The simulation of deformation and vibration characteristics of a flexible hydrofoil based on static and transient FSI

摘要

Flexible hydrofoils can be regarded as the simplified lifting bodies of composite propellers, and these hydrofoils are suitable for use in the study of the fluid-structure interaction (FSI) computational method. The hydrodynamic simulation of a rigid cantilevered rectangular hydrofoil is performed first, then the boundary rotational motion and remeshing approach are used for the numerical calculation of the hydrofoil's pitching hydrodynamic performance, and finally the tunnel boundary effect is perfectly simulated via the steps of structured meshing, rotational parameter transforming, and remeshing. The mesh number, boundary layer, orthogonality angle, and turbulent intensity parameters are obtained through comparisons of various models; thus, the Laminar Separation Bubble (LSB) and turbulent transition are captured. Then the static FSI simulation of the flexible hydrofoil is conducted, showing that the lift of the flexible hydrofoil is low and the drag is high for the two-way FSI compared to the one-way FSI. The center of pressure, the maximum deformation, and the stress move toward the leading edge, showing the necessity of the two-way FSI calculation. The transient FSI simulation of the flexible hydrofoil is then studied using the Large Eddy Simulation (LES) turbulence model to calculate the pressure load, which can simulate the turbulence fluctuation as the exciting source of the structural frequency domain load. The calculated first peak frequencies are 96 Hz and 78 Hz at 4 degrees and 8 degrees, respectively. The modal vibration shapes of the POM hydrofoil are calculated showing the first mode of bending, the second mode of twisting and the higher mode of bend-twist coupling. The calculated wet natural frequencies of the POM hydrofoil and the steel hydrofoil show good agreements with experimental values. As the modal rank increases, the POM hydrofoil's wet modal frequency decrease varies from 53.8% to 29.2%, whereas the steel hydrofoil's wet modal frequency decrease varies from 36.9% to 14.2%.