Abstract
Recent experiments have demonstrated that tip vortices can trigger the ventilation formation around a surface-piercing hydrofoil. However, the influence of this ventilation on transient flow structures and vortex evolution remains unresolved. This paper numerically investigates the tip-vortex-induced ventilation formation for a surface-piercing hydrofoil at a stalled yaw angle. The predicted unsteady ventilated cavities with tip vortices and pressure-side spray are in reasonable agreement with experimental observations. The ventilation formation process can be divided into three stages: base ventilation, tip-vortex ventilation, and suction-side ventilation. It is indicated that ventilation has a greater impact on the lift coefficient than the drag coefficient. The lift coefficient increases during the base ventilation and tip-vortex ventilation stages due to the expansion of the low-pressure stalled flow, but decreases in the suction-side ventilation stage because of the gradual replacement of this low-pressure region by an aerated cavity. Tip-leakage and tip-separation vortices initially exist independently at the hydrofoil tip, then expand and merge through air ventilation, ultimately forming a strongly stable tip vortex. Furthermore, ventilation promotes vortex generation, with the major contributors being the vortex stretching and baroclinic torque terms.
Funder
National Natural Science Foundation of China
international partnership program of chinese academy of sciences
Subject
Condensed Matter Physics,Fluid Flow and Transfer Processes,Mechanics of Materials,Computational Mechanics,Mechanical Engineering