Wake structure in high-speed flow of a rarefied plasma over a body

Abstract

In the study of qualitative features of flow of a rarefied plasma over bodies in ionospheric aerodynamics, the problem of flow behind a two-dimensional plate is often considered. The formulation of this problem and its relation to flow over real objects was considered in detail in [1], This model problem has been analyzed in a number of papers using two main approaches: description of the flow with the help of the similarity solution found in [2, 3], and numerical solution of the equations of plasma motion [4–7]. A review of the main results obtained by the two methods can be found in [1, 6]. This paper gives a numerical solution of the problem of transverse supersonic flow over a flat plate. The plasma is assumed to be collisionless and is described by the kinetic equation with a self-consistent field. The particle-in-cell method is used to solve the kinetic equation. In contrast with most numerical calculations previously performed [4–6], the present paper considers the case, of greater practical interest, of flow over a body whose dimension R is much greater than the Debye radius Di in the unperturbed plasma. Practically all the known results for this case have been obtained using the similarity solution [2, 3], which is not valid, however, in the entire region of unperturbed flow, and therefore does not give a complete solution to the problem. Individual numerical calculations (see [7]) do not add much to the similarity analysis, since they refer to a very narrow range of the flow parameters. The main emphasis in the present paper is the study of wake structure behind a flat plate and plasma instability in the wake. The computations were performed in a wide range of variation of the ratioβ=Te/Ti, and one can follow the processes of ion acceleration, interaction of the accelerated group of ions with the plasma, development of beam-type instability [1, 8], and formation and decay of the turbulent wake. The qualitative wake structure features discussed below are also found, of course, in plasma flow over actual three-dimensional bodies.