Experimental study of the grain-water mixture flow past a cylinder of different shapes.

This paper reports on the experiments of the flows of a mixture of grains and water around a circular or triangular cylinder, where the two-dimensional flow is driven by the internal cylinder of a Taylor-Couette cell. The working conditions during tests are such that instabilities do not appear. Velocity measurements of the mixture at the external surface are carried out using the PIV technique. The flow field is very different from that of a Newtonian fluid. However, the streamline patterns look similar, if the flow directions are ignored, as it happens for a dry granular stream. A limited recirculation zone behind the triangular cylinder is present, whose size is much less than that for a Newtonian fluid and is absent for dry granular stream. Upstream of the triangular cylinder, a zone of sediments almost at rest is present, with a semi-circular shape and an extension independent on the Reynolds number. It seems that the flow is controlled by factors downstream the location of interest. Vorticity scales with both the size of the obstacle and the free stream velocity, and is confined near the vertices at the base of the triangular cylinder. Compared to the vorticity field for the Newtonian fluid case, it spreads more upstream. The normalized energy of vortices has a probability distribution function with a peak and a steep reduction, but does not scale with the Reynolds number. The contribution of clockwise and counter-clockwise vortices is roughly balanced.