A semi-implicit partition algorithm for fluid–structure coupling problems based on modal force prediction-correction

The implicit partition algorithm used to solve fluid–structure coupling problems has high accuracy, but it requires a long computation time. In this paper, a semi-implicit fluid–structure coupling algorithm based on modal force prediction-correction is proposed to improve the computational efficiency. In the pre-processing stage, the fluid domain is assumed to be a pseudo-elastic solid and merged with the solid domain to form a holistic system, and the normalized modal information of the holistic system is calculated and stored. During the sub-step cycle, the modal superposition method is used to obtain the response of the holistic system with the predicted modal force as the load, so that the deformation of the structure and the updating of the fluid mesh can be achieved simultaneously. After solving the Reynolds-averaged Navier-Stokes equations in the fluid domain, the predicted modal force is corrected and a new sub-step cycle is started until the converged result is obtained. In this method, the computation of the fluid equations and the updating of the dynamic mesh are done implicitly, while the deformation of the structure is done explicitly. Two numerical cases, vortex induced oscillation of an elastic beam and fluid–structure interaction of a final stage blade, are used to verify the efficiency and accuracy of the proposed algorithm. The results show that the proposed method achieves the same accuracy as the implicit method while the computational time is reduced. In the case of the vortex-induced oscillation problem, the computational time can be reduced to 18.6%. In the case of the final stage blade vibration, the computational time can be reduced to 53.8%.