Flow-induced vibrations of a hinged cavity at the rear of a blunt-based body subject to laminar flow

We perform numerical simulations to characterize the flow-induced vibrations (FIV) of a rear cavity with elastically hinged rigid plates, placed as a passive device at the base of a blunt body that is subject to a laminar flow of Reynolds number Re=400. The dynamic response and forcing of plates, wake features and force coefficients are investigated for the range of reduced velocity U*=[0,30]. Three different regimes of the rotational oscillations are identified. An initial branch of low oscillation amplitude is defined for U*fn. Additionally, a multibody model has been developed to retrieve, from the plates rotational motion, the resultant forces and moments that produce the plates vibration. Such inverse dynamics model is formulated to allow its generalization for configurations of higher dynamical order, and validated against the results obtained from the numerical simulations. The analysis shows that the synchronization regime is mainly promoted by a reduced fluid damping and a forcing moment that acts in phase with the plates motion. The switch in such phase from 0∘ to 180∘ occurs after the lock-in, what attenuates the plates response at large U*. In general, the FIV of plates alters the vortex shedding and near wake pressure, especially during the synchronization regime, inducing an overall increase of the global force coefficients with respect to the static cavity. Thus, the performance of hinged plates enhances generally the mean drag, although a 25% reduction is reported for the lift amplitude.