Research On Speediness Improvement Of A Waterjet-propelled High-speed Landing Ship

Traditional landing-transport ship which with flat bow and transom stern have advantages of large load capacity and shallow draft,but the service speed is low.To reduce the hull resistance,a longitudinal tunnel was introduced on the ship bottom,and a high power density water-jet was used instead of the original propeller propulsion for ship speediness improvement.Through the drainage effect of tunnel,the high-pressure area of ship bow decreased,and thus improved pressure distribution on ship bottom.The form of tunnels was divided into two types: the local one located in the ship bow,and the longitudinal one throughout the ship bottom.To investigate effects of the local tunnel shape on the drag reduction,a variety of tunnel shapes(with different tunnel length,width,and the top plate form)was used.The mass flow was controlled by changing longitudinal tunnel's roof angle and shape.In order to improve the hull propulsive efficiency of high speed,a high power density water-jet was used instead of the traditional propeller for ship propulsion.By adopting ship bottom tunnel and water-jet,the ship rapidity capacity was improved well.The flow around landing-transport hull was numerically simulated by CFD method.To speed up the CFD calculation,the Body Force Method was introduced for replacing the impeller part of water-jet system.Hull resistance was obviously decreased with tunnels set up on the ship bottom,and the mass flow of tunnel is the main factor which affects drag reduction.As the drainage volume of tunnel increasing,the pressure difference between bow and stern reduced significantly,but the draft increased meanwhile can also affect the drag reduction effect of frictional resistance.To adjust the mass flow of tunnels,a folded plate form was used as the tunnel roof in this study.When the angle point of roof was located in hull medium,the landing craft reached a 24.07% drag reduction at the speed of 30 kn.To some extent,the negative thrust deduction brought by water-jet propulsion at high speed also contribute to the hull resistance decreasing.By using the tunnel and water-jet propulsion,the landing craft reached a 25.17% drag reduction at the speed of 30 kn.