Experimental Study On The Near Field Jet Characteristics Of Power Law Liquid In Swirl Injectors

The phenomenon of liquid jets breakup exists in daily life and industrial engineering widely.The research on the mechanism of jet atomization is a traditional subject with important theoretical and practical value.Because of the better atomization performance,the swirl injectors are widely used in engineering machinery and rocket engine combustion system in recent years.Researchers have conducted extensive research on the jet breakup process of Newtonian fluid.Due to the complexity of the constitutive equation of power law non-Newtonian fluid,there are few researches on the near field breakup characteristics and lack of detailed theoretical support.The experimental research on the characteristics of power law fluid jet breakup at the near field is of great significance both in theory and engineering applications.In this paper,the gel-type power law fluid was prepared and the optical experiment bench was designed and built.The jet images of the near field region were obtained by using the high-speed photography.The paper investigated the jet parameter,injector geometry parameter and physical parameter on the atomization behaviors of the swirl liquid sheets.X-ray imaging technique was used to obtain the mass fraction distribution of the near field spray.The characteristic parameters such as liquid core breakup length and spray angle were extracted from the X-ray photograph.The influences of different parameters on the mass distribution in near field are carefully studied.The experimental results show that with the increase of injection pressure,the power law fluid swirling jet has five different breakup modes in the near field region: the cylindrical jet mode,the twisted liquid film mode,the open-flow swirling mode,the complete swirling mode and the full development mode.Changes in the test parameters will affect the generation and development of the breakup mode,and some modes will not appear under the certain test conditions.The breakup process of the swirling jet is much more complicated.Different characteristics such as droplet,liquid column,planar liquid film,conical liquid film will appear in turn.The increase of injection pressure is favorable to the swirl jet breakup.The high value of the tangential hole diameter,the aspect ratio and the fluid viscosity all inhibited the swirl jet breakup.The decrease of the orifice diameter will accelerate the swirl jet breakup.But when the orifice diameter is too small,it will go against the breakup process.For the liquid core of the swirl jet,the increase of the injection pressure,and the decrease of the tangential hole diameter,aspect ratio,fluid viscosity will all make the liquid core breakup length decrease and the spray angle increase.The relation between the liquid core breakup length with the orifice diameter and the swirl chamber diameter is complicated.The increase of the orifice diameter and the decrease of the swirl chamber diameter will lead to the increment of the spray angle.The fluid mass fraction distribution is symmetrical along the radial central axis,and three peaks appear during the development.The fluid mass decreases with the increase of injection pressure at the jet center.At the edge of the liquid film,the fluid mass fraction decreases with the decrease of injection pressure.The fluid mass fraction decreased in the axial direction and decreased with the increase of injection pressure.The influence of nozzle geometry parameters on jet mass fraction is more complicated.For the swirl jet which has entered the full development mode,the larger the orifice diameter,the smaller the fluid mass fraction.Outside the swirling jet liquid sheet,the fluid mass fraction decreases with the increase of the tangential hole diameter.For fluids with different viscosities,the greater the viscosity,the greater the mass fraction in the near field region.And the greater the concentration,the more pronounced the mass distribution symmetry of the fluid in the radial direction.