Abstract
The flow around a surface mounted cube with incoming turbulent or laminar boundary layer has been topic of many experimental and numerical investigations in the past decades. Despite its simple geometry the flow generates a set of complex vortical structures in front and around the cube, includes flow separation at the three front plane edges with corresponding subsequent shear layer dynamics enveloping recirculation zones. Downstream of the cube a large unsteady flow separation region is present which is associated with typical quasi-periodic bluff-body wake dynamics. Therefore the flow configuration is well suited to enhance the understanding of similar unsteady and separated flow phenomena in many aerodynamic and engineering applications. In the present experimental investigation we aim at resolving a large spectrum of spatial and temporal scales in the flow around a cube with incoming laminar and turbulent boundary layers by using the most recent developments of dense 3D Lagrangian particle tracking (LPT) and high resolution TR-PIV for Reynolds numbers based on cube size in the range text {Re}_H = U_infty ,H,nu ^{-1} = 2000 - 8000. The results documented in the present paper consist of snapshots and the analysis of long time-series of highly resolved 3D and 2D velocity fields suited to enhance the understanding of coherent structure dynamics and of corresponding statistical Lagrangian and Eulerian flow properties. Premultiplied velocity spectra and 3D pressure distributions are calculated and discussed as well. Finally, the measurement data is compared to results obtained with a simulation based on the lattice Boltzmann method (LBM).Graphic abstract
Highlights
In the last few decades, there has been extensive research on turbulent boundary layer (TBL) and turbulent channel flows around wall-attached obstacles, including cubes with various aspect ratios roughly in the range of ∕H ≈ 0.25–5 or H∕h ≈ 0.1–0.3
In order to normalize the time-averaged velocity profiles, estimates of the wall shear stress estimates were obtained through fits to DNS data or using theoretical solution (e.g., Blasius profile for the laminar cases)
Compared to the best-fit to the DNS data performed in the range 10+ < y < 200+, the wall-shear rate estimate from single pixel-line processing is underestimated by about 5% which can be attributed to a bias of the estimated near wall velocity toward zero
Summary
In the last few decades, there has been extensive research on turbulent boundary layer (TBL) and turbulent channel flows around wall-attached obstacles, including cubes with various aspect ratios roughly in the range of ∕H ≈ 0.25–5 or H∕h ≈ 0.1–0.3. Extensive experimental studies have been performed by Castro and Robins (1977), Martinuzzi and Tropea (1993) and Meinders et al (1999) primarily focusing on unsteady pressure distributions gained by probe measurements and wall-shear stress visualizations using oil-film techniques or similar. These studies gained many basic insights into the mean 3D flow structures around and in the wake of the cube using assumptions governed by topological concepts. Near-surface PIV results of the flat plate around and at the walls of the cube itself by Depardon et al (2005, (2006) have allowed the estimation of the related skin friction vector fields along with the identification of locations of mean separation lines, foci- and saddle-point topologies (Depardon et al 2007), which previously was restricted to qualitative visualizations only
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