Experimental Investigation of the Influence of Anisotropic Surface Structures on the Boundary Layer Flow

摘要

Blade surface roughness influences the flow behavior and with it the performance of gas turbines and aircraft engines. The relationship between the flow behavior and the surface roughness structures is complex. To characterize the spatial influence of anisotropic roughness distributions on the near wall flow, velocity field measurements are conducted in the central vertical stream-wise plane above generic roughness structures in a water channel by means of stereoscopic particle image velocimetry. A set of anisotropic and isotropic roughness distributions were designed for the experiments. The mean lateral velocity component is analyzed as a function of the spatial parameters which describe the roughness distributions. A new local spacing parameter is introduced to more accurately predict the local influence of the roughness complementing the existing surface roughness characterization parameters that provide a more global classification. The local spacing parameter is calculated by comparing the local lateral distance to the nearest neighboring roughness elements on the left and on the right with respect to the free stream direction. A large spacing parameter indicates a significant lateral spacing inequality and corresponds to a deflection of the flow in the direction of less resistance located in between ridges in the surface roughness geometry.