Numerical Simulation of a Turbulent FSI Benchmark Case

Abstract

In an effort to expand the capabilities of a validated simulation environment for fluid-structure interaction to turbulent flows, we present the simulation of a turbulent FSI benchmark case with large displacements in a simplified two-dimensional unsteady RANS setup. We find a fair agreement to experimental data that encourages further refinement of our approach and future three-dimensional simulations with eddy-resolving schemes.While considerable progress has been made in the field of computational fluid-structure interaction during the last decade, little research is put into application to turbulent flow, which, in turn, has a high relevance to real-world applications. To measure the performance of turbulence models in FSI, researchers need a reliable test case database. As one of the first test cases for turbulent FSI, Gomes et al. [1] presented experiments with a swiveling structure in various flow regimes. The aim of this work is to present a numerical solution to this case in order to validate our simulation environment, while adding exprience with this test case for a better assessment. Test case setupThe examined structure is a pivotable circular cylinder, mounted between the side walls of a channel. Attached to its downstream rear is a flexible membrane with an end mass. Please refer to [1] for a detailed description of the geometry and material properties. When exposed to a flow of about Re b = 15 400 (based on the cylinder diameter), the structure responds with a periodical cylinder rotation and a swiveling motion of the membrane sheet, while the fluid forms a vortex street in the cylinder wake. The excitation mechanism of the structural movement is identified by the experimenters as instability-induced, meaning that the frequency of the fluid instability (here: the vortex street) lies close to an eigenfrequency of the isolated structure, and is therefore causing the excitation of the corresponding mode.The software package to solve for this coupled problem with an implicit partitioned approach consists of a fluid solver, a structural solver, and a coupling software, as described in [2]. The baseline computations were conducted using a second-order accurate MUSCL scheme for the discretization of the convective fluxes, and a second-order backward differencing scheme for time advancement. The structural domain is spatially discretized with linear block elements based on an enhaced-strain formulation, while time is advanced with the Hilbert-Hughes-Taylor method of second order.For the actual computations the extension of the domain in the spanwise direction was neglected, resulting in a twodimensional setup. Slip walls replaced the channel walls to save computational resources, accounting for a very low estimated blockage due to channel boundary layers. The domain was extended in both up-and downstream directions to avoid unphysical interference of the spatially constant boundary conditions with the flow field. A transient RANS approach was taken to consider turbulent flow, employing the ζ-f model [3]. ...