall shear stress is both important for drag reduction and turbulence structure research, however it is hard to be measured precisely with traditional wall shear stress sensor. In recent years, MEMS hot-film wall shear stress sensor which combines MEMS technique and traditional hot-film technique received widely attention. It has the advantages of high frequency response and high resolution. In order to realize practical applications of under-water measurements, some efforts are made in this paper to analyze the calibration of MEMS hot-film wall shear stress sensor and conduct flat plate tests for further examination.Under-water calibration is carried out in a precision water tunnel. The wall shear stress is obtained through pressure gradient measurement. Calibration curve is acquired through collections and analyses of wall shear stress input and voltage output under different working conditions. Uncertainty analyses of wall shear stress measurement and voltage measurement are given through duplicated measurements. Results show that the calibration equation is reliable and the MEMS sensor can be used to application with desirable accuracy.Wall shear stress of flat plate boundary layer is measured with the calibrated MEMS sensor and also determined from the fitting of velocity profile obtained with LDV(Laser Doppler Velocimetry)method. Empirical equation estimation of wall shear stress is performed too. Through comparison, it can be seen that the three agree well with each other with bias no more than 5%. It can be concluded that MEMS calibration result is valid and MEMS method can be applied into wall shear stress measurement reliably.