A. F. Kolesnikov

Study of Quartz Surface Catalycity in Dissociated Carbon Dioxide Subsonic Flows

The stagnation point heat transfer from subsonic dissociated carbon dioxide flows to quartz and cooled metallic surface has been studied experimentally and numerically. The experiment was performed by using the induction plasmatron of 100 kW power at pressure 0.1 atm in the wide enthalpy range 14.4-38.5 MJ/kg. The numerical simulation included the computations of the carbon dioxide plasma flows in the plasmatron discharge channel, the flows around the model and within nonequilibrium boundary layer. The data on the effective efficiency of catalytic recombination reactions O + O -» 02 and CO + O -» CO2 on quartz surface have been obtained at the surface temperature range 390-1470 K from comparison of experimental and numerical data on the heat transfer. It is established that effective catalycity of quartz surface in dissociated carbon dioxide flows is quite similar to the data obtained in dissociated pure oxygen flows.

Conditions of simulation of stagnation point heat transfer from a high-enthalpy flow

The problem of local simulation of stagnation point heat transfer to a blunt body is solved within the framework of boundary layer theory on the assumption that the simulation subsonic high-enthalpy flow is in equilibrium outside the boundary layer on the model, while the parameters of the natural flow are in equilibrium at the outer edge of the boundary layer on the body. The parameters of the simulating subsonic flow are expressed in terms of the total enthalpyH0, the stagnation point pressurepw and the velocityV1 for the natural free-stream flow in the form of universal functions of the dimensionless modeling coefficientsξ=Rm*/Rb* (ξ ≤ξ.<1),ζ=V1/√2H0ξ (ζ ≤ ζ.<1) whereRm* and Rb* are the effective radii of the model and the body at their stagnation points. Approximate conditions for modeling the heat transfer from a high-enthalpy (including hypersonic) flow to the stagnation point on a blunt body by means of hyposonic (M≪1) flows, corresponding to the case ζ2≪1, are obtained. The possibilities of complete local simulation of hypersonic nonequilibrium heat transfer to the stagnation point on a blunt body in the hyposonic dissociated air jets of a VGU-2 100-kilowatt induction plasma generator [4, 5] are analyzed.

Determination of the Effective Probabilities of Catalytic Reactions on the Surfaces of Heat Shield Materials in Dissociated Carbon Dioxide Flows

The effect of heterogeneous catalysis on the heat transfer to cold and heated surfaces in subsonic dissociated carbon dioxide jet flows is studied experimentally, using a 100 kW inductive plasma generator, and simulated numerically. The effective probabilities of the heterogeneous reactions CO + O → CO2 and O + O → O2 on molybdenum (Tw=300 K) and quartz (Tw=470–620 K) surfaces, the Buran heat shield tile coating (Tw = 1470—1670 K), and two oxidation-resistant carbon-carbon coating materials (Tw=1420—1840 K) are determined by comparing the experimental and calculated data on the heat fluxes at the stagnation point of models at a pressure of 0.1 atm.

Mathematical Models for Plasma and Gas Flows in Induction Plasmatrons

High frequency induction (electrodeless) plasmatrons provide the wide possibilities for modeling of nonequilibrium processes of dissociated gas flow thermochemical interaction with a surface at the conditions corresponding to hypersonic vehicle’s flight in atmosphere at high altitude [1].

Numerical analysis of simulation accuracy for hypersonic heat transfer in subsonic jets of dissociated nitrogen

One-dimensional problems of the flow in a boundary layer of finite thickness on the end face of a model and in a thin viscous shock layer on a sphere are solved numerically for three regimes of subsonic flow past a model with a flat blunt face exposed to subsonic jets of pure dissociated nitrogen in an induction plasmatron [1] (for stagnation pressures of (104–3·104) N/m2 and an enthalpy of 2.1·107 m2/sec2) and three regimes of hypersonic flow past spheres with parameters related by the local heat transfer simulation conditions [2, 3]. It is established that given equality of the stagnation pressures, enthalpies and velocity gradients on the outer edges of the boundary layers at the stagnation points on the sphere and the model, for a model of radius Rm=1.5·10−2 m in a subsonic jet the accuracy of reproduction of the heat transfer to the highly catalytic surface of a sphere in a uniform hypersonic flow is about 3%. For surfaces with a low level of catalytic activity the accuracy of simulation of the nonequilibrium heat transfer is determined by the deviations of the temperatures at the outer edges of the boundary layers on the body and the model. For this case the simulation conditions have the form: dU∘e/dx∘=idem, p0=idem, Te=idem. At stagnation pressuresP0≥2·104N/m2 irrespective of the catalycity of the surface the heat flux at the stagnation point and the structure of the boundary layer near the axis of symmetry of models with a flat blunt face of radius Rm≥1.5·10−2 m exposed to subsonic nitrogen jets in a plasmatron with a discharge channel radius Rc=3·10−2 m correspond closely to the case of spheres in hypersonic flows with parameters determined by the simulation conditions [2, 3].

