Again we look at a plane parallel situation as sketched here where the two colliding flows are momentum balanced. There is no global motion or acceleration. The matter within the cold dense layer then is supersonically trubulent, causing the mean density of the layer to be substantially reduced. At early times of the evolution a Vishniac-type of instability can be observed under isothermal conditions. However, additional non-linear effects dominate the scenario soon.
Unstable behaviour is also characteristic for radiative colliding flows in massive binary systems .
As can be taken from the schematic setting the situation now is no longer plan parallel. 2D simulations assuming axial symmetry reveal that the interaction zone between the winds of the two massive stars forms no smooth cone at all. It is tilted and twisted instead, containing high density knots and causing large voids through shielding effects. The code is second order in space and time. Strang splitting is used to treat source terms.