Steady and unsteady multiblock hovering rotor simulations

Abstract

A multiblock upwind Euler solver is presented and applied to multibladed lifting hovering rotor flow. Hovering rotor flows can be simulated as a steady case in a blade-fixed rotating coordinate system. Furthermore, periodic boundary conditions mean that only part of the domain need be considered, and so a single-block structured grid can be used. However, forward flight simulation will always require an unsteady solution, and the complete rotor disc must be considered, so a multiblock grid is preferable, for a structured grid solution, particularly to represent complex blades or hubs. Hence, as a stepping stone in the development of a forward flight simulation tool, both explicit steady and implicit unsteady simulations of the same hovering case are presented using a multiblock grid. Convergence of the two approaches is examined and compared, in terms of residual history, cost and solution evolution, as a means of both validating the unsteady formulation and considering implications for forward flight simulation. Consideration of the solution evolution and wake capturing shows that, for hovering rotor cases, the unsteady and steady solutions are the same, but the unsteady solution is more expensive in terms of CPU time. It is also shown that, for hover, the fewer real time steps taken per revolution, the more efficient the implicit scheme will be.