Flow around permeable porous plates placed normal to a horizontal wall

Abstract

The flow around a two-dimensional permeable porous plate placed normal to a horizontal flat wall was investigated with the aid of a laser Doppler velocimetry (LDV). The experiment was performed in a circuit-type wind tunnel having a test section of 200 mm in width and 200 mm in height. Three kinds of porous metal plate of different porosity and permeability were considered in the present work. Mean velocity vector fields in a streamwise wall-normal plane indicated that a recirculation region behind the porous plate moved to downstream with increasing in porosity. At the highest porosity,the recirculation region disappeared and a forward (streamwise) flow occupied in the whole region downstream of the porous plate due to the air flow permeation. These velocity profiles were compared to the theoretical analysis from Görtler, and it was found that the present results agreed with theoretical ones in the region where the forward flow dominated. A streamwise component of root-mean-square velocity fluctuation was enhanced just behind the porous plate with highest porosity. However, at farther downstream, it was weaker than that observed downstream of impermeable plate. Furthermore, a wall-normal fluctuating velocity decreased over the porous plate, although it rapidly increased immediately above the impermeable plate. To estimate a drag force acting on the porous plate, a simple technique based on a momentum balance of the flow was applied. The net body force was determined from the conservative form of the momentum equations by using the measurements of the velocity and pressure profiles. The results of the analysis showed a decrease in the drag force increasing permeability of the porous plate. The behavior of velocity field suggested that the permeable porous plate led to stable windbreak effect.