Modeling of the Electric Field in a Hypersonic Rarefied Flow

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83620/1/AIAA-2010-635-332.pd

Simulation of Reactions Involving Charged Particles in Hypersonic Rarefied Flows

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77265/1/AIAA-2009-267-646.pd

Evaluation of Finite-Rate Surface Chemistry Models for Simulation of the Stardust Reentry Capsule

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97086/1/AIAA2012-2874.pd

Modeling Ablation of Charring Heat Shield Materials for Non-continuum Hypersonic Flow

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97121/1/AIAA2012-532.pd

Kinetic Simulation of Rarefied and Weakly Ionized Hypersonic Flow Fields.

When a vehicle enters the Earth's atmosphere at the very large velocities associated with Lunar and Mars return, a strong bow shock is formed in front of the vehicle. The shock heats the air to very high temperatures, causing collisions that are sufficiently energetic to produce ionized particles. As a result, a weakly ionized plasma is formed in the region between the bow shock and the vehicle surface. The presence of this plasma impedes the transport of radio frequency waves to the vehicle, causing the phenomenon known as "communications black out". The plasma also interacts with the neutral particles in the flow field, and contributes to the heat flux at the vehicle surface. Since it is difficult to characterize these flow fields using flight or ground based experiments, computational tools play an important role in the design of reentry vehicles. It is important to include the physical phenomena associated with the presence of the plasma in the computational analysis of the flow fields about these vehicles. Physical models for the plasma phenomena are investigated using a state of the art, Direct Simulation Monte Carlo (DSMC) code. Models for collisions between charged particles, plasma chemistry, and the self-induced electric field that currently exist in the literature are implemented. Using these baseline models, steady state flow field solutions are computed for the FIRE II reentry vehicle at two different trajectory points. The accuracy of each baseline plasma model is assessed in a systematic fashion, using one flight condition of the FIRE II vehicle as the test case. Experimental collision cross section data is implemented to model collisions of electrons with neutral particles. Theoretical and experimental reaction cross section data are implemented to model chemical reactions that involve electron impact, and an associative ionization reaction. One-dimensional Particle-In-Cell (PIC) routines are developed and coupled to the DSMC code, to assess the limitations of the baseline electric field model. Interpretation of the DSMC-PIC results leads to the development of an improved electric field model that does not require the substantial computational resources needed to obtain DSMC-PIC solutions.Ph.D.Aerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/78779/1/efarbar_1.pd

Numerical modeling of the CN spectral emission of the Stardust re-entry vehicle

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90680/1/AIAA-2011-3125-594.pd

Investigation of the Effects of Electron Translational Nonequilibrium on Numerical Predictions of Hypersonic Flow Fields

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90681/1/AIAA-2011-3136-683.pd

Open source Direct Simulation Monte Carlo (DSMC) chemistry modelling for hypersonic flows

An open source implementation of chemistry modelling for the direct simulation Monte Carlo (DSMC) method is presented. Following the recent work of Bird [1] an approach known as the quantum kinetic (Q-K) method has been adopted to describe chemical reactions in a 5-species air model using DSMC procedures based on microscopic gas information. The Q-K technique has been implemented within the framework of the dsmcFoam code, a derivative of the open source CFD code OpenFOAM. Results for vibrational relaxation, dissociation and exchange reaction rates for an adiabatic bath demonstrate the success of the Q-K model when compared with analytical solutions for both inert and reacting conditions. A comparison is also made between the Q-K and total collision energy (TCE) chemistry approaches for a hypersonic flow benchmark case

Modeling of Ablation Using the DSMC Method

Many of the future materials of interest to NASA for atmospheric re-entry are ablators. When a charring ablator is used, thermal pyrolysis of the heat shield material produces an inner gas which then flows through the surface and into the flow field. Additionally, the exposed surface of the material reacts and eventually looses mass and recesses. At high altitude, the latter phenomenon is not dominant, and the majority of the ablative products come from the inner structure of the material. The pyrolysis process starts early in the re-entry trajectory, often when the vehicle has not yet reached the continuum region. In order to model these types of noncontinuum ablating flow fields, the Direct Simulation Monte Carlo (DSMC) method is used. The DSMC method is a kinetic numerical technique that has been used to simulate gas flows in translational, chemical and thermal nonequilibrium for many applications. The DSMC method involves following a representative group of simulated particles throughout the computational domain, as they move and collide. Individual models are employed to account for physical processes, such as chemical reactions, excitation of internal energy modes and gas-surface interactions. In this work, an existing DSMC code is modified to include the injection of a gas with a specified composition and mass flow rate from the vehicle surface into the flow field. The surface-normal velocity components of the injected particles are sampled from a biased Maxwellian velocity distribution at the specified constant surface temperature. As a first step toward the implementation of a fully reacting surface boundary with blowing, the well documented IRV-2 vehicle test case is used to test the new boundary condition. The free stream conditions at an altitude of 67 km are used, with a vehicle velocity of 6780.6 m/s. The Knudsen number, indicating continuum breakdown, is approximately 0.03 based on the nose radius of the vehicle. This places the 67 km flight condition in the non-continuum flow regime. An isothermal wall temperature of 1600 K is imposed, as is a fixed blowing rate of 0.033 kg/m2/s of CO. The influence of the ablation products on the surface heat flux and shock stand-off distance is investigated. Additionally, the DSMC results are compared to results obtained using the CFD code LeMANS. Qualitative agreement between the two sets of results is observed, however there are significant differences in the predicted CO concentration and flow field temperatures. The latter discrepancy is observed in comparisons of DSMC and CFD flow field results