Pulse injection of cold gas in the separation zone occurring on the surface of a rotation body at its hypersonic MHD overflow is simulated. Previously (see, in particular, [1,2]), we have shown that at the dipole configuration of the magnetic field generated by currents flowing inside the body the MHD interaction can lead to the formation of extensive separation zones with practically motionless medium. Flow streamlines skirt the separation zone along the magnetic lines of force. It is of importance that in this zone the heat flux density to the body surface decreases. It has been revealed that it is possible to control the position and size of the separation zone on the body surface by changing the direction and intensity of the dipole magnetic field moment. In this connection it is of interest the possibility of the directional impact on the medium in the separation zone without its destroying, in particular, its cooling by a cold gas pulse injection.
The problem is solved in two formulations. In the first of them the body is an infinite cylinder with axis perpendicular to the incident flow velocity vector. Two parallel wires are disposed in the cylinder. The electric currents in the wires flow in opposite directions closing at infinity. The moment of the dipole magnetic field generated by the currents is normal to the incident flow velocity vector as well as to the cylinder axis. In the second formulation the body is a sphere in which a circular current coil is located. The magnetic dipole moment is directed along the incident flow velocity vector. The initial conditions for the corresponding unsteady problems are the stationary solutions without injection obtained in the MHD model taking into account the induced magnetic fields, viscosity, thermal conductivity and real thermodynamic properties of air. The incoming flow pressure and density correspond to the atmosphere parameters an altitude of 65 km, the body velocity is 7 km/s. The injected gas (air) has the wall temperature (2000 K). Its velocity is 300 m/s; the pressure is equal to the pressure in the near wall area. The mass of the gas injected per pulse is close in magnitude to the mass of medium in the separation zone before the injection.
The study conducted shows that the injection of cold gas into the separation zone leads to the cooling of this region (Fig 1) accompanied by a decrease of total heat flux into the body. This effect persists for a long time after the injection completion (Fig 2), although the injected gas partially flows from the separation zone into the external flow. As seen from a comparison of the solutions, the observed phenomenon is not qualitatively dependent on the location of the separation zone, but expressed more clearly if this zone is in the shock layer.
Figure 1. The temperature and velocity vector diagram: to the left – cylinder (17 ms after the injection completion, the injection zone is from -23° to +23°, the angle is measured from the front stagnation point); to the right – sphere (36 ms after the injection completion, the injection zone is from 82° to 105°). The injection duration is 5 ms.
Figure 2. The time dependence of the total heat flux into the cylinder (left panel) and the sphere (right panel)
1. Е.V. Gubanov, A.P. Likhachev, S.A. Medin. Hypersonic MHD flow over rotation body at finite magnetic Reynolds numbers // In: Proceedings of the 10th Workshop on Magneto-Plasma Aerodynamics. Ed. V.A. Bityurin, Moscow, JIHT RAS, 2011. P. 342-348
2. Е.V. Gubanov, A.P. Likhachev, S.A. Medin. On the sphere MHD overflow with separation zones at finite magnetic Reynolds numbers // In: Proceedings of the 11th Int. Workshop on Magneto-Plasma Aerodynamics. April 10 – 12, 2012. Moscow, Russia. Ed. V.A. Bityurin. JIHT of RAS, Moscow. 2012. P. 312-319
