Effect of hull displacement on hydro- & aerodynamics of a planing trimaran

Abstract

The tunnel hydrodynamic and aerodynamic forces are the key to improve the overall resistance of planing trimaran. The variation of hull displacement has different effect on the tunnel flow characteristics at diverse sailing states, resulting in various change trend of resistance per displacement (R / △) of trimaran at various hull displacement. Combined with model tests, this paper conducts numerical investigation for the detailed analysis of hull displacement effect on the hydrodynamics and aerodynamics of a planing trimaran in various speed ranges. It is found that tunnel air cushion occurs when this trimaran running at low speed. The critical Froude Number of air cushion appearance is strongly influenced by the wave interaction in tunnel, where it may occur earlier at heavier hull load. At semi-planing speed, the difference of hull trim angle mainly accounts for the obvious discrepancy of R / △ of trimaran with different hull loads. Apart from the dominant effect of main hull, the high-pressure region at front tunnel, caused by bow wave washing, also plays a boosting role on enlarging the difference of bow-up trim angle between various load conditions. The heavier hull load leads to the stronger interaction between bow waves of main hull and tunnel at semi-planing speed. After entering planing speed, the tunnel wave crest moves astern more quickly at light-load where tunnel ventilation thus occurs earlier. The air flows through tunnel more smoothly at light load, which weaken the tunnel ram pressure effect in turn. At planing state, the variations of tunnel aero-lift and hydro-lift dominantly influence the different growth trend of trimaran R / △ at various hull loads. This work is helpful for the design and performance prediction of planing trimaran which designed for multi working conditions.