Validation of laser Doppler anemometer measurements of power dissipation in an arbitrary termination

Abstract

The two-microphone technique is commonly used to measure power dissipation in arbitrary acoustic terminations. This method is well established and provides reliable results when care is taken to avoid problematic microphone configurations (e.g., a pressure node at a microphone location or the microphone spacing being too small in comparison to the wavelength). A laser Doppler anemometer (LDA) technique of measuring power dissipation is discussed in this paper. The LDA method has several disadvantages over microphone methods, including cost of the equipment, the need to use periodic test signals, the need for tracer particles, and the need for a transparent pipe. However, rather than being limited to fixed microphone locations and working under the plane wave assumption, the LDA method allows measurement of multiple components of the velocity field at numerous locations with arbitrary spacing in three dimensions. The purpose of this paper is to validate the LDA method by measuring the power dissipated in a variable RC load connected to one end of the pipe. [Fusco and Ward, J. Acoust. Soc. Am. 91, 2229-2235 (1992)]. The measured result agrees to within 0.8% for the power dissipated in the RC load. [Work supported by the Penn State Graduate Program in Acoustics.]