Large-eddy simulation-based fluid–structure interaction framework for predicting coupled aero-vibro-acoustic instabilities in turbopumps

The design and operation of rocket engines are challenging due to the intricate dynamics and complexity of the interactions between components. One such critical component is the turbopump, a turbomachinery device responsible for delivering the propellants to the combustion chamber at an optimized pressure. During operations, the turbopump is prone to the “pressure band” vibration problem, a self-sustained oscillatory motion of the fluid capable of coupling with adjoining components. It poses an enormous risk to the structural integrity of the device. The compressible fluid–structure interaction exposes a three-way aero-vibro-acoustic coupling between the fluid, the structure, and the turbopump cavity acoustic modes. High-fidelity numerical simulations equipped with recent experimental and theoretical efforts hold significant potential to advance the state of the art in predicting and understanding this phenomenon. To address this problem, we propose a large eddy simulation (LES)-based fluid–structure interaction (FSI) framework using the partitioned coupling scheme that combines an existing LES compressible flow solver and a modal analysis and elastodynamics solver for the structure. The solvers within the framework target turbomachinery applications where the density ratio between the solid and fluid is typically quite large. The validation of the structural solver and the coupled FSI solver is first carried out using two dimensional (2D) and three dimensional (3D) test cases from the literature. Then, the proposed FSI framework is used to simulate the instabilities occurring due to the interactions between the flow, the disk, and the cavity of a 3D experimental reduced-scale turbopump. The simulation results show excellent agreement with the experiments, demonstrating the capability of the FSI framework in capturing such complex aero-vibro-acoustic interactions and instabilities.