Three convective flux types exist when using the density-based solver:
Roe-FDS splits the fluxes in a manor that is consistent with their corresponding flux method eigenvalues. It is the default and is recommended for most cases.
AUSM provides exact resolution of contact and shock discontinuities and it is less susceptible to Carbuncle phenomena.
Low diffusion Roe-FDS is used when the LES viscous model is enabled. It reduces the dissipation in LES calculations and is used only for subsonic flows.
The convective fluxes are selected from the Flux Type drop-down list under Solver Parameters in the Solution Controls panel (Figure 25.10.1).
Solve Controls Solution...
Select Roe-FDS, AUSM, or if the LES viscous model is enabled, Low Diffusion Roe-FDS.