The Interaction of Porous Material Coating With the Near Wake of Bluff Body

Abstract

The flow around a circular cylinder with porous material coating (PMC) is numerically investigated based on unsteady Reynolds-averaged Navier-Stokes (URANS) method at subcritical Reynolds number. The results are compared with some available results in the open literature. The interaction of PMC with the near wake of a circular cylinder such as streamline, vorticity field, and shear stress are studied in detail. Subsequently, the fluctuation forces and velocity distribution in the boundary layer are analyzed and the effect of various thicknesses of PMC is investigated. The numerical results reveal that PMC has prominently modified the flow characteristic of the near wake of circular cylinder and significantly mitigated the fluctuations of aerodynamic forces from two aspects of frequency and amplitude. It means that the vortex shedding from the bluff body is suppressed. It also is found that the thickness of the PMC is a sensitive parameter to the aerodynamic forces and velocity distribution in the boundary layer. Furthermore, the mean drag can be reduced to a certain extent when the thickness is appropriate. It is expected that the modification of flow characteristic and aerodynamic forces is closely related to the flowinduced noise reduction. Those results will be helpful to understand the mechanism of flow control on bluff body flow by using porous material coating and accumulate meaningful information for further industrial application.

Boundary layer flow interaction with a permeable wall

“…The effectiveness of porous treatments as a flow and noise control technique relies greatly on the porosity (ϕ) and permeability (κ) of the material. [33][34][35][36] Given the importance of these two quantities, especially in the context of flow and noise control, both parameters have been measured for the porous samples studied here. The porosity of a porous medium is a measure of the proportion of the total volume of the material occupied by pores.…”

Trailing-edge flow and noise control using porous treatments

“…The results also showed the changes to the velocity slip condition in the case of porous surface and the flow penetration into the porous medium. Liu et al (2014) also investigated the influence of porous coatings on the near-wake structures of a round cylinder and showed that the porous cover can significantly change the flow characteristic of the cylinder nearwake by detaching the recirculation zone, which consequently results in the reduction of aerodynamic forces acting on the cylinder. More recently, Liu et al (2015) studied the flow characteristics within the gap region of two round cylinders using unsteady CFD and demonstrated that the overall noise level can be reduced 15 dB by using porous covers, which is believed to be due to the stabilization of the gap flow and reduction of turbulence impingement on the rear cylinder.…”

Numerical Analysis of Metal-Foam Application for Trailing Edge Noise Reduction

“…Numerical studies on the aeroacoustics applications of porous materials have been reported in the literature. For instance, Liu et al investigated the effect of porous material coating on a cylinder [14] and a tandem cylinder [15] configurations. The porous coating was represented as an equivalent fluid region where the mass and momentum conservation equations were modified to include Brinkman-Forchheimer-Darcy model (sometimes also referred as the Hazen-Dupuit-Darcy model [16]).…”