Effects of catalytic recombination on the surface of metals and quartz for the conditions of entry into the Martian atmosphere

Heat transfer to water-cooled surfaces of metals and quartz is studied experimentally in subsonic jets of dissociated carbon dioxide at a stagnation pressure of 80 hPa and enthalpy of 9 and 14 MJ/kg, corresponding to the descent conditions of the ExoMars space vehicle into the Martian atmosphere, using an RF induction plasmatron at the Institute for Problems in Mechanics, Russian Academy of Sciences. The measurements of heat fluxes to surfaces of different materials showed the significant effect of the catalytic properties of surfaces that can be arranged in the following descending order of the heat flux: silver, copper, stainless steel, quartz. The effect of strong modification of the silver surface is recorded during the tests; the maximum value of the heat flux is achieved after 15-min exposure of the surface to the jet. In the computational analysis of heat transfer, we used a two-parameter model of heterogeneous recombination of O atoms and CO molecules at the surface. With this model, the effective recombination coefficient of CO molecules is determined on the water-cooled surfaces of quartz and stainless steel, based on the experimental data on heat fluxes.

Similarity between the heat transfer to a model in an underexpanded dissociated-air jet of a high-frequency plasmatron and to a sphere in a high-velocity flow in the terrestrial atmosphere

On the basis of the local heat transfer modeling concept the parameters of supersonic flow past a cylindrical flat-faced model, 0.01m in radius, in an underexpanded dissociate-air jet of the VGU-4 high-frequency plasmatron are recalculated to the conditions of sphere entry in the terrestrial atmosphere. The heat transfer parameters, similar in the experiment and the atmospheric entry, are determined.

Stefan-Maxwell relations for ambipolar diffusion in a two-temperature plasma with application to the problem of an ion-sonic wave

The Stefan-Maxwell relations, in which the concentration gradients are expressed in terms of linear combinations of the diffusion velocities of the components and the thermodynamic parameter gradients, are derived for a partially ionized quasineutral multicomponent two-temperature gas mixture. It is shown that a component of the diffusion driving force proportional to ▿ln(Te/Th), where Te is the electron temperature and Th is the gas temperature, can develop in the two-temperature mixtures. A generalization of the Fick law for the diffusion ion flow which contains the new thermal diffusion force is obtained for a three-component plasma. Under the assumption that the charged components have no effect on the shock wave structure, for linear approximations of the gas density and temperature profiles in this zone approximate mass ion concentration distributions in a shock wave propagating through weakly ionized argon and ahead of its front are analytically obtained under the condition that the electron temperature is much higher than the gas temperature. Analytic distributions of the ambipolar electric field Ea and the ratio Ea/n in the ion-sonic wave (extended zone ahead of the shock wave front in the non-isothermal plasma) are obtained.

Heat Transfer in Subsonic Flows of Dissociated Nitrogen: HF Plasmatron Experiment and Numerical Simulation

Experiments on heat transfer in subsonic jets of dissociated nitrogen have been carried out on a IPG-4 induction plasmatron. The heat fluxes to copper, stainless steel, nickel, graphite, and quartz surfaces at the stagnation point of a water-cooled cylindrical flat-faced model 20 mm in diameter and dynamic pressures have been measured at a pressure of 50 hPa in the test chamber and a power of 35–65 kW of the HF generator. The experiments showed the influence of surface catalytic properties on the heat flux in relation to the nitrogen atom recombination. In the conditions of the experiments, a numerical simulation of nitrogen plasma flows in the discharge channel of plasmatron and the subsonic dissociated nitrogen jet flow around the cylindrical model has been carried out. The experimental and calculated data on heat fluxes to cooled copper, stainless steel, nickel, graphite, and quartz surfaces are compared. The quantitative catalyticity scale of the studied materials in relation to the heterogeneous recombination of nitrogen atoms is established.

Efficient Approach to Description of Heat Transfer and Multicomponent Diffusion in Ionized Gases

The formulas for the heat fluxes of heavy components and electrons as well as the Stefan–Maxwell relations for the diffusion fluxes in amagnetic field are derived for amulticomponent two-temperature plasma with regard to the higher-order approximations in orthogonal expansions of the component distribution functions in Sonine polynomials. For the complex transport coefficients of heavy components and electrons exact formulas are obtained in the significantly simpler form as compared with the standard procedure of the Chapman–Enskog method with the minimum number of minimum-order matrix inversions.