Anquan Wang

Photon monte carlo simulation for radiative transfer in gaseous media represented by discrete particle fields

Monte Carlo ray-tracing schemes have been developed for the evaluation of radiative heat transfer for problems, in which the participating medium is represented by discrete point masses, such as the flow field and scalar fields in PDF Monte Carlo methods frequently used in combustion modeling. Photon ray tracing in such cases requires that an optical thickness is assigned to each of the point masses. Two approaches are discussed, the point particle model (PPM), in which the shape of particle is not specified, and the spherical particle model (SPM) in which particles are assumed to be spheres with specified radiation properties across their volumes. Another issue for ray tracing in particle fields is the influence region of a ray. Two ways of modeling a ray are proposed. In the first, each ray is treated as a standard volume-less line. In the other approach, the ray is assigned a small solid angle, and is thus treated as a cone with a decaying influence function away from its centerline. Based on these models, three different interaction schemes between rays and particles are proposed, i.e., line-SPM, cone-PPM and cone-SPM methods, and are compared employing several test problems.

Importance of Combined Lorentz-Doppler Broadening in High-Temperature Radiative Heat Transfer Applications

The importance of combined Lorentz-Doppler (or Voigt) broadening of spectral lines in high-temperature radiative heat transfer applications is investigated. Employing narrow-band transmissivities as the criterion, the critical total pressure below which, and the critical temperature above which Doppler broadening has a significant effect on the absorption coefficient is established for gaseous H 2 O and CO 2

Development of a Coupled DSMC - Particle Photon Monte Carlo Method for Simulating Atomic Radiation in Hypersonic Reentry Flows

With a fast reentry speed, the Stardust vehicle generates a strong shock region ahead of its blunt body with a temperature above 60,000 K. These extreme Mach number o ws are sucien tly energetic to initiate gas ionization processes and thermal and chemical ablation processes. The generated charged particles aect nonequilibrium atomic and molecular energy distributions and shock layer radiation. In this work, we present the rst loosely coupled direct simulation Monte Carlo (DSMC) simulations with the particle-based photon Monte Carlo (p-PMC) method to simulate Stardust reentry o ws in the transitional o w regime. Eleven species including 5 ionization processes were modeled in DSMC, and the average ion velocity model was used to simulate electron motion. At these altitudes, the degree of ionization is predicted to be between 3 - 7 % along the stagnation line, and the maximum translational and electron temperatures are approximately 60,000 K and 20,000 K, respectively. To ecien tly capture high nonequilibrium eects, emission and absorption cross section databases using the Nonequilibrium Air Radiation (NEQAIR) were generated, and N and O radiation was calculated by the p-PMC method. It was found that the N emission is approximately one order of magnitude higher than the O emission along the stagnation line due to the higher concentration of N at this altitude. The radiation energy change calculated by the p-PMC method has been coupled in the DSMC calculations. It was found that while the N and O atomic radiation does not have impact on the o w eld at 81 km, at 68.9 km, the stronger radiation aected the o w eld. The radiation resulted in lowering the gas temperatures in the high emission region, but slight increase of temperatures near the body as well as convective heat ux to the Stardust surface.

Development of Coupled Particle Hypersonic Flowfield-Photon Monte Carlo Radiation Methods

