Experiments on the two-dimensional flow of a grain–water mixture past a circular cylinder

We present experiments with a mixture of grains and water around a circular cylinder. Flow is driven by the internal cylinder of a Taylor–Couette cell. Velocity measurements of the mixture at the external surface are carried out using a commercial particle image velocimeter. The flow regime is in the macroviscous range and the flow field is similar to that generated by a Newtonian fluid around a circular cylinder, with a wake and a recirculation zone. Like in other granular flows, the velocity covariance tensor and the rate of deformation tensor are not collinear; they have principal axes rotated nearly 45°. Near the body, the velocity scale of the wake decays linearly at high Reynolds numbers and logarithmically at low Reynolds numbers. The transverse length scale increases as x′n (x′ measured along the axis of symmetry with the origin at the boundary of the body) with n < 0.5 (or nearly zero in some flow conditions).