Study On The Design And Performance Of A Ground Effect Craft Hover System

The air cushion ground effect craft is a kind of triphibian craft that can work on land,on water,or in air,and has three modes of operation,namely,air cushion vehicle mode,ground effect vehicle mode and short-term low altitude flight mode.Ground effect crafts are usually composed of a fuselage and an air cushion system,and skirt is most common component of modern air cushion system.Skirts can be divided into two types:closed bag without fingers,and non-closed bag with capsule fingers.The closed bag without fingers does not wobble during the flight and helps with the flight stability,but comes with poor performance on water;in comparison,the non-closed bag with fingers has excellent performance on water,but wobbles in air and is a severe threat to flight stability.For this reason,a novel skirt system needs to be specially design for the air cushion ground effect craft so ensures the performance both on water and in air.In addition to the bag,the arrangement of the air cushion ground effect craft is different from conventional air cushion crafts because the fans are located in the front as to arrange the cabin and wing structures.Thus a new air duct system needs to be designed so as to have a desired air pressure in the cushion and to avoid adverse trim and plunge-in.Emission height,i.e.the clearance between the lower edge of skirt and the supporting surface,directly affects the lifting power and resistance of hull,small emission heights are more prone to contact the water surface and resulting higher calm water resistance;large emission heights,on the other hand,requires higher lifting power and result in more weight of the craft.Therefore,the relationship between the emission height and fan flux needs to be investigated for the use of overall design of the craft.Given this background,the following research work is carried out in this study:(1)Conceptual design of the ground effect craft hover system.According to the requirements of the hovercraft skirt,the form and main particulars of the skirt are determined.Then a retractable skirt system is designed taking into account of the factors including retractability,air-lock,machinery etc.The retractable skirt system is validated through a demonstrative model test.The parameters of the skirt components,including the geometrical dimensions of the bag and fingers,are determined using empirical formula.3D models are created and CFD simulations are performed as to find out a proper air duct.This design is completed and will be used for the analysis of performance.(2)Study on the static hovering performance on the rigid ground.Numerical models are created and simulations are performed to obtain the fan air fluxes at given emission height.The relationship between the flux and the emission height is then obtained by means of interpolation.This relationship,obtained with CFD numerical simulation,is then validated against empirical formulation.(3)Study on the static hovering performance on still water.The model of the craft hovering on still water is created,and CFD simulations with the unconstrained vertical motion of the craft are performed to obtain the emission heights and trim for given fan air fluxes.The relationship between the fan air flux and emission height are obtained for the craft hovering on still water,and the obtained results are compared and validated against those by empirical formula.