r-ϕ plot of the radial velocity a) and the azimuthal velocity b) at t = 173 orbits. Both quantities are given in units of u_K(R_∗). The dashed white lines in both plots trace the contour of u_ϕ = 0.15 and 0.6 (from left to right). The direction of the unperturbed flow is from bottom to top. The images have been taken at a high activity state and the strong shocks in u_r and the heavy deformation of the interface (see b)) are clearly visible.