Calibration of a thermal MEMS shear stress sensor array

Abstract

Accurate measurement of wall shear stress is very important for understanding wall bounded shear flows properly, because it provides significant information about the flow phenomena, including viscous drag, the position where the flow transits to turbulence or separates from the model. Current measurement of shear stresses based on traditional fabrication technology are much too bulky to accomplish the task perfectly and may destroy the research matrix surface and most likely impossible to be used in any large-scale integration. The conflict between sensor size and sensitivity is the maximal impedance to the advancement. So making the sensor smaller flexible with high time resolution can bring the boundary layer research to a new horizon. One way of achieving these requirements is micro-fabricated sensors. This paper presents that by taking advantage of MEMS fabrication techniques, sensors can response very quickly to the fluctuations in the flow and do not destroy the model surface. Then, combining an integrating technology, plenty of sensors can be integrated to a membrane for measuring the wall shear stress in larger area simultaneously. The characterization of a MEMS based thermal shear stress sensor array for high speed flow is presented in this paper. The static responses for different overheat ratios were obtained via a fully developed duct flow with Ma number 0.1~0.6, and the influence of temperature to the sensor output voltage was measured using a heater with four resistance coils which is able to change the flow temperature of the test section from 289~313K. The relationship between the output voltage and shear stress at overheat ratio of 1.2 is calculated. According to that above, calibration methods is very key technique for application of MEMS sensors on flow measurement in high speed wind tunnel. Therefore, the method can provide useful help for application and development of MEMS sensors.