Comparison of rans and potential flow theory based simulations of a cyclorotor type wave energy converter in regular waves

This paper presents a comparison of results obtained from potential flow theory and field method based simulations of a cyclorotor-type wave energy converter. The simulations are conducted to assess the applicability of several simplifications introduced by the potential flow theory in modelling these devices. All simulations are conducted in a 2D-frame to eliminate the influence of 3D effects such as edge vortices. In the first part of the study, both methods are applied to model a single-foil rotor rotating in still water. The resulting wave elevation patterns are compared to experimental reference data. Differences are discussed and potential sources of these differences elaborated. In the second part of the study, both methods are applied to simulate a device operating in regular waves. Differences in the obtained radial and tangential forces experienced by the foils are discussed and compared with regard to the influence of the wave on foilfoil and foil-free surface interaction. The results obtained in the second part of the study show a considerable deviation between the two methods, mostly when effects such as flow separation and formation of vortices occur. These effects emerge when the rotor rotation rates differ from the wave frequency. While fluctuations of forces due to free surface interaction are observed even when operating at wave frequency, these seem to be mostly captured by the potential flow model. Since hydrodynamics of lift-based wave energy converters are found to be very sensitive to small changes in predicted inflow angles, further experimental data is needed for a qualitative assessment of numerical code performance.

Subjects

CFD

Lift-based

Potential Flow

RANS

Wave energy

WEC

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Comparison of rans and potential flow theory based simulations of a cyclorotor type wave energy converter in regular waves