The dynamic behaviour of hot-wire anemometers with conduction end losses

Abstract

A theoretical analysis is presented of the dynamic behaviour of hot-wire anemometers subject to small harmonic fluctuations in flow properties, when conduction end losses to the probe supports are not negligible. Both constant temperature and constant current instruments are considered, as are fluctuations in both heat transfer coefficient and adiabatic recovery temperature. The analysis is valid for arbitrary support temperature and can thus be applied to the case of supersonic rarefied flows where the adiabatic recovery temperatures of the probe wire and the supports may not be equal. The dynamic response of the constant temperature anemometer at different frequencies is described in terms of a complex parameter, the modulus and argument of which have been calculated for a range of variables covering all possible probe conditions. It is found that the argument is small (always less than 12 degrees ) so that for most practical purposes the parameter may be taken to be real, with considerable simplification. A complete probe calibration scheme, including dynamic effects, is described.