Numerical investigations on unsteady vortical flows and separation-induced transition over a cycloidal rotor at low Reynolds number

Abstract

The unsteady vortical flows and laminar-turbulence transition over a 2-bladed cycloidal rotor are investigated numerically at two advance coefficients, with special emphasis on the influence of two turbulence models, namely the original SST k-ω model and SST γ-Reθt transition model. The numerical results are compared with the existing numerical and experimental data, in terms of the global performance and detailed internal flow structures. The primary results show that increasing the advanced coefficient can’t change the transition location of the performance for the single blade, but the magnitudes of these variables. Then, combined the forces acting on two blades and the blade loadings, the difference of the vertical force and propulsive force of the rotating system and single blade are clarified clearly for two turbulence models. Finally, at advancing side, the transition and its evolution on a single blade is elaborated. It shows that the SST γ-Reθt transition model is superior in predicting the overall performance, and is highly subjected to the disturbances, characterized by the large-scale vortex structures and massive flow separation, compared with SST k-ω model. Simultaneously, it has the capability to capture the transition process, from growing waves of the laminar boundary layer induced by the roll-up vortices to the fully generation of the separation bubble. It believes that this work can deep the understandings of underlying flow physics inside the cycloidal roto at low Reynolds number.