Numerical Simulation And Control Methods Of The Frigate Airwake

Helicopters' landing on the frigate is more dangerous than the same situation on the ground,especially on the middle or small class frigates.Because of the complicated flow structures in the stern flow field of the ship,the stability of helicopter landing is greatly affected,which threatens the safety of helicopter seriously when taking-off and landing on the frigate.Therefore,the research on the frigate airwake is carried out to analyze the formation mechanism and complex flow field structure of the frigate airwake,and to improve the helicopter landing environment by studying the flow control technology,so as to improve the safety of the helicopters' landing.The research can provide important reference for the engineering study.In this paper,the computational fluid dynamics software CFD++ is used to simulate the typical frigate using the Detached-eddy Simulation(DES)method based on the Spalart-Allmaras turbulence model.A comprehensive validation exercise has been performed by comparing with the experiment results,it is found that the velocity distribution of the steady-simulation results is quite different from the experiment results,however,the unsteady-simulation results agree well with the experiment results,which verifies the reliability and accuracy of the numerical simulate method adopted in this paper.Based on this,the formation mechanism and unsteady characteristics of the frigate airwake are analyzed in detail.At the same time,an analysis of the airwake flow topology at headwind condition highlights the vortex pairing process which dominates the flowfield above the deck.Additionally,the influence of hangar-door state(open,closed or half-open)on the airwake was also investigated in detail.It is found that the effect of hangar-door state on frigate airwake is not that obvious,except when hangar-door half opened the turbulence kinetic energy at the deck away from the hangar is the smallest.And simulations were made by adding blowing or suction devices on flight deck or hangar to alter the ship airwake for purpose of the improvement of safety when launching and recovering of helicopters to naval ships,the results showed that the flow control method can effectively control the region of recirculation zone and downwash velocity component.Meanwhile,the research on the characteristics of frigate ship airwake influenced by three different hanger shapes for a headwind and the Green 45° case is carried out.The results showed that equal height hangar shapes were not conducive to the safety when launching and recovering of helicopters to naval ships,compared by the same hanger height but with both lower sides.By reducing hangar height reasonably,the launching and recovering environment on flight deck could be improved.At last,the results verified the validity of the empirical equation for the prediction of the range of the recirculation zone.The empirical equation provide an important reference for the engineering study.