The paper presents computational results of 3D flow past a cylinder forced to oscillate: (a) transversely with respect to a uniform stream and (b) both transversely and in-line with respect to a uniform stream, following a figure-eight trajectory. For a flow from left to right the figure-eight is traversed counterclockwise in the upper half-plane. Direct numerical simulation (DNS) of the Navier–Stokes equations for 3D flow is performed using a spectral element code. Computations are carried out for a Reynolds number equal to 400, at a transverse oscillation frequency equal to the natural frequency of the Kármán vortex street. For both oscillation modes, the transverse oscillation amplitude is varied from 0 to 0.60 cylinder diameters. The forces on the cylinder are calculated and related to flow structure in the wake. The results indicate that, in general, the presence of in-line oscillation increases the magnitude of forces acting on the cylinder, as well as the power transfer from the flow to the structure. Flow visualizations indicate that, for the figure-eight mode, low-amplitude forcing tends to reduce the wake three-dimensionality. However, at high oscillation amplitudes, the wake structure is found to become more complex at increasing amplitude.
Experimental and numerical analysis of the performance and wake of a scale–model horizontal axis marine hydrokinetic turbine
