Joseph S. Shang

Modeling of ac dielectric barrier discharge

The qualitative electrodynamic field of the dielectric barrier discharge in air is studied by a three-component, drift-diffusion plasma model including the Poisson equation of plasmadynamics. The critical media interface boundary conditions independent of the detailed mechanisms of surface absorption, diffusion, recombination, and charge accumulation on electrode or dielectrics are developed from the theory of electromagnetics. The computational simulation duplicates the self-limiting feature of dielectric barrier discharge for preventing corona-to-spark transition, and the numerical results of the breakdown voltage are compared very well with data. According to the present modeling, the periodic electrodynamic force due to charge separation over the electrodes also exerts on alternative directions from the exposed to encapsulated electrodes over a complete ac cycle as experimental observations.

Simulating Hypersonic Magnetofluid-Dynamic Compression in Rectangular Inlet

The combined effects of an electromagnetic perturbation and viscous-inviscid interaction generate a high-pressure plateau near the hypersonic leading edge surface. The surface pressure induced by magnetofluid-dynamic interaction emulates a movable leading edge strake. This phenomenon has been verified in experimental research, which shows that a direct current surface discharge becomes a virtual compression ramp for flow control. More recently, investigation has extended to a rectangular hypersonic inlet. The present analysis solves the magnetofluid-dynamic equations using weakly ionized gas models, including the formulation based on the drift-diffusion theory. The numerical simulation provides a detailed description of the intriguing magnetofluid-dynamic interacting flowfield. After validation by experimental measurements, the computed results quantify the effectiveness of a magnetofluid-dynamic compression for a hypersonic inlet. Applying a plasma generation power input to a direct current surface discharge of 7.87 W per square centimeter of electrode area, the interaction produces an 11.7% higher compression of a constant cross-section inlet.

Computational electrodynamic simulation of direct current discharge

A drift-diffusion model for simulating direct current discharge including the externally applied magnetic field is analyzed by a high-resolution, diagonally dominant numerical procedure. Three different configurations of direct current discharge were studied numerically—the electrodynamic structures of the classic parallel electrodes of infinite and finite dimension, as well as the side-by-side electrode configurations. In the final configuration, an externally applied transverse magnetic field has also been applied in computational simulation to study the Lorentz force effect to the discharge structure. The solutions were compared to classic results, similar numerical simulations, and experimental observations of the discharge physics. Overall, the agreement is very good and the model can be used as a basis for the design of flow control experiments.

Solving Schemes for Computational Magneto-Aerodynamics

The electromagnetic force introduces a new physics dimension for enhancing aerodynamic performance of aerospace vehicles. In order to simulate interdisciplinary phenomena, the Navier–Stokes and Maxwell equations in the time domain must be integrated on a common frame of reference. For a wide range of applications from subsonic unmanned vehicles to hypersonic flight control, the resultant nonlinear partial differential equations offer a formidable challenge for numerical analysis. The experience and physical insight using the approximate Riemann and compact-differencing formulation as well as several temporal discritizations will be shared. The most recent development and advancement in numerical procedures for solving this system of governing equations are delineated

A computational approach for hypersonic nonequilibrium radiation utilizing space partition algorithm and Gauss quadrature

An efficient computational capability for nonequilibrium radiation simulation via the ray tracing technique has been accomplished. The radiative rate equation is iteratively coupled with the aerodynamic conservation laws including nonequilibrium chemical and chemical-physical kinetic models. The spectral properties along tracing rays are determined by a space partition algorithm of the nearest neighbor search process, and the numerical accuracy is further enhanced by a local resolution refinement using the Gauss-Lobatto polynomial. The interdisciplinary governing equations are solved by an implicit delta formulation through the diminishing residual approach. The axisymmetric radiating flow fields over the reentry RAM-CII probe have been simulated and verified with flight data and previous solutions by traditional methods. A computational efficiency gain nearly forty times is realized over that of the existing simulation procedures.

Spherical harmonics method applied to the multi-dimensional radiation transfer

Abstract The spectral radiation transfer equation in 2D axisymmetrical and 3D geometries is solved by the P 1 -approximation of the spherical harmonics and ray-tracing methods. Martian atmosphere and typical entry conditions are considered. Navier–Stokes equations coupled with the nonequilibrium vibrational excitation and finite rate chemistry describe thermodynamically and chemically nonequilibrium gas. The multi-group model is used to model optical properties of CO 2 –N 2 mixture. The developed methodology of integration of the P 1 -approximation on unstructured grids and subsequent numerical solution allow us to reach reasonable agreement with the accurate ray-tracing method and drastically reduce the cost of solution of the radiation transfer equation in multi-dimensional geometries.

Analysis of Hypersonic Nonequilibrium Flow over Ablating Surface

The initial values and boundary conditions of an ablating surface are studied using different kinetic models for calculating the external species concentration of nonequilibrium air over the intensively reacting interface. From the high-temperature air composition, an assessment of the existing chemical kinetic models for a carbonaceous ablator has been made for possible efficiency and accuracy improvements. A formulation of the boundary conditions on the interface has also been derived from the governing equation system to clearly separate aerodynamic simulation from the computational surface thermochemistry. This set of boundary conditions will be adopted as the theoretical base for sustaining research in ablation.

Simulating Plasma Microwave Diagnostics

Computational simulation of plasma diagnostics via microwave absorption has been successfully accomplished. This simulation capability is developed from solutions to a combination of the three-dimensional Maxwell equations and the generalized Ohm’s law in the time domain. As the simulation procedure developed, numerical results were obtained for a range of plasma transport properties including electrical conductivity, permittivity, and plasma frequency. The present results reveal the wave reflection at the media interface and substantial distortion of the electromagnetic field within a thin plasma sheet from a guided microwave. The present numerical simulation also accurately predicts the microwave blackout phenomenon as the wave propagates through a thick plasma sheet. The diffractions and refractions occurring at antenna apertures and passing through a plasma column are captured numerically. Finally, the numerical simulation has successfully duplicated a plasma diagnostic experiment in a hypersonic magneto-hydrodynamic channel.

Three-dimensional Radiative Heating of Descent Space Vehicle Based on Spherical Harmonics Method with Unstructured Grids

The P1-approximation of a spherical harmonics method is used to calculate the three dimensional radiative transfer in emitting and absorbing media for Martian descent space vehicle. The three dimensional governing system of equations describes the flow of viscous, heat conductive, chemically nonequilibrium and radiating CO2-N2 gas mixture. Detailed spectral model is used to calculate the forebody and afterbody radiative heating of capsule. Unstructured tetrahendronal grids are applied to build first order implicit scheme of radiation heat transfer equation. For this purpose highly effective iterative algorithm is applied to resolve sparse system of linear equations. Verification of presented algorithm is provided by tedious and accurate ray-tracing calculations.

Plasma dynamics for aerospace engineering

Charge conservation law, 76, 149 Charge number density, 75 Charge particle mobility, 32 Chemical equilibrium condition, 186 Chemical reaction constant, 198– 199 Backward reaction, 198 Forward reaction, 198 Chernyi et al. Ionization model, 206 Collision Cross section, 108– 109, 113, 115, 117, 151, 190, 251, 255, 306 Complex wave number, 290 Constitutive relationship for electromagnetic variables, 77– 78 Coulomb logarithm kinetic model, 206 Coulomb’s law, 4, 5 Counterlowing plasma jet injection, 369– 371 Long penetration monde, 370 Short penetration mode, 370 Cutoff frequency of wave guide, 48 Cyclotron/ Larmor frequency, 8 Cyclotron/ Larmor radius, 9