Numerical analysis of transport in porous media to reduce aerodynamic noise past a circular cylinder by application of p
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Numerical analysis of transport in porous media to reduce aerodynamic noise past a circular cylinder by application of porous foam Yuan Yuan1 • Kuo Xu1 • Ke Zhao1 Received: 8 June 2019 / Accepted: 19 July 2019 Akade´miai Kiado´, Budapest, Hungary 2019
Abstract Metal foams as porous media have very high porosity and good strength. These materials could easily be applied to exterior surfaces of metals used in different industries. Porous media have been used less in the external flows to control the wake region or reduce the generated sound in high-speed flows. In this study, a numerical investigation is done to explore the effect of different characteristics of a porous medium—such as PPI and porosity or porous coating thickness—on the sound generated by a porous-coated cylinder. The governing transport equations in the clear and porous regions are solved using 3D Navier–Stokes and non-Darcy equations, respectively, and employing the large eddy simulation turbulence model. The generated noise is estimated using the Ffowcs-Williams and Hawkings model at the observer location. The results show that use of porous media could considerably reduce the aerodynamic noise provided that its characteristics are selected precisely. For example, results show that a porous-coated cylinder with PPI = 40 has about 30 dB higher overall sound pressure level (OASPL) than one with PPI = 10 with the same porosity and thickness. Same conditions are also observed about the thickness of the coating. The results indicate that an optimal thickness exists for which the OASPL is minimal. For example, porous-coated cylinders with coating thickness of 5 and 15 mm have about 25 dB higher OASPL compared to a cylinder with the coating thickness of 10 mm. Keywords Numerical simulation Transport in porous media Aeroacoustic simulation Ffowcs-Williams and Hawkings model Large eddy simulation
Introduction Nowadays, the flow-induced noise which also known as aerodynamic noise is an important problem for engineers working on the design of apparatus such as aircraft or highspeed trains and cars. The aerodynamic noise is one of the primary sources of sound in modern airplanes. By the advent of the new generation of turbofan motors and utilization of high bypass ducts and serrated nozzles, the noise of motors becomes minimal during the landing. Consequently, the major part of the propagated sound becomes due to aerodynamic noise [1, 2]. However, the main reason
& Yuan Yuan [email protected] 1
School of Mechanical and Precision Instrument Engineering, Xi’an University of Technology, Xi’an 710048, China
of aerodynamic noise is the flow separation occurring behind blunt bodies utilized in some external structures of high-speed vehicles such as the landing gear of an airplane. Ideally, the shape of streamlines in the front and rear of a blunt body is the same in potential or low Reynolds flows. On the other hand, in high-speed flows of a real fluid behind blunt bodies, streamlines distort and wakes
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