Stereoscopic particle image velocimetry measurements are made in two wall-parallel planes-one within and the other at the outer edge of the roughness sublayer-for flow over a rough-wall topology replicated from a turbine blade damaged by deposition of foreign materials. The surface roughness studied herein is highly irregular, contains a broad range of topological scales and is therefore representative of what one might encounter in a variety of technologically-relevant flows of interest. Significant modification of the turbulence within the roughness sublayer (y = 0.0655 = 1.7k, where k is the characteristic roughness height) is observed at streamwise-spanwise locations that are coincident with dominant topological features, particularly strong enhancement of the wall-normal velocity fluctuations, the Reynolds shear stress and the swirling strength (a vortex identifier). These heterogeneities are found to diminish significantly toward the outer edge of the roughness sublayer (y = 0 155), with the statistics of the turbulence relaxing toward a relatively homogeneous state in both the streamwise and spanwise directions. Interestingly, the heterogeneities observed within the roughness sublayer are quite localized around dominant topological features, indicating that sustained wakes are not generated downstream of these roughness features.
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