Structure of turbulence in channel flow with a fully transpired wall

Abstract

The structure of turbulence in a channel flow with a fully transpired wall has been investigated experimentally. 2D Particle Image Velocimetry is used to measure the instantaneous flow fields within the channel for three different porous surfaces: 1/4 honeycomb, foam (used as the direct porous interface and attached to a 1/4 honeycomb) and 1/8 honeycomb. Mean flow properties and statistics are obtained by analyzing the instantaneous measurements. Comparison with analytical and computational results is made. It is found that the boundary conditions on the porous surface are very important to the internal core flow evolution and flow pattern. For a coarse porous surface (in this paper, 1/4 honeycomb), the mean flow differs significantly from the classical laminar solution and computational results, and much more turbulent shear stress is indicated. However, with small pore size (in this paper, 1/8 honeycomb), the mean velocity profiles are very close to the laminar solution for a considerable downstream length, even though large turbulence intensity (5%) is observed. Therefore, profound modification of the flow structure can occur due to the effect of non-ideal wall boundary conditions on the porous surface. In addition, the location where the maximum RMS turbulence intensity occurs moves closer to the porous surface with increasing downstream position.