311 Basic Research on the Acoustic Analysis of a Duct by Using the Scattering Matrix Method

Sougawa, Hidenori; Nishimura, Masaharu; Kudo, Toshifumi

doi:10.1299/jsmedmc.2007._311-1_

Cited by 1 publication

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“…Therefore, an assessment method to predict the acoustic resonance in the model wind tunnel is necessary. There are several simulation methods based on one-dimensional analysis, such as the transfer matrix method (12-13), the normal mode method (14), and the scattering matrix method (15). Here, the scattering matrix method was selected because it is the only method that can be applied to a closed circuit such as a wind tunnel.…”

Section: Analysis Of the Acoustic Opening Using Scattering Matrix Methodsmentioning

confidence: 99%

“…In addition, f i and g i are particle velocities in opposite directions at the boundary between each pair of elements, f s (i) and g s (i) are the particle velocities generated in each element, p i and u i are the acoustic pressure and absolute particle velocity at the boundary between each pair of elements, and ρ i and c i are the density and acoustic speed of the fluid in each element, respectively. Then, the coefficients of each scattering matrix were calculated by Equations 2 and 3 using the coefficients of the transfer matrices (15). In the case of a simple pipe (Equation 4), the particle velocities f 1 , g 1 , f n+1 , and g n+1 are related to each other through the reflection coefficients r ue and r de at the ends of the pipe.…”

Section: Appendixmentioning

confidence: 99%

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Techniques for Reducing Low-Frequency Fluctuations in Aeroacoustic Wind Tunnels

Kudo

Komatsu

Maeda

et al. 2009

JEE

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Aeroacoustic wind tunnels, which consist of large measuring sections, such as anechoic rooms, and open jets, are generally applied as test facilities to measure aerodynamic noise generated around vehicles. In aeroacoustic wind tunnels, it is easy to generate flow-induced low-frequency fluctuations resulting in pressure fluctuations or velocity fluctuations associated with vortices or turbulence in the open jet. These low-frequency fluctuations are generated by various flow-induced phenomena, such as swaying that occurs in various elements of the circuit, fluctuations propagated from the shear layers or mixing layers of the open jet, and the acoustic resonances of the whole circuit, which often become serious problems, generally called pulsations, at particular wind speeds. Because these low-frequency fluctuations may affect the measured pressure and velocity of a flow around vehicles in measuring sections, we should aim to reduce or control them when designing aeroacoustic wind tunnels to ensure measurement with high reliability. In this study, we investigate the generating mechanisms and techniques for reducing these low-frequency fluctuations in aeroacoustic wind tunnels by performing experiments on a model wind tunnel. In particular, new techniques for reducing acoustic resonance components such as by installing an acoustic opening in the circuit are proposed and verified by simulations and experiments. Using these techniques for reducing low-frequency fluctuations, the fluctuations of pressure and velocity in the measuring section are markedly decreased over the entire wind speed range.

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Section: Analysis Of the Acoustic Opening Using Scattering Matrix Methodsmentioning

confidence: 99%

Section: Appendixmentioning

confidence: 99%