Abstract:
Attenuation of flow-induced pseudonoise from the pressure signal of a microphone placed in a flow field was experimentally performed by coupling the output from a hot-wire anemometer with that of the microphone (called a hot-mic for brevity). A pinhole microphone and a hot-wire sensor located just upstream of the pinhole opening were placed in a well-defined, low-speed turbulent flow in a rectangular duct. Controlled acoustic noise, both random and time harmonic, was superimposed on the flow noise by aspeaker source located near the entrance of the duct. Experiments proved that significant flow-noise attenuation is achievable by adaptively filtering the hot-wire signal using a least-mean-square algorithm before subtracting it from the microphone signal. Broadband flow noise is attenuated 20 dB or more at frequencies below 100 Hz and the resulting hot-mic spectra more closely resemble those of the uncontaminated microphone over an even greater frequency range. Moreover, the resulting signal from the hot-mic retains the acoustic pressure information of interest, making the hot-mic an ideal ``sensor`` for use in active noise control applications where the sensing or error microphone must be placed in a flow field. [Work sponsored by the United Technologies Research Center.]