DOI: 10.2514/1.44645 With its fast reentry speed, the Stardust vehicle generated a strong shock region ahead of its blunt body with a translational temperature in excess of 60,000 K. Such an extreme Mach number flow is sufficiently energetic to initiate gas ionization processes and thermal and chemical ablation processes. The generated charged species affect nonequilibrium atomic and molecular energy distributions and shock layer radiation. In this work, we present the first loosely coupled direct simulation Monte Carlosimulations with the particle-based photon Monte Carlo method to simulate high-Mach-number reentry flows in the near-continuum to transitional flow regimes. Eleven species including five ionization processes were modeled in direct simulation Monte Carlo, and the average ion velocity model was used to simulate the electron motion. The degree of ionization is predicted to be between 3–7% along the stagnation line for altitudes of 68.9 and 81 km, and the maximum translational and electron temperatures are approximately 60,000 and 20,000 K, respectively. To efficiently capture the nonequilibrium radiation generated by this flow, emission and absorption coefficient databases using the Nonequilibrium Air Radiation computational tool were generated. However, in contrast to the Nonequilibrium Air Radiation computational tool, radiative transport was modeled by the particle-based photon Monte Carlo method instead of the simplified one-dimensional tangentslab approximation. It was found that the atomic nitrogen emission is approximately 1 order of magnitude higher than the atomic oxygen emission along the stagnation line due to the higher concentration of atomic nitrogen at this altitude.Theradiationenergychangecalculatedbytheparticle-basedphotonMonteCarlomethodwascoupledwith the direct simulation Monte Carlo calculations, and it was found that although the atomic nitrogen and atomic oxygenatomicradiationdoesnothaveanimportantimpactonthe flowfieldat81km,thestrongerradiationmodified the flowfield and heat flux at the wall at an altitude close to peak heating.

Particle Methods for Simulating Atomic Radiation in Hypersonic Reentry Flows

With a fast reentry speed, the Stardust vehicle generates a strong shock region ahead of its blunt body with a temperature above 60,000 K. These extreme Mach number flows are sufficiently energetic to initiate gas ionization processes and thermal and chemical ablation processes. The nonequilibrium gaseous radiation from the shock layer is so strong that it affects the flowfield macroparameter distributions. In this work, we present the first loosely coupled direct simulation Monte Carlo (DSMC) simulations with the particle‐based photon Monte Carlo (p‐PMC) method to simulate high‐Mach number reentry flows in the near‐continuum flow regime. To efficiently capture the highly nonequilibrium effects, emission and absorption cross section databases using the Nonequilibrium Air Radiation (NEQAIR) were generated, and atomic nitrogen and oxygen radiative transport was calculated by the p‐PMC method. The radiation energy change calculated by the p‐PMC method has been coupled in the DSMC calculations, and the atomic...

Monte Carlo Schemes for Radiative Transfer in Media Represented by Particle Fields

Monte Carlo ray-tracing schemes are developed for the evaluation of radiative heat transfer for problems, in which the participating medium is represented by discrete point-masses, such as the flow field and scalar fields in PDF Monte Carlo methods frequently used in combustion modeling. Photon ray tracing in such cases requires that an optical thickness is assigned to each of the point-masses. Two approaches are discussed, the Point Particle Model (PPM), in which the shape of particle is not specified, and the Spherical Particle Model (SPM) in which particles are assumed to be spheres with constant radiation properties. Another issue for ray tracing in particle fields is the influence region of a ray. Two ways of modeling a ray are proposed. In the first, each ray is treated as a standard volume-less line. In the other approach, the ray is assigned a small solid angle, and is thus treated as a cone with a decaying influence function away from its center line. Based on these models, three different interaction schemes between rays and particles are proposed, i.e., Line-SPM, Cone-PPM and Cone-SPM methods, and are compared employing several test problems.Copyright

A k-DISTRIBUTION-BASED SPECTRAL MODULE FOR RADIATION CALCULATIONS IN MULTI-PHASE MIXTURES

k-distribution-based approaches are promising models for radiation calculations in strongly nongray participating media. Advanced k-distribution methods were found to achieve close-to benchmark line-by-line (LBL) accuracy for strongly inhomogeneous multi-phase media accompanied by several orders of magnitude smaller computational cost. In this paper, a k-distribution-based portable spectral module is developed, incorporating several state-of-the-art k-distribution methods along with compact and high-accuracy databases of k-distributions. The module construction is flexible — the user can choose among various k-distribution methods with their relevant k-distribution databases, to carry out accurate radiation calculations. The spectral module is portable, such that it can be coupled to any flow solver code with its own grid structure, discretization scheme, and solver libraries. This open source code module is made available for free for all noncommercial purposes. This article outlines in detail the design and the use of the spectral module. The k-distribution methods included in the module are briefly described with a discussion of their advantages, disadvantages and their domain of applicability. Examples are provided for various sample radiation calculations in multi-phase mixtures using the new spectral module and the results are compared with LBL calculations.Copyright