Author(s): Yannick Marschall; George Constantinescu; Robert M. Boes; David F. Vetsch

Linked Author(s): David Vetsch, George Constantinescu, Robert Boes, Yannick Marschall

Keywords: Drag forces; Computational fluid dynamics; Numerical simulations; Free-surface flow

Abstract: Numerical simulations are a powerful tool to gain deep insight into the hydrodynamic processes which occur around submerged obstacles like boulders. Over the last decades, different simplified approaches were developed to reduce the computational cost of such simulations. In the popular rigid-lid approach, the water surface is treated as a rigid boundary which results in a reduction of the complexity and a decrease of the computational domain. In this study, we conducted eddy resolving simulations around submerged boulder-like ellipsoids to compare the performance of the rigid-lid and the free surface approach with regard to the flow field and drag and lift forces. Simulations have been conducted for three levels of submergence, from slightly emerged to deeply submerged ellipsoids. We observed good agreement of the flow field and flow parameters between both approaches for the deeply submerged test case. However, for a case with slight submergence, an underestimation of the drag coefficient of more than 25% could be observed with the rigid-lid approach. For even lower submergence levels, different flow structures developed leading to a significant underestimation of the drag forces and overestimation of the vertical uplifting forces. While the results of the deeply submerged case confirm the validity and applicability of the rigid-lid approach, special care has to be taken for lower submergence.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p0071-cd

Year: 2023