Numerical Research On Active Flow Control Of Blended-wing-body Underwater Glider

Blended-wing-body underwater glider has broad application prospects in marine survey and military fields.The lift-drag ratio of the underwater glider has an important impact on its range and economy.Relying only on the optimization of the shape to improve the flow or flow separation state to increase the lift-drag ratio of the underwater glider will narrow its internal space and weaken its detection ability or working time.Therefore,it is of great significance to seek a method that does not rely on the optimization of the shape to improve the lift-drag characteristics of the blended-wing-body underwater glider.Based on the CFD method,this paper conducts numerical research on the two-dimensional and three-dimensional active flow control of the underwater glider,respectively,and explores the influence law and mechanism of the active flow control jet on its lift-drag characteristics from the perspective of the flow field.The specific research contents of this paper are summarized as follows:(1)The establishment of a numerical calculation model for the flow field of the active flow control underwater glider and the verification of the calculation method.With reference to the research status of hydrodynamic characteristics of underwater glider at home and abroad and take into account the flow field characteristics of active flow control underwater glider,and based on the RANS method,a reasonable turbulence model,discrete format,and solving algorithm are selected,and combined with UDF technology,a numerical calculation model for the flow field of the active flow control underwater glider is established,and the calculation method is verified based on experimental data.(2)Numerical study on active flow control of NACA0015 hydrofoil section.The structural grid is divided for the NACA0015 hydrofoil section flow field calculation domain,and the grid independence and time step independence are verified to select a reasonable calculation grid and time step size.Furthermore,the unsteady calculations of the flow field of the section without and with the steady blowing/suction and synthetic jet active flow control are carried out separately.From the perspective of the flow field,the effects and mechanisms of different forms of jets with different positions,different jet deflection angles,different jet ratios or momentum coefficients on its lift-drag characteristics are explored.(3)Numerical study on active flow control of derived NACA0015 hydrofoil section.Based on the numerical study on active flow control of NACA0015 hydrofoil section,the structural grid is also divided for the flow field calculation domain of the derived hydrofoil section of the underwater glider,and the grid independence is verified.Selecting a reasonable number of grid to carry out numerical research on derived NACA0015 hydrofoil section active flow control to explore the active flow control mechanism.And the effects of different types of jet flow control are compared and analyzed.The research results show that when the nozzles of different forms of jets are located on the upper surface of the glider’s sections,different forms of jets can improve the flow state of the hydrofoil sections of the glider at different angles of attack,thereby improving its lift-drag characteristics.Among them,the flow control effect of steady suction is the best.(4)Numerical study of three-dimensional active flow control for underwater glider.Based on the numerical study of the active flow control of the underwater glider’s sections,the steady suction is selected as its active flow control jet.The structural grid is divided for the flow field calculation domain of the underwater glider,and the grid independence is verified.Based on the established numerical model,the unsteady calculations of the flow field of underwater glider without and with steady suction active flow control are carried out,and the flow control mechanism of the underwater glider under different angles of attack is obtained from the flow field perspective.Steady suction can form an effective coupling effect with the incoming flow through local energy injection,which improves the flow state of glider with different angles of attack,thereby improving its lift-drag characteristics,and the lift-drag ratio can be increased up to 78.9%.