The dynamic response of a hot-wire anemometer: IV. Sine-wave voltage perturbation testing for near-wall hot-wire/film probes and the presence of low-high frequency response characteristics

Experiments were performed using the electronic sine-wave voltage-perturbat ion test to systematically study the frequency responses of near-wall hot-w ire probes subjected in turn to varying magnitudes of convective velocity a nd different effects of wall influence. In addition, qual ta-substrate hot- film gauges with various thicknesses of quartz coating were also investigat ed. Results of the high cut-off frequency obtained using the sine-wave test (f(sine)) were found to be in fair agreement with those obtained using the square-wave test (f(S)) both for hot-wire and for hot-film sensors. The si ne-wave test response curve exhibited a distinct bulging effect for the hot -film gauges. For the hot-wire sensors, a much weaker bulging effect was al so observed, In contrast to f(S) and f(sine), the low frequency response ch aracteristic corresponding to the location of the bulging effect (f(bulge)) compared much more favourably with the dynamic frequency response (f(D)) o btained by Khoo et al and Chew et al using a known near-wall fluctuating fl ow field. Freymuth's theory for non-cylindrical hot-film sensors incorporat ing the Bellhouse-Schultz model was applied to predict the responses of the hot-film wall gauges when they were subjected to electronic sine-wave test ing and dynamic perturbation testing under different parametric conditions. Although it is one-dimensional in nature, the model is capable of predicti ng most of the trends observed in the present study and previous works by K hoo ct al (1998a) and Chew er nl (1998a).