Time-Refinement Within a Cartesian Off-Body Grid/Curvilinear Near-Body Grid Approach

The reduction of the computational cost of unsteady CFD simulations, especially those involving helicopter rotor flows, is a major concern. The purpose of this paper deals with the development and analysis of the performance of a time-refinement method within a set of Cartesian off-body grids that are automatically generated and adapted. The stability of the numerical scheme, but also the control of the numerical error, using the time-refinement method are assessed here. This technique is validated on the unsteady simulation of the inviscid flow over an in-plane oscillating NACA0012 airfoil. In this test-case, comparisons with a reference computation show no discrepancies due to the timerefinement method, while a significant reduction of the computational cost is obtained. This method is then applied to the inviscid flow simulation over a BO105 rotor in forward flight, assessing the capability of the time-refinement method within the Cartesian mesh adaptation approach to capture vortical wakes more efficiently, without loss of accuracy.