STAR-CCM+ is able to make use of two flow regimes: coupled flow and segregated flow. CD-adapco recommends the coupled flow model for compressible flows, which includes the optional AUSM+ invisic flux scheme.
The coupled flow model solves the conservation equations for mass and momentum simultaneously using a time-marching approach. It can use either the implicit or explicit pseudo-time integration.
The segregated flow model can be used for mildly compressible flow, which is a faster approximation for the solution. This model solves the flow equations individually.