Analysis of a boundary layer of a granular mixture flowing past a plate at zero incidence

Abstract

The present paper reports experiments on the flow field of a grain–water mixture around a flat, thin plate at zero incidence. The velocity measurements are performed using a Particle Image Velocimetry (PIV) technique. The Proper Orthogonal Decomposition (POD) analysis reveals that the degree of organisation of the flow field increases with the Reynolds number. The displacement thickness of the boundary layers generally increases downstream and increases slightly with the Reynolds number, which is based on the length of the plate. The vorticity normal to the plane of the flow has a maximum value at the leading edge and is almost invariant with respect to the Reynolds number; additionally, the non-dimensional profiles in the direction normal to the plate show self-similarity in the streamwise direction for a single test, and the profiles are almost coincident for all tests. The flow divergence is assumed to be an indicator of the variation of the sediment volume concentration; it indicates an increment of the sediment volume concentration near the walls of the plate and a spatial periodicity downstream that is triggered for relatively large Reynolds numbers. The spatial correlation analysis allows the evaluation of the integral length scales that are successively utilised in modelling the non-local rheology of the mixture. The velocity profiles have been modelled based on Savage’s model and Bagnold’s experiments, with further modifications from Ertaş and Halsey (2002) that are represented by pseudo-turbulence modelling of the flow field. Vortices have been detected according to the λ2-criterion given by Jeong and Hussain (1995). The statistics of the vortices indicate that no preferential size is selected and that at a high Reynolds number, the most energetic vortices develop near the leading edge.