Study On Drag Reduction Technology Of Long-voyage Underwater Glider

Autonomous underwater glider(AUG)is a new kind of underwater vehicle,which is widely used in the field of ocean exploration.However,with the depth and breadth of marine research continuing to expand,people put forward higher requirements for diving depth and endurance of marine equipment.The key of the Long-voyage underwater glider is to save energy and reduce consumption besides using large capacity battery.Reducing the drag of the glider is an important way to save energy and reduce the consumption.Therefore,the drag reduction technology of underwater glider is studied in this dissertation to provide a technical basis for improving the voyage of underwater glider.Firstly,the drag reduction technology and its development status of underwater glider are introduced.At the same time,computational fluid dynamics(CFD)method is used to analyze the water resistance of gliders at different speeds and different attack angles.It is pointed out that the water resistance coefficient of the whole underwater gliders is more larger than that of the other underwater vehicles.Friction drag has taken up a large part of the total drag,and pressure drag is also obvious.According to the pressure distribution,velocity contour,turbulent kinetic energy and surface shear stress,a conclusion is drawn that different drag reduction technologies should be adopted for different parts of gliders.In this dissertation,drag,drag coefficient and drag reduction ratio are used as evaluation indexes for drag reduction effect of gliders.Secondly,shape drag reduction,groove drag reduction and super hydrophobic drag reduction of glider are studied.In the aspect of shape drag reduction,the drag reduction effect of different length to diameter,different types curve,and the same type curve with different parameters are studied through simulating.It is determined that the Myring curve with length to diameter of head and tail being 1.875,length to diameter of the whole glider being 10.875,head parameter being 2 and tail parameter being 25° is used as the shape of Long-voyage underwater glider,which can reduce the drag by 6.5%.In the aspect of groove reduction,the drag reduction effect of semicircular,rectangular and symmetrical "V" three different shapes are compared by simulating.The law of action of drag reduction on the symmetrical "V" groove with feature size ? and ,the top angle of the groove and the groove layout direction are studied.The symmetrical "V" groove with depth 0.487 mm,width 0.709 mm,top angle 70 degrees,and direction of the groove layout of 40 degrees to water flow is arranged on the wing of Long-voyage underwater glider model,which the drag reduction effect is 2% by simulation analysis.There are two ways to achieve super hydrophobic drag reduction.The pool towing test of glider with hydrophobic coating proves that the drag reduction effect of hydrophobic coating paint is 4%~9%,but the coating is unstable and easy to fall off.It is proved by simulation that the super hydrophobic surface can achieve 7%~9% drag reduction effect on gliders.The test shows that the super hydrophobic surface is stable under pressure,temperature,salt and time tolerance.The error of drag coefficient calculated by simulating with setting up the slip speed is 3%~5% comparing with the drag coefficient obtained by falling experiment,so the simulation results above for the super hydrophobic surface of the glider are effective.Finally combining three kinds of drag reduction methods,this dissertation put forward an optimal and reliable drag reduction method for Long-voyage underwater glider.The minimum drag Myring shape is applied to the whole glider.Micro-groove is applied to the wing of the glider,and super hydrophobic surface is applied to the body of the glider,which achieves 13.1% drag reduction effect of the whole glider by simulating.