The line driven instability is expected to form shocks in hot star winds, with the shocks enclosing shells of highly compressed gas. In numerical simulations, photospheric turbulence leads to fragmentation of the intershell gas into highly accelerated clumps of presumably small lateral length scale. The clumps collide at high speed with the compressed shells. The corresponding X-ray flashes can match observed fluxes.

A rich flow geometry was recently found for line driven winds from accretion disks. At a certain radius in the disk, a rather sharp jump occurs in wind properties. While the wind launched from smaller disk radii is expected to be unstable, simulations show instead a chaotic outer wind.

Finally, radiative-acoustic or Abbott waves are discussed. Along slow, sub-critical wind solutions, these waves propagate inwards at large speed, in the stellar frame. If not properly dealt with in the outer boundary condition and the Courant time step, the waves may cause a numerical instability, which drives the wind to the critical CAK solution. I discuss conditions under which sub-critical solutions are stable, even to large perturbations.