Numerical strategy of modelling flexible vegetation flows using a semi-resolved numerical model by means of distributed virtual body forces

Abstract

Aquatic flexible vegetation is widespread in rivers, lakeshores, harbors, and coastal areas and plays an important role in the riverine and coastal ecosystems. The flow with flexible vegetation is difficult to simulate due to the complex motions of flexible vegetation and fluid. This work proposes and validates a semi-resolved numerical model coupling the computational fluid dynamics (CFD) and flexible rod dynamics (FRD) using a promoted two-way domain expansion method. The governing equations in the FRD model are solved by the finite element method (FEM), and the CFD is implemented by the finite volume method (FVM). The vegetation effect is added by introducing body forces into the Reynolds-averaged Navier-Stokes equations as point source terms. To mimic the flexible vegetation stem with the anisotropic cross-section, a named distributed virtual body forces method (DVBFM) was first proposed to model the fluid-solid body coupling. A test case of flow around a single flexible plate was first designed to strictly validate the numerical scheme. The model was then further validated by experimental results of flow with a gently undulating patch of flexible plates. Finally, the test case of flow through a wavy patch of flexible vegetation, mimicked by the plates, was used as a benchmark to validate the usability of the model for flexible vegetation flow simulation in a practical engineering sense.