Acoustics and experimental methods: The influence of sound on flow and heat transfer

• Published in: Experimental thermal and fluid science 1990, Vol.3 (1), p.138-152
• Main Authors: Welsh, M.C., Hourigan, K., Welch, L.W., Downie, R.J., Thompson, M.C., Stokes, A.N.
• Format: Article
• Language: English
• Subjects: acoustics; measurement techniques; separated flow; sound and flow; sound and heat transfer
• ISSN: 0894-1777; 1879-2286
• DOI: 10.1016/0894-1777(90)90106-H

The influence of sound on the type of experimental methods used in flow and heat transfer test rigs is discussed. The type of acoustic mode that interacts most readily with the flow is described. When solid walls are present in the working section of test rigs and wind tunnels, acoustic modes can readily be excited in the working sections without the knowledge of experimenters and can lead to an erroneous interpretation of test results. Examples of the interaction between loud sounds, up to 150 dB, and the flow are described. These sounds can be generated by the flow, but in general they are easily detected since they are heard by the experimenter and alter the flow and the heat transfer characteristics in a very obvious manner. Recent experiments at CSIRO show that sound levels between 70 and 95 dB (with corresponding ratios of the velocity due to sound to the freestream velocity of between ∼ 0.0001 and ∼ 0.002) generated by the flow can alter both the flow and the heat transfer characteristics in a manner not immediately obvious to the experimenter. Consequently, a microphone should always be located in the working section of a wind tunnel with the test model installed so that unwanted sound can be detected. Methods of canceling the unwanted sound in wind tunnels and test rigs are also presented.