Turbulent flow past a smooth and rigid wall-mounted hemisphere

Semi-confined flows

Underlying Flow Regime 3-33

Abstract

The objective of the present contribution is to provide a detailed experimental and numerical investigation on the turbulent flow past a smooth and rigid wall-mounted hemispherical obstacle. For this purpose, the hemisphere (diameter D) is exposed to a thick turbulent boundary layer of the thickness δ = D/2 at Re = 50,000. In order to reproduce the desired boundary layer in the experiment a combination of specific fences are placed in the upstream region of the wind tunnel. Detailed measurements of the inflow conditions are realized using laser-Doppler and hot-film probes. Furthermore, the experimental data are utilized to generate matching inflow conditions between numerical inlet and the experimental inflow conditions. These clearly defined boundary and operating conditions are the prerequisites for a combined experimental and numerical investigation of the flow field relying on the laser-Doppler anemometry and on a large-eddy simulation.

The numerical results are produced by a finite-volume Navier-Stokes solver for block-structured curvilinear grids. A fine wall-resolved mesh is applied resulting from a preliminary study. A parallel analysis is conducted to select a correct subgrid-scale model.

The final investigation includes a profound analysis on the unsteady flow features observed in the vicinity of the hemisphere like the horseshoe vortex, the recirculation area, the hairpin structure or the vortex shedding processes. A detailed discussion of the time-averaged flow field comprising the mean velocity field as well as the Reynolds stresses is also presented. Both, experimental and numerical, results are found to be in close agreement.