Experimental visualization of aerodynamic sound sources using parallel phase-shifting interferometry
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Experimental visualization of aerodynamic sound sources using parallel phase‑shifting interferometry Risako Tanigawa1 · Kohei Yatabe1 · Yasuhiro Oikawa1 Received: 15 January 2020 / Revised: 24 July 2020 / Accepted: 19 August 2020 © The Author(s) 2020
Abstract Aerodynamic sound is one of the causes of noise in high-speed trains, automobiles, and wind turbines. To investigate the characteristics of aerodynamic sound generation, measurements around the sound sources are required. Aerodynamic sound is typically measured using microphones. However, microphones cannot capture the near-field of aerodynamic sound because they become new noise sources inside the air flow. To observe the aerodynamic sound near-field, we performed two-dimensional visualization of aerodynamic sound using an optical method. The optical method used in this research, parallel phase-shifting interferometry (PPSI), can detect the pressure within the measurement area as variations of the phase of light. PPSI can therefore visualize the pressure fields. We visualized both the sound pressure and flow components of the sound generated by flow around a square cylinder and flat plates. The visualized pressure fields are provided as animations in the online resources. Analysis of the sound and flow component time variations confirmed the correlations between them. Graphic abstract
Wollaston prism Aperture Lens Quarter wave plate High-speed polarization camera
Visualized sound generated by flow around a square cylinder
5 0
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0
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0.04 t = 0.05 [s]
0.05 0.06 Time [s] t = 0.06 [s]
0.07 t = 0.07 [s]
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t = 0.08 [s]
40 mm
Square cylinder
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Amplitude [Pa]
10 mm Nozzle
100 mm
Microphone
Flat plates
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Supporting rod
10 mm
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t = 0.04 [s]
Nozzle
100 mm
0.01 t = 0.03 [s]
Microphone
Phase of light [rad]
Lens
Laser
Beam splitter
Visualized sound generated by flow around flat plates
5 0 -5 0
0.01 t = 0.03 [s]
0.02 t = 0.04 [s]
0.03
0.04 t = 0.05 [s]
0.05 0.06 Time [s] t = 0.06 [s]
0.07 t = 0.07 [s]
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0.09 t = 0.08 [s]
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Acrylic 50 mm board
Phase of light [rad]
Test section Reference light Object light
Lens
Amplitude [Pa]
Optical flat Optical flat
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1 Introduction Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00348-020-03038-x) contains supplementary material, which is available to authorized users. * Risako Tanigawa [email protected] Extended author information available on the last page of the article
Aerodynamic sound is one of the causes of noise in highspeed trains, automobiles, and wind turbines. To reduce such undesired noise, it is important to understand the generation process of the aerodynamic sound. Microphones and microphone arrays are commonly used for measuring radiated aerodynamic sounds. However, they cannot capture sounds inside air flows because microphones installed
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Experiments in Fluids
inside the air flow become new noise sources. Windscreens
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