熱パルスによる低風速の測定

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A pulsed-wire anemometer was developed for low velocity air flow down to 0.2m/s, which consists of a pulsed heating wire and two sensor wires, both being set down-stream. The current of the pulsed wire is electronically controlled so that a tracer of heated air has a spatially symmetric temperature distribution particularly around the maximum-temperature point when observed from the moving coordinate system. The velocity is detected from the time delay given by the maximum temperatures between the two sensor wires. This method is considered as a developed form of the pulsed-wire method originally informed by Bauer et al. or a developed form of the stationary heated-Wake metnhod by Kovasznay et al.Application of Bauer's method to the low velocity flow faces the difficulties caused by the variation of temperature distribution in the heated tracer due to the thermal diffusion, the error in detecting the moving tracer with a varying temperature distribution at the two separated-fixed points, and the time delay of detecting due to the heat capacity of the sensor. These difficulties were solved by the use of controlled heating current and the detection of the maximum, temperatures by two sensors.The waveform of the heating current pulse was theoretically and numerically analyzed in order to obtain heated tracer air With a symmetric temperature distribution at and above half the maximum temperature. Experimental investigation was made in the air flow using a wind tunnel of which the cross section is 70×140mm. The velocity investigated by this method ranges from 0.2m/s to 1.2m/s. Compared with the differential pulsed-wire method by Bradbury et al., the proposed method was shown to extend the measurement capability in the low velocity range.