Low-Mach preconditioned boundary conditions for compressible solvers

Abstract

Approaching the incompressibility limit in CFD applications where compressible, density based solution methods are employed, is accompanied very often not only by slow convergence of the residuals but also by a strong degradation of the solution quality. This issue is particularly severe in turbo-machinery applications, where large variations of flow regimes occur. Low-Mach preconditioning methods can be applied to the Euler- and Navier-Stokes equations to alleviate such difficulties. As noted by several authors, these techniques can cause stability problems especially in proximity of the domain’s boundaries. In particular, it has been demonstrated that an appropriate scaling treatment is also required for characteristic-based boundary conditions. In the current work we present the theoretical development and application of preconditioned impermeable boundaries in combination with preconditioned far-field conditions in the in-house CFD code TRACE.