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

A new integrated pressure—flow 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 μm × 100 μm, a flow-sensor hot-chip area of 300 μm × 60 μm and an edge-to-edge distance of 100 μm 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 μV 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 μs when the sensor is operated at constant temperature using feedback electronics. The measured steady-state flow-sensor power dissipation in a turbulent wall boundary layer at an overtemperature of 100 °C was P = 34 + 0.4τ00.47 mW where τ0 is the time-average flow-dependent wall shear stress. The integrated 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.