An integrated pressure-flow sensor for correlation measurements in turbulent gas flows

A new integrated pressure-how sensor has been specially designed for measurements in turbulent gas flows. The pressure sensor is based on polysilicon diaphragm technology and the flow sensor on the gas cooling of a polyimide-insulated heated mass. With a pressure-sensor diaphragm area of 100 mu m X 100 mu m, a flow-sensor hot-chip area of 300 mu m X 60 mu m and an edge-to-edge distance of 100 mu m between the different sensor areas, the smallest eddies in technically interesting turbulent flows can be resolved and measured. The pressure sensor design shows a flat frequency response curve within +/-2 dB between 10 Hz and 10 kHz with an acoustic sensitivity of 0.9 mu V Pa-1 for a supply voltage of 10 V. The flow sensor has a thermal response with a time constant of 7 ms and a response time of 25 mu s when the sensor is operated at constant temperature using feedback electronics. The measured steady-state flow-sensor power dissipation in a turbulent wall boundary sensor has been used for simultaneous measurement of fluctuating pressure and wall shear stress in a turbulent boundary layer yielding pressure-wall shear stress correlation coefficients never previously presented.