PREFACE

Tremendous amounts of research results have been accumulated to the information pool for plasmadynamics and plasma, which is the most common state of matter in the universe by either mass or volume. The underlying physics occurs mostly at the molecular and atomic scales and often under an extremely high enthalpy condition or in a strong electromagnetic field; these phenomena must be analyzed by physics-based modeling. The research progress faces formidable challenges because the compositions of non-equilibrium-ionized gas are always in transient quantum states where the fundamental chemical-physics processes are the least understood. Furthermore, the validating experimental data are also very sparse.

In spite of these limitations, thousands of conference papers and articles on this subject are still persistently releasing to the open literature annually. Meanwhile, the electromagnetics is increasingly recognized to broadening physical dimensions for interdisciplinary science and technology to meet engineering requirements. For the rapidly advancing scientific field, outstanding and fundamental technical references are published mostly in the period from the middle 1960s to later 1980s. Although all these illuminating accomplishments have withheld the test of time but have not been updated by converting information into knowledge for practical engineering applications. It is appropriate and timely that summarization of these impressive scientific accomplishments and a systematic review on the progress of this scientific discipline are needed for future development.

The inherent nature of interdisciplinary computational electromagnetic-aerodynamics links five major scientific disciplines from aerodynamics, electromagnetics, chemical-physics kinetics, plasmadynamics, to computational modeling and simulations. The knowledge of each individual discipline has been developed over centuries and numerous treatises on these subject areas have been published and firmly established for understanding. There are also some path-finding articles in classic magnetohydrodynamics that detail the magnetic field-dominated astrophysics around 50 years ago, but none have been documented for computational electromagnetic-aerodynamics to reach a comprehensive status in providing a practical working knowledge. For this reason, an attempt is made here to integrate these pertaining disciplines to supply a working knowledge for engineering and to suggest the best practice in applications. Hopefully this effort can be a viable reference for professional development and graduate studies.

The text is organized in 10 chapters, with the first three chapters consisting of introductions to fundamental knowledge of plasmadynamics, chemical-physics of ionization, formulations of classical magnetohydrodynamics, and their extension to low magnetic Reynolds number electromagnetic-aerodynamics conditions. In fact, most plasma-based flow control actuators, high-speed flows of interplanetary reentry, and ion thrusters in space exploration are operating under this environment.

For fundamental knowledge, a brief review of unique features of the plasma medium is presented in terms of the Debye shielding length, Coulomb and Lorentz forces, Joule heating, plasma frequency, and plasma waves. All these unique characteristics of ionized gas in an electromagnetic field are intermediately related to outstanding engineering applications of computational electromagnetic aerodynamics. Then the statistical thermodynamics that bridges the microscopic to macroscopic thermodynamics is introduced for the ionization processes. The mechanisms of photoionization, thermal excitation, and electron impact ionization are discussed on the basis of the most recent research findings.

The hierarchal relationship among fundamental formulations for plasmadynamics and their valid domains of approximation is outlined and reviewed next. The basic assumptions for the classic magnetohydrodynamics formulation are articulated, and detailed derivations from ideal to full magnetohydrodynamics equation, as well as the low magnetic Reynolds number equations system, are delineated. These governing equations, in fact, define the limitations and physical fidelity of all computational simulations. From the eigenvalues and eigenvectors analyses of the magnetohydrodynamics equations, correlations are revealed between propagating speeds of Alfven, entropy, contact surface, slow and fast plasma waves.

A peculiar property of plasma in an electromagnetic field is that it does not exist as an unrealistic one-dimensional phenomenon. Therefore, the shock jump condition must be formulated, at least by tangential and normal components across a discrete wave. The simplest shock in the electromagnetic field is essentially a two-dimensional oblique wave. When the macroscopic conservative equation is integrated across the shock, and it requires that the normal components of the magnetic flux density and the tangential component of the electric field intensity are continuously across any interface. As a consequence, the Rankine-Hugoniot relationship of gas dynamics across a shock is significantly modified in an ionized gas to become a unique feature of the plasma medium.

The next three chapters of the book provide in-depth and specific descriptions of numerical algorithms and procedures for solving Maxwell's equation in the time domain for computational electromagnetics, plasma wave propagation, and fluid dynamics. All these detailed numerical algorithms and computational procedures are the shared knowledge for the interdisciplinary computational modeling and simulation science and technology. The highlights are especially placed on overlapping areas of technical issues and realizable application opportunities.

Two major foci of the present objective are to integrate the interlinking computational modeling and simulation techniques of aerodynamics and electromagnetics. To make the procedure tractable, the computational approach is further restricted to the continuum regime so the approach is built on the frameworks of the time-dependent Maxwell equations and the compressible Navier-Stokes equations. It should be recognized that the Maxwell equations constitute the hyperbolic partial differential system and belong to a class of bondless initial-boundary-value problems. This unique feature poses a fundamental dilemma for all numerical analyses that must be carried out in a finite-size computational domain. However, the characteristic-based formulation can alleviate this constraint by achieving an invariant dependent variables grouping in the domain of dependence. This formulation permits all propagating electromagnetic waves exit through numerical boundary unimpeded. The computational electromagnetics technique is applying to the microwave propagation in waveguide, plasma wave diffraction and refraction, as well as the plasma diagnostic technique by microwave attenuation beyond Langmuir probes.

The last four chapters are focused on the modeling and simulation techniques for computational electromagnetic-aerodynamics. The most current progress in computational electromagnetic-aerodynamics is summarized for multifluid models, including chemical kinetics by nonequilibrium thermal excitations, chemical physics by electron impact ionization, transport property by gas kinetics, and numerical algorithms. The emphases are on the physical fidelity of computational models that describe the behavior of the direct current charge, dielectric barrier charges, microdischarge, and their interactions with aerodynamics through the mechanisms of Joule heating and Lorentz forces. Transport property by drift motions and diffusions of the charged particle is also described by the classical drift-diffusion theory. The interface boundary conditions between the chemically reacting media and solid surface are derived together with the requirements on electrodes in an externally applied electric field. The latter are described in detail in conjunction with the discharging electric circuit equation. On this frame of analysis, the secondary emission of electrons from the cathode, together for the self-limiting feature of dielectric barrier discharge by preventing transit to arc, is unambiguously illustrated. For the thermal ionizing model, the models of internal degrees of freedom for vibration relaxation and electron excitations are also described at practicing level. Some of the innovative numerical procedures are also included as bench marks for future progression.

It is important to acknowledge that the electromagnetic effect in most flow control applications appears only as a small perturbation. In general, the relative magnitude of aerodynamic inertia overwhelms the electromagnetic force by a thousand fold. In terms of magnetic Reynolds number for an electromagnetics-aerodynamics field that is measured by the ratio of inertia and the product of electric conductivity and magnetic permittivity , its magnitude is much smaller than unity. The plasma-based actuators are therefore observed to be the mostly effectiveness for flow control at a critical point of a bistable aerodynamic state or to the high-frequency, low-amplitude oscillations. Thus, aerodynamic phenomena are singling out for possibly enhancements by infusing electromagnetic effects. For this purpose, the aerodynamic bifurcations of viscous-inviscid interaction, including flow separation, self-sustained oscillation, vortical dynamics, and hydrodynamic instability leading to turbulent...