Newsletter  2021.11  Index

Theme : "Mechanical Engineering Congress, 2021 Japan (MECJ-21)” Preface Masaaki MOTOZAWA, Hideo MORI Turbulence of viscoelastic fluid-from practical examples to turbulent coherent structure Yasuo KAWAGUCHI (Tokyo University of Science) Integration method of measurement and simulation in flow analysis and its applications Toshiyuki HAYASE (Tohoku University) Workshop on Experimental Fluid Dynamics (EFD) Chair: Shouichiro IIO (Shinshu University), Masaki FUCHIWAKI(Kyushu Institute of Technology), Ayumu INASAWA(Tokyo Metropolitan University), and Satoshi KIKUCHI (Gifu University) The Aerodynamic Noise not Made Clear With Acoustic Wind-tunnel Yoshiyuki MARUTA (Chuo University) Analysis of the flow-induced noise with the Extended Proper Orthogonal Decomposition Osamu TERASHIMA, Reon NISHIKAWA (Toyama Prefectural University), and Miyu OKUNO (Kanazawa University) Fan Noise Characteristics and Reduction Hidechito HAYASHI (Nagasaki University)

 

The Aerodynamic Noise not Made Clear With Acoustic Wind-tunnel

Yoshiyuki MARUTA Chuo University

Abstract

The low-noise acoustic wind tunnel is usually used for the sake of clarification and reduction of aerodynamic noise. However, some case studies of aerodynamic noise which were difficult to analyze enough by the experiment with only using acoustic wind tunnel are still remained without executing the best noise control. Two examples of aerodynamic noise with an unsteady airflow are introduced and consider reasons why it was difficult to measure and to analyze.

The 1st one is the estimation of measuring section noise generated from the airflow itself in an acoustic wind tunnel. The measuring section has some aerodynamic noise sources as shown in Figure 1. The addition of these noise is similar to the measured noise except on mid frequency region as shown in Figure 2 although each noise sources are simulated by some experiments with open type acoustic wind tunnel. The reason of under estimation on mid frequency region could be considered that aerodynamic sound generated with the interference flow around crossing area between the floor and the collector is not made clear with open type wind-tunnel as such interference flows might be inner flow phenomena.

The 2nd one is self-excited cavity tone with acoustic resonance in the deep cavity. Acoustic wave of the resonance affects on the vortex shedding frequency as shown in Figure 3. However, the detail aerodynamic mechanism could not be clear by experiments with the acoustic wind tunnel.

Including other case studies that were not fully elucidated, the dominant reasons might be that unsteady flow pattern did not make clear with an acoustic wind tunnel and that the test model could not reproduce the target unsteady flow to understand by only simple experiment.

Key words

Acoustic wind-tunnel, Aeroacoustics, Self noise, Self-excited tone, Acoustic resonance, Cavity tone.

Figures

Figure 1　Sound sources that compose the background noise of the measuring section in the acoustic wind tunnel for automobi入

Figure 2　The influence of the constituent sound sources on the background noise in the floor-mounted measuring section.

Figure 3  Frequency control of cavity tone by acoustic excitation