
As discussed in Section 25.4.2, four density interpolation schemes are available when the pressurebased solver is used to solve a singlephase compressible flow.
The firstorder upwind scheme (the default) provides stability for the discretization of the pressurecorrection equation, and gives good results for most classes of flows. If you are calculating a compressible flow with shocks, the firstorder upwind scheme may tend to smooth the shocks; you should use the secondorderupwind or QUICK scheme for such flows. For compressible flows with shocks, using the QUICK scheme for all variables, including density, is highly recommended for quadrilateral, hexahedral, or hybrid meshes. The thirdorder MUSCL scheme is applicable to arbitrary meshes and has the potential to improve spatial accuracy for all types of meshes by reducing numerical diffusion.

In the case of multiphase flows, the selected density scheme is applied to the compressible phase and arithmetic averaging is used for incompressible phases.
