Research On Drag Reduction Mechanism Of Ship Air Curtain In Shallow Water Environment

The resistances on the ship are the main factors of its energy consumption,and the surface friction resistance is the main part of the total resistance of the ship.By injecting gas into the bottom of the ship to form an air bubbles layer,the air flow drag reduction technology can effectively reduce the surface friction resistance of the ship,thereby reducing the total resistance to save fuel.In recent years,with the rapid development of the shipping industry domestic and overseas,especially the river shipping and river-ocean combined transportation.The number of inland ships in China has increased significantly,which makes the increasing energy consumption and environmental protection become a social problem that needs to be solved urgently.In this thesis,the main drag reduction mechanism of air flow drag reduction in shallow water environment is studied by experiment.Firstly,the turbulence suppression mechanism of air flow drag reduction is studied by plate experiment in circulating water tank.The effect of turbulence suppression on air flow drag reduction and the effect of turbulence suppression on the reduction of friction resistance on plate surface are obtained.Finally,it is found that turbulence suppression is one of the main drag reduction mechanisms of air flow drag reduction.In the experiment,the drag reduction effect caused by turbulence suppression accounts for more than 60 % of the total drag reduction effect.Secondly,under the same experimental conditions,the shallow water environment is added to study the change of the drag reduction effect of the air curtain with the distance between the plate and the bottom of the water body under different shallow water conditions.The results show that due to the influence of shallow water environment,the water flow forms a turbulent flow field after flowing through the bottom of the water body.The flow field interacts with the flow field at the bottom of the plate,which affects the flow field of the plate itself,making the flow field on the lower surface of the plate more turbulent and the resistance increases.However,the air flow drag reduction can still reduce the plate resistance effectively in this environment,but compared with the non-shallow water environment,the turbulence inhibition and the drag reduction effect are reduced.Finally,the main mechanism of drag reduction effect of air flow in shallow water environment is analyzed by comparing the difference of flow field between shallow water and non-shallow water environment.The final results show that the turbulence generated by the shallow water environment has a strengthening effect on the turbulence intensity of the plate flow field,and the intensity increases with the decrease of the distance between the plate and the bottom of the water body.The air flow can effectively suppress the turbulence phenomenon of the plate flow field,and the suppression effect is also effective in both shallow and non-shallow water environments.However,the suppression of turbulence by air flow is mainly by inhibiting the formation and development of turbulence,and the suppression effect is reduced by the influence of shallow water flow field,which makes the final drag reduction effect decrease.But in general,the drag reduction is still effective.Finally,according to the experimental results,the empirical formula of ship air flow drag reduction in shallow water environment is established to calculate the drag reduction efficiency.