Yaw effect on bi-stable air-wakes of a generic ship using large eddy simulation

Abstract

An LES (large eddy simulation) investigation at Re=8×104 has been conducted to predict the flow past a simplified frigate shape model at yaw, of which the stern is analogous to a double backward-facing step. At 0∘ yaw, the occurrence of a double bi-stable flow configuration is recorded, i.e. an asymmetrical flow topology is observed behind each step, and the flow configuration at the flight deck (top step) is anti-symmetrical as compared to the rear step. Even when the incoming flow is yawed with a small angle (e.g. ±2.5∘), the bi-stable flow configuration is still present and the level of the asymmetry is increased at each step. Moreover, the negative angle maintains the same flow configuration as what is shown at 0∘ yaw, while the positive angle leads to the corresponding anti-symmetrical flow configuration. A larger yaw angle suppresses this asymmetrical flow topology on both steps. To explore those asymmetrical phenomena, a brief analysis and discussion are included for each case, showing that the direction of the incoming flow and the length of each step are key parameters that characterise this double bi-stable behaviour.