Study On Influence Of Jet Hole Structure On Drag Reduction Of Underwater Jet Plate

With the rapid development of the social economy,energy and environmental issues have become increasingly prominent,and the ship transportation industry is facing unprecedented challenges.At home and abroad,the problems of high consumption and heavy pollution in the shipping industry are also receiving more and more attention.At present,bubble drag reduction technology has become one of the important techniques for ship drag reduction.By injecting air bubbles into the bottom surface of the ship,a bubble layer is formed on the bottom surface of the ship to change the flow state of the turbulent boundary layer,which can effectively reduce the friction of the bottom surface of the ship resistance.The gas is sprayed into the surface of the bottom of the ship through the jet hole,and the shape of the jet hole and the state of the jet have a certain influence on the drag reducing effect.In order to solve this problem,this topic studies the influence of the structure of the jet orifice on drag reduction.Aiming at the effect of the jet hole structure on the drag reduction effect,we proposed a new cat’s ear-shaped jet orifice with obvious drag reduction effect,and the effect of jet orifice angle and jet velocity on drag reduction are studied.In this paper,the three-dimensional single-jet orifice jet plate is used as the research object.The Mixture multiphase flow model and the k-ε turbulence model are used to simulate the environment required for jet drag reduction.The cylindrical jet orifice,the dilated jet orifice and the cat’s ear-shaped under different parameters are simulated respectively.The drag reduction of the cat’s ear-shaped jet orifice plate and the partial drag reduction effect of the plate along the inflow direction are analyzed in detail.The result shows that the cat’s ear-shaped jet hole with an inclined angle of 15° and an expansion angle of 40° reduces the resistance most significantly.For the cylindrical jet orifice,the different jet angles(20°,25°,30°,35°,40°,45°,60°,90°)and the jet velocity(1.5 m/s,2.5 m/s,5 m/s)were studied.In the case of drag reduction,it is determined that 20° is the best jet angle for drag reduction and 1.5 m/s is the jet velocity with the best drag reduction effect.In view of the drag reduction effect of jet plate with multiple jet holes,the influence rule of spanwise hole spacing ratio and flow-direction hole spacing ratio on drag reduction of jet plate was analyzed,and the best drag reduction effect of hole spacing ratio was determined.In this subject,a three-dimensional multi-jet jet plate with multiple holes is taken as the research object to simulate and analyze the drag reduction effect of a jet plate with a single row jet hole spacing ratio of L1/D0 = 1.5,2,2.5,3,(L1 is the spanwise spacing between the two holes,and D0 is the exit diameter of the jet hole)and a double row jet hole spacing ratio of L2/D0 = 1.5,2,2.5,3,3.5,and 4(L2 is the flow direction spacing between two holes).The results show that with the single-row jet hole,as the hole spacing ratio increases,the drag reduction rate decreases.In the case of multiple rows of jet holes,as the hole spacing increases,the drag reduction rate first increases and then decreases.When L2/D0 = 3.5,the drag reduction rate is the highest.