2020 Volume 63 Issue 6 Pages 249-256
Computational fluid dynamics (CFD) analysis coupled with pitching motion of a reentry capsule is performed, and a model equation for the aerodynamic force coincident with the CFD result is proposed. The self-excitation of pitching oscillation and the subsequent limit-cycle oscillation are reproduced in a fine-grid CFD simulation. The axis of the vortex ring in the wake extracted by the phase average is displaced to the lower side of the capsule base when the pitch angle α = 0 and > 0. Such a displacement induced the dynamic component of pitching moment around α = 0. Subsequently, the pitching moment coefficient is decomposed into a Fourier series, where the amplitude of the third harmonics is larger than the dynamic component of the fundamental frequency. The proposed model equation for the pitching moment, which fully includes the third harmonics, reproduces the same amplitude and the same frequency of the CFD result in the case of limit-cycle oscillation. Compared to conventional models, the present model was found to give a better approximation of the dynamic component CMdy of the unsteady aerodynamic work per unit time.