Study On Stability And Breakup Of An Annular Swirling Viscous Liquid Sheet

Pressure swirling atomizers are wildly used in the fuel injection systems in aeroengines, marine engines, vehicle gasoline direct injection engines and gas turbines, et al. Liquid jet stability has decisive role in breakup and atomization of liquid jet. By taking a pressure swirling atomizer as the research object, the stability of an annular swirling viscous liquid sheet is studied. Research works in this dissertation deepen the understanding of the stability and influence factors and influence rules of an annular swirling viscous liquid sheet, provide evidence for controlling and using of an annular swirling viscous liquid sheet.The stability dispersion equation of an annular swirling viscous liquid sheet with solid vortex swirling velocity distribution under three dimensional non-axisymmetric disturbances is established. The dispersion equation is solved numerically in spatial mode. Para-sinuous and para-varicose dominant mode analysis, swirling stability analysis, the effect of liquid viscosity on an annular swirling viscous liquid under non-axisymmetric disturbances analysis, the effect of liquid swirling on the role of surface tension in liquid sheet stability analysis, the effects of surface tension and annular sheet curvature on the sheet swirling stability are studied on the basis of the established equation. The dominant mode of an annular swirling viscous liquid sheet, the effects of liquid swirling strength, gas axial movements around the liquid sheet, liquid viscosity, surface tension and annular liquid sheet curvature on the stability of an annular swirling viscous liquid sheet are determined clearly.An m order non-homogenous modified Bessel equation is solved analytically with the method of variation of parameters. The analytical solution of energy governing equation, boundary conditions and the dispersion equation of an annular swirling viscous liquid sheet under temperature disturbance are deduced. The existence and uniqueness of solution of the dispersion equation of an annular swirling viscous liquid sheet under temperature disturbance are proved. Stability analysis of an annular swirling viscous liquid sheet under temperature disturbance is carried out. The effect of temperature disturbance on maximum disturbance growth rate, most unstable frequency, unstable cutoff frequency and the dominant mode of the liquid sheet, the effects temperature difference between liquid and ambient gas, Peclet number and surface tension variation rate on stability of an annular swirling viscous liquid sheet under temperature disturbance are determined clearly.Second order governing equations and second order boundary conditions of an annular swirling viscous liquid sheet with solid vortex swirling velocity distribution under three dimensional non-axisymmetric disturbances are deduced. And the second order dispersion equation which describes the stability of the annular swirling viscous liquid sheet is derived. On the basis of the established dispersion equation, the effects of first-order and second-order disturbances on the stability of an annular swirling viscous liquid sheet, the effect of aerodynamics on interface stability of an annular viscous liquid sheet and nonlinear stability of an annular swirling viscous liquid sheet are studied. The role of nonlinear stability theory in predicting breakup of an annular swirling viscous liquid sheet, the effect of aerodynamics on an annular viscous liquid sheet interface stability, and the effects of liquid swirling strength, gas-to-liquid density ratio, annular liquid sheet curvature and liquid viscosity on the interface evolution and breakup length are determined clearly.Number based droplet size and velocity distribution of an annular swirling viscous liquid sheet is studied based on maximum entropy method. Joint probability density function of droplet size and velocity distribution of an annular swirling viscous liquid sheet is reduced based on maximum entropy method. The joint probability density function of droplet size and velocity is discussed. Analysis of droplet size and velocity distribution characteristics of an annular swirling viscous liquid sheet, the relativity between droplet size distribution and droplet velocity distribution, the effects of droplet collision and evaporation of droplet size distribution range and peak value are determined clearly.Experimental system of pressure swirling atomizer liquid sheet stability research is set up. The extraction method of pressure swirling atomizer liquid sheet oscillation frequency based Fourier transform and the extraction method of liquid sheet shape, breakup length and cone angle based on photography method are proposed. On the basis of these, the stability of pressure swirling atomizers is studied experimentally with the laser diffraction technique and photography method. The pressure swirling atomizer liquid sheet shape under different liquid volume flow rates, liquid physical properties and atomizer exit inner diameters are studied. And the influence rules of liquid volume flow rate, liquid physical properties and atomizer exit inner diameter on oscillation frequency, breakup length and cone angle of pressure swirling atomizers are determined clearly.