NUMERICAL INVESTIGATION OF HYPERSONIC INVISCID AND VISCOUS FLOW DECELERATION BY MAGNETIC FIELD

The present article is devoted to the analysis of various aspects of magnetohydrodynamic (MHD) control over supersonic and hypersonic flow deceleration. The complicated flow structure (shock waves, boundary layer separation, recirculation zones) is simulated with the aid of numerical solution of axisymmetric Navier-Stokes equations for laminar and turbulent flows. Along with the flow field analysis, the deceleration process characteristics are estimated for the wide range of MHD interaction parameter. The special attention is focused on the question concerned with irreversible losses. The MHD effects and boundary layer interaction give rise to the unusual effects concerned with MHD interaction parameter influence on the deceleration process efficiency. Recently some proposals [1-8] to use the MHD-devices for flow control in hypersonic vehicle-propulsion system are discussed. Promising suggestions exist concerning MHD effects use for the improvement of hypersonic propulsion system efficiency. These suggestions have their bases on the possibility to develop the special devices (using modern technologies) for flow pre-ionization before the vehicle or at the entrance to the propulsion system. The flow preionization is complex technical problem. The large technical efforts are directed on its solution. One way to create the air stream conductivity by apparatus on the vehicle board has been studied in detail previously [5]. However the following development of technical work applied to hypersonic propulsion system requires precise understanding of possible advantageous of MHD control in itself. In spite of study undertaken, the clarity in this question is not yet conclusively established. Therefore these aspects of MHD control efficiency are of primary importance. It is necessary to estimate the existing proposals of MHD control not only qualitatively, but quantitatively as well. The flow field in the hypersonic propulsion system is too complex. The new physical models must be developed and included into the existing computational models of the flow in hypersonic propulsion system to study the efficiency of MHD control applied to hypersonic propulsion. Furthermore, it seems to be appropriate to solve some simplified model problems to understand main flow features and to estimate the efficiency of the supersonic and hypersonic flow control by MHD methods in the range of parameters typical for hypersonic propulsion systems. The possibility of MHD flow control in the duct of hypersonic propulsion system and flow structure are investigated now in CIAM on the base of the combined mathematical model [9]. This combined model includes as constituents the gasdynamics, turbulence and supersonic combustion models. This model is supplemented by the physical models for the description of MHD flow. The existing preceding experience in MHD flow investigation [10] is used and adapted to new applications. The present article is devoted to the analysis of various aspects of MHD control over supersonic and hypersonic flow deceleration. The following schemes of the MHD control will be discussed. The first of them is concerned with supersonic flow deceleration by axisymmetric magnetic field. The structure of the flow in axisymmetric duct at the supersonic flow deceleration by magnetic field, generated by current loop or solenoid, is investigated. The complicated flow structure (shock waves, boundary layer separation, recirculation zones) is simulated with the aid of numerical solution of axisymmetric Navier-Stokes equations for laminar and turbulent flows. Another scheme of MHD control is also investigated. This scheme provides the supersonic flow deceleration in 2-D channel when magnetic field is perpendicular to the flow plane and, depending on wall electric properties, electric energy may be extracted from the duct. The exact problem including coupled system of 2-D electromagnetic field equations and 2-D gasdynamic equations with MHD terms is solved. Along with exact model, the simplified flow model based on local quasi 1-D electrodynamics and 2-D gasdynamics with MHD terms is used. The applicability of simplified model is analyzed by comparison with exact model solution. It is necessary to note that corroboration of positive influence of MHD effects on the hypersonic propulsion system performances was made in the first stage, as a rule, on the base of simplified flow models and this was justified in the stage of effects revealing. The 1-D inviscid MHD approach was used in this analysis in many cases [6]. Some results [4,5,7] concerning both flow over aerodynamic body [4] and inlet flow [5,7] were obtained within 2-D Euler equations for inviscid gas. However, it was shown in previous investigations that viscous effects are very important in typical MHD systems [11]. Therefore it is necessary to estimate the role of