Aerothermodynamics of atmospheric entry

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Computational and experimental studies of high-altitude spacecraft aerothermodynamics are planned. The prospects of current evolution of aerospace engineering are associated with the development of a new generation of re-entry space vehicles and hypersonic transport vehicles. It is impossible to develop such vehicles without solving some basic problems of hypersonic flight mechanics, which are primarily related to physicochemical and radiation gas dynamics of high-velocity flows. They are critically important for creating future aerospace vehicles. Experimental modeling in this field is extremely expensive in terms of materials and financing. This problem will be partly solved by means of modeling a steady flow as a pulsed flow, which is provided by using equipment and diagnostic methods of LEMPUS gas-dynamic facilities of the Novosibirsk State University and requires much smaller amounts of energy and consumables. The governing role in such studies, however, is given to numerical simulations. New numerical methods for investigation of high-altitude altitude spacecraft aerothermodynamics at the kinetic level will be developed and tested, especially in terms of reliability of modeling non-equilibrium physical and chemical processes. Numerical tools developed on the basis of the new methods will be used for a detailed study of aerothermodynamics of perspective aerospace vehicles.

Continuum methods cannot be applied to describe flows at high flight altitudes because of the strong rarefaction of the atmosphere at these altitudes. In this case, it is necessary to use a kinetic description of the flow, based on the Boltzmann equation. The most popular approach to solving the Boltzmann equation is the Direct Simulation Monte Carlo (DSMC) method, which is now the main tool for studying complicated multidimensional rarefied gas flows. The main constraints in using the kinetic approach are currently related to insufficient detail and physical adequacy of models used to describe various collision processes: dissociation, vibrational relaxation, ionization, etc., especially for flow parameters corresponding to spacecraft descent with Earth’s escape velocity.

More reliable (as compared to currently existing models) new molecular models that describe collision processes in high-velocity reacting flows for the DSMC method will be developed within the framework of this project, tested, and applied to solve particular aerothermodynamic problems. Based on these models, a computer code will be developed for computing high-altitude aerothermodynamics of space vehicles by the DSMC method on hybrid computational clusters with computational nodes generated on central (CPU) and graphical (GPU) processor units. Modeling of real gas effects in a new software system will be based on new molecular models. Testing of numerical methods and verification of the software system will be performed by comparisons with results of modern experimental studies of high-enthalpy laminar flows and with in-flight test results. Laminar separated flows near aerodynamic control surfaces of the spacecraft at high altitudes will be numerically investigated, and the influence of real gas effects on the structure of separated flows will be studied. Aerothermodynamics of reentry capsules of promising space vehicles (including situations of vehicle descent with superorbital speeds) will be numerically studied with allowance for real gas effects. Integral aerothermodynamic characteristics of these vehicles, as well as force and heat loads distributed over the vehicle surface will be determined for different flight altitudes.

An important task of high-altitude aerothermodynamics is reduction of heat fluxes and control of motion of re-entry vehicles. Along with the currently known methods for controlling the wave drag (pullout aerodynamic needle, blowing of gas jets, liquid and solid particles into the incoming flow, the laser spark ahead of the body), whose basic idea is to create a flow similar to that past a pointed body, a new approach to managing aerodynamic characteristics of blunt bodies using gas-permeable porous materials is proposed. Interaction of supersonic and hypersonic flows with gas-permeable materials is poorly studied. Participants of the project have started experimental and numerical study of this phenomenon, which offers great promise for development of new and effective methods of flow control. The use of gas-permeable porous materials allows us to create a specified aerodynamic shape of the aircraft, using the structure of the material and controlling the viscosity of gas in the pores. This will improve the performance of control systems compared to traditional methods of control surfaces. It is planned to perform a computational and experimental study of flow around a cylinder parallel to supersonic flow with gas-permeable material mounted on its frontal surface. The experimental study will be conducted in the hypersonic wind tunnel T327B at Mach number M = 5. Mesh screens and cellular-porous materials with different spatial structure and porosity will be used as gas-permeable materials. Experimental studies will be complemented by numerical simulations. In particular, parametric calculations will be carried out to find the optimal structure of the materials and the internal temperature field.

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