Measurement of Aerodynamic Sound Source around a Circular Cylinder by Particle Image Velocimetry

Abstract

The purpose of this paper is to propose a sound localization method as an alternative of the time-resolved particle image velocimetry (PIV) system for detecting the aerodynamic sound source of a circular cylinder in a uniform flow. The sound source intensity of a circular cylinder in a uniform flow is evaluated by measuring the time-derivative of instantaneous velocity field in the flow field using a pair of planar PIV system. It allows the visualization of the sound source intensity distribution, which is the time-derivative of the vector product of vorticity and velocity. The experimental results indicate that the aerodynamic sound is generated from the separation point and the velocity fluctuation in the separating shear layer from the circular cylinder. These results agree qualitatively with the previous findings from experiment and numerical simulation, which supports the validity of the present experimental method for evaluating the sound source intensity distribution.

Sound source and pseudo-sound in the near field of a circular cylinder in subsonic conditions

“…According to the vorticity contours, as the vortices are shed alternately into the wake, the angle of the separated shear layer with the horizontal cylinder tangent line varies with time and the separated shear layer interacts with the cylinder surface alternately. The time-dependent variation of dilatation around the flow separation point suggests that the pressure fluctuation around the flow separation point is the sound source previously detected by Oguma et al (2013) and Oguma, Yamagata & Fujisawa (2014).…”

Sound Source Measurement of a Semi-Circular Cylinder in a Uniform Flow by Particle Image Velocimetry

“…The experiment was performed in an acoustic open-jet wind tunnel, which has been described in Ref. [21].…”

“…Although these experimental methods allow the localization of the aerodynamic sound sources, the last two methods can simultaneously evaluate the sound source and velocity field, which is useful for understanding the generation mechanism of aerodynamic sound. Recently, a method using two sets of standard PIV systems has been reported for the localization of the sound source from a circular cylinder in a uniform flow [21]. This method allows the evaluation of the sound source without relying on the high-speed PIV system; thus, it is well suited for the detection of the sound source from a bluff body of complex geometry for industrial applications, though the applications have not yet been reported.…”

“…Note that the mean freestream velocity in the test section was uniform within an accuracy of ±1%, and the freestream turbulence level was about 1%.The time-derivative measurement of the Lamb vector in Equation (2) is performed using two sets of standard PIV systems, which are illustrated inFigure 1. Each PIV system consists of Nd:YAG lasers (50 mJ/pulse with 15 pulses/sec), two CCD cameras (1280 × 1024 pixels with 12 bits), and a pulse generator, as described in Ref [21]…”

Experimental and numerical studies on Aeolian tone from D-shaped cylinder

“…[16][17][18] The sound source in the flow field was measured experimentally using a combination of microphone measurements and a PIV technique, [19][20][21] and by taking the time-derivative of the velocity field obtained from the PIV. 22 So far, many efforts have been dedicated to analyzing flow structures and aerodynamic sound not only for circular cylinders, but also rectangular cylinders. [23][24][25][26] Fewer studies on the flow structures and aeroacoustics of the D-shaped cylinders have been conducted.…”