Prediction of aeroacoustic sound using the flow field obtained by time-resolved particle image velocimetry

Abstract

Based on vortex theory, we experimentally and directly predict sound sources distributing in the flow field and determine the sound pressure level as a result of the spatial integration of sound sources. In employing this direct evaluation method for the aeroacoustic sound, the problem is that a large integration area is required to minimize errors caused by the sudden truncation of the integration area; we overcome it by adopting and applying a modified formula that neglects the quadrupole sound under the condition that the dipole sound is dominant at a low Mach number. Through the flow field measurement using a time-resolved particle image velocimetry (TR-PIV) technique, we will clearly demonstrate the feasibility of our method and the distribution of dipole sound sources in the vicinity of a body even if a comparatively small integration area must be taken. In this basic study, a circular cylinder with a diameter of 6.0 mm is used; the spatially integrated sound pressure is compared with the actual sound pressure which is measured with a microphone. Further, the sound sources evaluated using only the flow field are determined, which give us detailed information about the amplitude and phase of the sound source structure. This direct evaluation method for the dipole sound is applicable to a more complex body.

Measurement techniques for aeroacoustics: from aerodynamic comparisons to aeroacoustic assimilations

“…Still, important studies need to be mentioned as attempting to create a direct link from the velocity fluctuations description to the prediction of the aeroacoustic sound from PIV, by leveraging the Navier-Stokes equations and appropriate aeroacoustic analogies. Applications on cylinders of this approach were conducted by Henning et al [171] and Uda et al [172] with a combination of PIV flow-field measurements and microphone recording of the radiated sound. Other works replicating the approach seen with HWA and LDV although for the study of flow structures at different scale ranges can be found in jet noise, for example as seen by Schram et al [173], and later by Rego et al [174] and Cavalieri et al [175] for low speed, and from by Akislar et al [176,177] at high speed.…”

PIV-based pressure measurement

“…PIV was used by Schröder et al (2006) for the investigation of trailing edge noise sources, while jet-noise produced by vortex pairing was investigated by Schramm et al (2004) and Violato et al (2010). Henning et al (2008) and Uda et al (2011) investigated the aeroacoustic noise generation of cylinder wakes by a combination of PIV flow field measurement and microphone recording of the radiated sound. Also Kastner et al (2009) report on the combined use of PIV and a microphone array, to investigate the relation between flow fluctuations and sound generation in a subsonic jet.…”

Aerodynamic Sound Sources from Flows around a Rectangular Cylinder with a Low Mach Number

“…なお, 以下では前述の二重極音および四重極音を, 参考文献 (7), (10)にならい, それぞれ音源から発生した音波が 物体により散乱することで発生する音として散乱音, 物体の散乱なしに観測者に届く音という意味で直接音と呼 ぶ. このような場合, 例えば円柱まわりの流れでは, 円柱から離れた音源から発生した音波に比べ円柱近傍の音 源から発生した音波がより効率良く遠方へ散乱され, 円柱近傍の音源が主要な音源となる (9) . しかしながら, 渦か らの音の発生機構を明らかにする際には, こうした散乱効果を除去することで, より厳密な議論が可能となると 考えられるが, こうした議論はこれまで十分になされていない.…”