Experimental Study On The Viscous Effect Of Rayleigh-taylor Instability On Liquid-liquid Oblique Interface

Rayleigh-Taylor(RT)instability is a common phenomenon in fluid mechanics.It refers to the random small perturbation at the interface when the light fluid is accelerated by the continuous acceleration and the pressure density does not coincide with the density gradient,p0? ??(27).It will result in the turbulent mixing after the linear phase and the nonlinear phase.Kelvin-Helmholtz(KH)instability is an interface instability induced by shear force because of the difference of velocity at a non-uniform density interface.The problem of coupling different interface instability is not only have important theoretical value in revealing the physical mechanism of interface instability,but also have important value in engineering applications such as engine internal combustion chambers,and also exist in astronomical dynamics such as supernova explosion.Recently,under the background of how to carried out implosion ignition in inertial confinement nuclear fusion,it has been the focus of scholars.Baroclinic effect is one of the important factors inducing interface instability.How to analyze the influence of baroclinic effect on RT-induced interface instability is a classic problem in interface instability.The problem of the coupling effect between RT instability and KH instability on the interface evolution is a competing relationship or a mutual promotion problem is also plagued by scholars.The viscosity of fluid as an important physical parameter of fluid,like surface tension,has always been considered as a physical quantity that inhibits the unstable development of the interface,but whether the viscosity is the same as other physical quantities in the induction mechanism,such discussion only shows the theory and numerical values.Simulation studies have little support for experimental research in this area.Therefore,the following research work has been carried out on the above points:(1)By varying the pressure in the high pressure section,two different accelerations are obtained.The high-speed schlieren method is used to observe the evolution of the interface instability under different accelerations.A large number of experimental results show that the growth law of perturbation in mixed zone is different under different accelerations.The parameters of the mixing zone are defined,and the relationship of the width and angle of the mixing zone with time are quantitatively analyzed.The initial dip of the interface only affects the development of the width of the mixing zone in the later stage of evolution under the same acceleration.When the width of the mixing zone no longer increases,the angle of the mixing zone is still growing on the tilted interface.(2)In the case when the initial interface inclination angle is 5°,by using different viscous as light fluids,three different viscosity ratio of fluid combinations are obtained.And the mass fraction of the heavy fluid potassium iodide solution is changed,so that the Atwood number is 0.169.A large number of experimental results show that the increase of viscosity will inhibit the number and development of the initial perturbation.When the fluid is most viscous,the surface of the mixed zone becomes smoother in the later stage of evolution,which is similar to the theory of bubble merge that found in domestic and foreign counterparts.Under the same conditions of others,only the initial dip angle of the interface is increased to study the interaction between different baroclinity and turbulence induced interface instability.The flow field is also observed by the high-speed schlieren method.A large number of experiments are carried out to ensure the repeatability of the experiment,and the flow field development image is obtained.The results show that when the fluid is in the same viscosity,the growth amplitude of the perturbation is about the same,and the way of development in the mixed zone structure is also same.The initial interface inclination angle increases,due to the constraint of the wall surface,the tendency of the mixing zone to turn over increases,and the interface is overturned.(3)The dimension appearing in the experiment was dimensionlessly processed,and the growth law of the width and angle of the mixing zone was found.The width growth of the mixing zone was fitted.The relationship between the growth rate of the mixing zone and the viscosity ratio and the initial interface inclination angle was found.The statistical analysis of the angle growth mode of the mixing zone shows that the angle of the mixing zone is asymptotically linear with the evolution displacement.(4)The PIV-PLIF synchronous measurement technology was built by using the slice light technology.The velocity-concentration distribution at different moments in the flow field at the center of the flow field was experimentally studied,and the fluid particle motion map and fluorescence map were obtained.The Matlab programming language is used to analyze the information in the field,and the related information such as the density distribution map is obtained.