Turbulent Navier-Stokes analysis of an oscillating wing in a power-extraction regime using the shear stress transport turbulence model

A wing that is simultaneously heaving and pitching may extract energy from an oncoming air or water stream. The aerodynamic performance of this device in terms of extracted power and energy conversion efficiency is here investigated by means of time-dependent turbulent flow simulations performed with a compressible Reynolds-averaged Navier-Stokes research solver using the K − ω shear stress transport model of Menter for the turbulence closure. Previous studies of this device have focused primarily on laminar flow regimes, and only recently systematic turbulent flow analyses of this device have appeared. This paper presents comparative computational fluid dynamics analyses of the energy extraction process in a fully turbulent and a fully laminar flow regime. Presented results highlight that (a) substantial differences of the flow aerodynamics exist between the two cases, (b) the efficiency of the device in the considered turbulent and laminar regimes achieves values of about 40% and 34% respectively, in line with the findings of previous independent studies, and (c) further improvement of the efficiency observed in the turbulent regime may be achieved by optimizing the kinematic characteristics of the device including turbulent Reynolds number effects in the flow analyses used for the optimization. On the algorithmic and modeling sides, the analyses make use of a computationally efficient method for the fully coupled semi-implicit integration of the time-dependent Navier-Stokes equations and the two equations of the K − ω shear stress transport model. The paper also provides a systematic assessment of the impact of the turbulent wall boundary condition for the specific dissipation rate on the computed flow field. It is highlighted that the solution variations due to particular choices of this boundary condition may be higher than those caused by the use of different turbulence models.