Dynamic calibration technique for the micro-pillar shear-stress sensor MPS3

Based on magnetic excitation a dynamic calibration technique for the micro-pillar shear-stress sensor MPS3, which allows one to determine the local wall-shear stress in turbulent flows by optically measuring the velocity gradient within the viscous sublayer of turbulent flows, is described. The proposed dynamic calibration technique allows one to assess the micro-pillar dynamic response for different flow media up to approximately 10 kHz. The results convincingly agree with the findings of a second-order analytical approximation based on experimentally determined damped eigenfrequencies and damping coefficients. Measurements for different sensor geometries and in various fluids show the sensor to possess transfer functions ranging from a flat low-pass filtered response to strong resonant behavior.