The flow around a riser can be modeled as the flow around a cylinder, which is an extensively studied problem within the field of fluid mechanics.

In our previous work, VIScous Vorticity Equation (VISVE) method has been proposed and implemented by Tian [1], in order to model the effects of the Leading Edge Vortex (LEV) on propeller performance. The VISVE method is designed to be both spatially compact and numerically efficient in comparison to the commonly used RANS-based models. The method was recently extended in the case of cylinder subjected to uniform inflow [2].

In this study, the VISVE method is applied to alternating flow around a cylinder. The gridding scheme is changed to allow vortices to travel farther on both sides of the cylinder. In addition, the utilized grid is orthogonal and that improves the quality of the results. The vorticity, pressure, and force calculation is improved and the predicted values are compared to those from a commercial CFD software (ANSYS Fluent) in the case of unidirectional as well as alternating flow. It is found that the results from VISVE agree very well with those from Fluent at earlier time steps in the simulation in the case of unidirectional flow, while they were qualitatively similar at later time steps. In the case of alternating flow, VISVE can predict results which are very close to those from Fluent with small Keulegan-Carpenter numbers, while they will deviate at higher KC numbers.

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