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High Reynolds number turbulent wind tunnel boundary layer wall-shear stress sensor

The fluctuating wall-shear stress in a turbulent zero-pressure gradient wind tunnel boundary layer at high Reynolds numbers up to Re Θ = 11,400 is determined by the micro-pillar shear-stress sensor MPS3. The sensor concept has already successfully been applied to liquid fluid flows, where the sensor shows low-pass filter characteristics. The low-pass filter characteristic is favorable especially when turbulent frequencies larger than the damped eigenfrequency of the structure occur. The application in air, however, is critical since the dynamic transfer function of the sensor structures exhibits a strong resonance due to low damping. The current results demonstrate that as long as frequencies of turbulent wall-shear stress fluctuations are below the damped eigenfrequency even a resonant sensor structure can be used to accurately assess the fluctuating wall-shear stress, e.g., in turbulent wind tunnel boundary layers.