Sensitivity of turbulence in transpired channel to injection velocity small-scale nonuniformity

Turbulence in a channel flow with a fully transpired wall has been investigated experimentally. Two-dimensional particle image velocimetry is used to measure the instantaneous flowfields within the channel for two different porous surfaces: a 6.35-mm honeycomb and a 3.175-mm honeycomb. The 6.35-mm honeycomb creates a larger fluctuation of the injection velocity than the 3.175-mm honeycomb by a factor of 1.7. The boundary conditions on the porous surface are very important to the internal core flow evolution and flow pattern. For a coarse porous surface (the 6.35-mm honeycomb with higher perturbation level on the transpiration surface), 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 (the 3.175-mm honeycomb, with relatively lower perturbation level on the surface), the mean velocity profiles are very close to the analytical laminar solution for a considerable downstream length, and the turbulent shear stress is much smaller than in the first case. Therefore, profound modification of the flow structure can occur due to the effect of nonideal wall boundary conditions on the porous surface.