Measurement of the Transfer Function of Hot-Wire and Hot-Film Turbulence Transducers

A microwave simulator for controlled variation of air-flow velocity in the dc to 500 kHz frequency range is described. The simulator serves for measurement of the transfer function of hot-wire and hot-film transducers used in turbulence research. The microwave simulator consists of an X-band power modulated klystron which delivers electromagnetic energy to the transducer, mounted in a small-size calibration wind-tunnel supplying the transducer mean flow velocity (in the 0 to 80 m/s range). Experimental results are given for the absolute value of the transfer function in a 60 dB range, of a hot-wire tungsten transducer (5 micron diameter X 1 mm long) and of a platinum-plated quartz hot-film transducer (25 micron diameter × 0.5 mm long).