Dynamic Calibration of a Shear-Stress Sensor by Acoustic Waves – APS Division of Fluid Dynamics Nov 1996

Many important fluid mechanics phenomena are dominated by turbulent wall-shear, yet continuous, fluctuating wall-shear data can only be obtained by indirect methods (e.g., thin-film anemometry). Recently, silicon micromachining technology has produced a miniature, floating-element shear-stress gauge which directly measures fluctuating wall shear(Padmanabhan, A., et al.), AIAA Paper 96-0422.. Static calibrations demonstrate the linearity of this device over a broad measurement range and spectra indicate a bandwidth in excess of 10 kHz. However, the actual characteristics of the frequency response function, however, are presently unknown and thus, in order to use this device to obtain quantitative turbulence information, the effects of the inherent mass, compliance, and damping of the floating-element structure on the dynamic response must be characterized. To elucidate these effects, an acoustic plane wave generator capable of providing a sinusoidal shear input to the sensor was developed. In this calibration technique, the sinusoidal shear stress is inferred from the cylindrical Stokes’ layer solution for a plane acoustic wave. The theoretical aspects of this technique will be discussed and preliminary results presented.

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