Spatial structure of a turbulent boundary layer with irregular surface roughness

Particle image velocimetry experiments were performed to study the impact of realistic roughness on the spatial structure of wall turbulence at moderate Reynolds number. This roughness was replicated from an actual turbine blade damaged by deposition of foreign materials and its features are quite d...

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Bibliographic Details
Published in:Journal of fluid mechanics 2010-07, Vol.655, p.380-418
Main Authors: WU, Y., CHRISTENSEN, K. T.
Format: Article
Language:English
Subjects:
Boundary layer
Boundary layer and shear turbulence
Boundary layers
Correlation
Exact sciences and technology
Flow velocity
Fluid dynamics
Fluid flow
Fluid mechanics
Fundamental areas of phenomenology (including applications)
Instrumentation for fluid dynamics
Physics
Reynolds number
Roughness
Shear stress
Surface roughness
Turbines
Turbulence
Turbulent flow
Turbulent flows, convection, and heat transfer
Vortices
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Summary:Particle image velocimetry experiments were performed to study the impact of realistic roughness on the spatial structure of wall turbulence at moderate Reynolds number. This roughness was replicated from an actual turbine blade damaged by deposition of foreign materials and its features are quite distinct from most roughness characterizations previously considered as it is highly irregular and embodies a broad range of topographical scales. The spatial structure of flow over this rough surface near the outer edge of the roughness sublayer is contrasted with that of smooth-wall flow to identify any structural modifications due to roughness. Hairpin vortex packets are observed in the outer layer of the rough-wall flow and are found to contribute heavily to the Reynolds shear stress, consistent with smooth-wall flow. While similar qualitative consistency is observed in comparisons of smooth- and rough-wall two-point correlations, some quantitative differences are also apparent. In particular, a reduction in the streamwise extent of two-point correlations of streamwise velocity is noted which could be indicative of a roughness-induced modification of outer-layer vortex organization. Proper orthogonal decomposition analysis reveals the streamwise coherence of the larger scales to be most sensitive to roughness while the spatial characteristics of the smaller scales appear relatively insensitive to such effects.
ISSN:0022-1120
1469-7645
DOI:10.1017/S0022112010000960