| In recent years,with the rapid development of underwater vehicles,there is an increasing demand for drag reduction by surface flow.Flexible skin drag reduction technology can fit curved surface well without changing shell structure,which is very suitable for surface flow drag reduction of underwater vehicles,thus becoming a research focus in the field of fluid drag reduction.Based on the drag reduction technology of flexible skin,a quasi-periodic elastic support skin structure is proposed,which is characterized by the quasi-periodic arrangement of elastic supports.In the elastic support,two segments with unequal lengths form a periodic unit,forming an approximate periodic arrangement.In this paper,a physical model of quasi-periodic elastic support skin structure is established,and the drag reduction effect of the structure is studied from the aspect of the structure’s influence on turbulence stability.Secondly,this paper discusses the effect of different skin structure parameters on drag reduction,and compares the drag reduction effects of quasi-periodic structure and periodic structure.The work done in this paper mainly includes the following aspects:1)The turbulence stability equation of quasi-periodic elastic support skin surface is established.The physical model of quasi-periodic elastic support skin is constructed.According to the boundary layer small disturbance theory,the turbulent boundary layer small disturbance control equation is established,and the structural control equation is established based on the physical model of the structure.At the same time,the continuous condition of the fluid-solid interface is established at the junction of the skin structure and the fluid.The three constitute the turbulent stability equation,which paves the way for analyzing the stability of the turbulent boundary layer.2)The stability of turbulent boundary layer is analyzed.Chebyshev collocation method is used to discretize the turbulence stability equation.The standard QZ algorithm is used to solve the characteristic equation,and the characteristic curve representing the relationship between the real part and imaginary part of the characteristic value is obtained.The characteristic curves under different damping lengths are analyzed.The analysis results show that the quasi-periodic elastic support skin structure with reasonable value has the ability to inhibit the generation of hydrodynamic unstable waves.3)The velocity distribution of turbulent boundary layer is calculated.Based on boundary layer theory and mixed length theory,the governing equation of velocity distribution is established.The governing equations of velocity distribution in turbulent boundary layer are transformed by implicit difference method.The velocity equation is numerically calculated and the velocity distribution curve of turbulent boundary layer is obtained.The velocity distribution curve is analyzed.The analysis results show that the quasi-periodic elastic support skin structure has the ability to reduce the flow resistance when the anhydrous dynamic unstable wave is generated.4)The characteristics of drag reduction in turbulent boundary layer of skin structure are analyzed.The stability characteristic curves and velocity distribution curves of various parameters of the quasi-periodic elastic support skin structure are analyzed.The results show that the drag reduction effect of skin structure increases with the decrease of elastic support stiffness,flexible wall damping and flexible wall stiffness,and the increase of elastic support spacing,while the drag reduction effect of skin structure is the best when the ratio q=4 between adjacent elastic supports.The characteristic curve,velocity distribution curve and drag reduction rate of quasi-periodic structure and periodic structure are compared.The results show that the drag reduction rate of quasi-periodic structure can be increased up to 1.8% compared with periodic structure under the condition of reasonable parameter values. |
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