MEMS for aerodynamic control

Abstract

Multiple arrays of micromachined micro shearstress sensors have been designed and fabricated to spatially and temporally resolve the small streamwise streaks in the near-wall region of a turbulent boundary layer. By using these sensors, the instantaneous surface shear-stress distribution of a turbulent boundary layer at high Reynolds numbers has been measured. Based on the measurement, the physical quantities associated with the high shear-stress streaks, such as their length, width and peak shear-stress level, are obtained. We found that a high correlation exists between the peak shear stress level and the front-end shear-stress gradient of a high shear-stress streak. This important property is currently being applied to the design of a real-time flow control logic. The control logic will be used to initiate a micro actuator, which interacts with the detected streak for the purpose of reducing local shear stress. The interaction between an actuator with near wall vortices was first investigated in a laminar boundary layer. The results show that the level of reduction is related to the product of the actuator's peak amplitude and oscillating frequency. This result suggests the possibility of achieving shear-stress reduction by using high-frequency and low-amplitude actuators.