Compressible Navier-Stokes analysis of an oscillating wing in a power-extraction regime using efficient low-speed preconditioning

摘要

A wing that is simultaneously heaving and pitching may extract energy from an oncoming air flow, thus acting as a turbine. This paper analyzes the unsteady aerodynamics of such a device by means of time-dependent laminar flow simulations performed with a research compressible finite volume Navier-Stokes solver. The study confirms the findings of another independent report that the efficiency of the power extraction of this device can be of the order of 35%, and such an efficient operating condition is characterized by a strong dynamic stall. This study is part of a wider research programme aimed at developing a general-purpose computational framework for unsteady aerodynamic and aeroacoustic wind energy engineering. In view of aeroacoustic applications, the developed flow solver uses the compressible formulation of the Navier-Stokes equations with carefully optimized low-speed preconditioning. To demonstrate the modeling capabilities, the accuracy and the high computational performance of the developed low-speed preconditioning technology, the unsteady aerodynamics of the energy-extracting device is simulated by using a computationally challenging freestream Mach number of 0.001. A mixed preconditioning strategy that maintains both the nominal accuracy and the computational efficiency of the solver also for time-dependent low-speed problems is presented. The study also assesses the impact of a semi-implicit treatment of the unsteady source term associated with the discretization of the physical time-derivative of the governing equations on the numerical stability of the explicit multigrid integration.