Fluid–structure interaction-induced oscillation of flexible structures in laminar and turbulent flows

Abstract

Self-excitation of the motion of a structure has become a prominent aspect of engineering projects over recent years as designers are using materials at their limits, causing structures to become progressively lighter, more flexible and, therefore, prone to vibrate. Stimulated by the increasing interest in fluid-structure interaction (FSI) problems, this study investigated the instability and consequent FSI-induced self-excited oscillation of flexible structures in uniform flows at Reynolds numbers between 10 and 1.69 × 10 5 . The investigations were performed in both water and a highly viscous syrup (ν = 1.64 × 10 −4 m 2 s −1 ) and considered three structures of different geometries. The results were conclusive in showing that the motion of the structure was characterized by a sequence of oscillation modes as a function of the characteristics of the structure and flow properties. In addition, it was possible to identify the self-excitation mechanisms as being of the instability-induced excitation (IIE) or movement-induced excitation (MIE) types. IIE was observed to be the most dominant mechanism of excitation at lower velocities and it was defined by a direct relation between the flow fluctuation and natural frequencies of the structure. For that reason, IIE was strongly determined by the geometry of the front body of the structure. At higher velocities, the amplitudes of the flow disturbances generated by the structure movement increased and excitations of the MIE type became predominant for all structures. The MIE mechanism was found to be weakly influenced by the shape of the structure but very sensitive to its dynamic characteristics and to the properties of the fluid, especially the Reynolds number.

Validation of a non‐conforming monolithic fluid‐structure interaction method using phase‐contrast MRI

“…Verification and validation are important to confirm fidelity and assess the capabilities of established and newly proposed mathematical models and numerical algorithms. Thus, standard numerical benchmark problems [22][23][24][25][26] and FSI experiments [27][28][29][30][31][32][33][34][35] have been developed over the last decades and found widespread use. In this tradition, a recently developed 3D FSI experiment 36,37 introduces two new challenging benchmark test cases that involve steady and periodic interaction between a moderately viscous incompressible fluid and an incompressible nonlinear solid in a 3D setting.…”

Flow past a cylinder with a flexible splitter plate: A complementary experimental–numerical investigation and a new FSI test case (FSI-PfS-1a)

“…The laminar benchmarks proposed above are all purely numerical, i.e., a cross-comparison between different numerical results is possible, but no rigorous validation against experimental measurements can be carried out. In order to close this gap, a nominally 2D laminar experimental case was provided by Gomes andLienhart (2006, 2013) and Gomes (2011): A very thin metal sheet with an additional weight at the end is attached behind a rotating circular cylinder and mounted inside a channel filled with a mixture of polyglycol and water to reach a low Reynolds number in the laminar regime. Experimental data are provided for several inflow velocities and two different swiveling motions could be identified depending on the inflow velocity.…”

“…This study also presents the first comparison between experimental data and predicted results achieved by the present code for a turbulent FSI problem. As another turbulent experimental benchmark, the investigations of Gomes andLienhart (2010, 2013) and Gomes (2011) have to be cited: the same geometry as in Gomes and Lienhart (2006) was used, but this time with water as the working fluid leading to much higher Reynolds numbers within the turbulent regime. The resulting FSI test case was found to be very challenging from the numerical point of view.…”

Numerical FSI investigation based on LES: Flow past a cylinder with a flexible splitter plate involving large deformations (FSI-PfS-2a)

“…Therefore, these publications cannot be used to completely validate FSI codes. More recently, Gomes and Lienhart [11,12,13] have published several FSI test cases including detailed experimental data based on the following geometry: A very thin metal sheet with an additional weight at the end is attached behind a rotating circular cylinder and mounted inside a water channel. The resulting FSI test case was found to be very challenging from the numerical point of view (combination of two-dimensional elements for the thin structure and three-dimensional elements for the rear weight, rotational degree of freedom of the cylinder).…”

“…For this purpose the geometry used in the previous test case (FSI-PfS-1a) is slightly modified: A 2 mm thick flexible plate is clamped behind a fixed cylinder. However, this time a rear mass is added at the extremity of the flexible structure, but in contrast to the setup of Gomes and Lienhart [11,12] the rear mass possesses the same thickness as the rubber plate avoiding a jump in the cross-section. Moreover, the material (para-rubber) is less stiff than in FSI-PfS-1a.…”