Effect of sound-absorbing coatings on the disturbance evolution in a flow of a mixture of vibrationally excited gases

Abstract

Abstract. The flow around a solid plate and a plate with a sound-absorbing coating at a nonzero angle of attack in a hypersonic flow (М=8.44) of a mixture of vibrationally excited carbon dioxide and nitrogen is considered. Numerical simulations are performed by solving twodimensional unsteady Navier-Stokes equations with a two-temperature model of relaxing flows. The vibrational energy as a function of time is defined by the Landau−Teller equation. A skeleton model, which is a set of square elements arranged in a staggered order, is used for simulating the porous coating made of foamed nickel with a porosity coefficient of 95%. The distance between the elements is equal to the pore diameter of the real sound-absorbing material. Data on the evolution of disturbances on the solid plate and on the plate with the soundabsorbing coating are presented for various angles of attack and CO2 concentrations in the mixture. The experimental and calculated data on pressure fluctuations on the plate surfaces are found to be in good agreement. The effects of various parameters of the sound-absorbing coating (depth, length, and location at the flat plate) are considered. It is shown that the soundabsorbing coating significantly reduces the intensity of pressure fluctuations on the plate surface as compared to the solid surface (up to 50% depending on the length and location of the sound-absorbing coating). IntroductionThe possibility of controlling the intensity of disturbances in boundary layers and the transition to turbulence is one of the important aspects of the development of perspective hypersonic aircraft. Real gas effects associated with excitation of vibrational degrees of freedom of molecules and flow nonequilibrium are manifested under real flight conditions, where high speeds and temperatures are observed. Real gas properties can significantly affect the generation and evolution of disturbances in the boundary layer and, as a consequence, the transition to turbulence. Nowadays large scientific experience has been accumulated in studying the effect of physical and chemical processes in gases on the mean flow around bodies at hypersonic velocities [1]. However, there are only a few papers on stability of such flows (e.g., [2][3][4]).Disturbances formed in the shock layer are carried downstream and affect the evolution of disturbances and the laminar-turbulent transition in the hypersonic boundary layer on a model. One of the known methods for controlling the laminar-turbulent transition in moderately hypersonic flows is the method of applying a sound-absorbing coating onto the surface [5]. The method of sound-absorbing coatings has proved its effectiveness for low-temperature flows at М=21 [6]. It is shown [7] that the method of sound-absorbing coatings is also effective in hypersonic flows of vibrationally excited carbon dioxide. However, the intensity of relaxation processes and their influence on the evolution of disturbances in a mixture with other gases can differ from the processes in pure CO2.The present res...