Unsteady Low Mach Preconditioning with Application to Rotorcraft Flows

A modified low Mach number preconditioning algorithm for the unsteady Navier-Stokes equations is implemented within a diagonalized-implicit dual-time stepping framework. The method utilizes preconditioning based on the unsteady time scales and a novel blended artificial dissipation model, which are shown to be instrumental in preserving both accuracy and convergence over a wide range of Mach number and physical time scales. For demonstration purposes, the method is applied to a simple convecting inviscid vortex as well as to a complex helicopter rotor-fuselage configuration. The test cases highlight the improved accuracy and convergence characteristics of the proposed method and demonstrate that significant performance gains are obtained over traditional methods.