13 results on '"Levin, Deborah A."'
Search Results
2. Kinetic modeling of fluid-induced interactions in compressible, rarefied gas flows for aerodynamically interacting particles.
- Author
-
Marayikkottu, Akhil V. and Levin, Deborah A.
- Subjects
- *
MACH number , *GAS flow , *DRAG force , *GAS distribution , *INTERIM governments - Abstract
In the study of gas-particulate multiphase systems, the flow of high-speed gas through a distribution of solid particulates is of utmost importance. While these aerodynamically interacting systems have been extensively studied for low-speed gas flows in the gas continuum regime, less attention has been given to high-speed systems where non-continuum effects are significant due to the high flow gradients. To address this, the flow of rarefied gas through an aerodynamically interacting monodisperse spherical particle system is studied using the Direct Simulation Monte Carlo (DSMC) gas-kinetic approach. Since the method provides the best resolution of shocks at supersonic Mach numbers it is used to classify the weak separated shocks and strong collective shocks in these systems based on particle spacing in a two-particulate system at different orientation angles. The study used the two-particle system to help analyze more complex particle distributions of volume fractions, 1%, 5%, and 15%, exposed to gas flows in the slip and transitional gas regime for a free-stream Mach number range of 0. 2 < M a ∞ < 2. 0. We observe that the weak separated shocks in the 1% distribution allow a higher degree of gas penetration and shock-particle interactions or " hypersonic-surfing ", exposing a major fraction of the particulates to higher force magnitudes. In contrast, the strong collective shock in the 5% and 15% distributions only generates high particulate forces on the flow-facing particles. Finally, a simple stochastic model is proposed for use in large-scale Eulerian–Lagrangian simulations that captures the non-monotonic behavior of average drag and force variability generated by the complicated gas particulate interactions in the compressible gas regime. [Display omitted] • Study on high-speed gas flow through particulates, emphasizing non-continuum effects. • DSMC classifies shocks in particle systems, varying particle spacing and orientation. • ' Hypersonic surfing " in 1%, strong collective shocks in 5%, 15% distributions. • Model for simulations to capture gas-particulate interactions in compressible regime. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
3. Prediction of gas transport properties through fibrous carbon preform microstructures using Direct Simulation Monte Carlo.
- Author
-
Jambunathan, Revathi, Levin, Deborah A., Borner, Arnaud, Ferguson, Joseph C., and Panerai, Francesco
- Subjects
- *
CARBON , *MICROSTRUCTURE , *MONTE Carlo method , *GASES , *HYDRAULICS - Abstract
Highlights • Predicted gas transport properties using an integrated kinetic computational framework. • Analyzed the effect of material anisotropy on the permeability and pore-scale velocity. • Pore-diameter computed in this work agreed well with tomography derived data. • Determined representative elementary volume (REV) required for material characterization studies. Abstract We use the Cuda-based Hybrid Approach for Octree Simulations (CHAOS) DSMC solver to predict gas transport coefficients of Morgan felt and FiberForm TPS materials with sample size of (1 × 1 × 1) mm3. The detailed velocity flow-field of the pressure-driven flow through these materials is studied to compare the effect of material microstructures on gas transport. It is found that the effective flow path traversed by the gas is more circuitous and longer for FiberForm compared to the more porous felt. The obstruction offered by the material and the circuitous flow path is quantified by the Klinkenberg-derived permeability and hydraulic tortuosity factor, which are key material properties that govern the momentum transport through porous media. We also compute the hydraulic pore diameter of these materials and find that the through-thickness and in-plane pore diameter is equal to 86.94 and 98.7 μ m for felt and 36.25 and 60.9 μ m for Fiberform, which is within 5–6% of the average pore-size obtained from the tomography images. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
4. Modeling of Near-Continuum Laminar Boundary Layer Shocks Using DSMC.
- Author
-
Tumuklu, Ozgur, Levin, Deborah A., Gimelshein, Sergey F., and Austin, Joanna M.
- Subjects
- *
CONTINUUM mechanics , *NITROGEN , *LAMINAR boundary layer , *HYPERSONIC flow , *GAS flow , *ENTHALPY , *MATHEMATICAL models - Abstract
The hypersonic flow of nitrogen gas over a double wedge was simulated by the DSMC method using two-dimensional and three-dimensional geometries. The numerical results were compared with experiments conducted in the HET facility for a high-enthalpy pure nitrogen flow corresponding to a free stream Mach number of approximately seven. Since the conditions for the double wedge case are near-continuum and surface heat flux and size of the separation are sensitive to DSMC numerical parameters, special attention was paid to the convergence of these parameters for both geometries. At the beginning of the simulation, the separation zone was predicted to be small and the heat flux values for the 2-D model were comparable to the experimental data. However, for increasing time, it was observed that the heat flux values and shock profile strongly deviated from the experiment. Investigation of a three-dimensional model showed that the flow is truly three-dimensional and the side edge pressure relief provides good agreement between simulations and the experiment. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
5. Factors Influencing Flow Steadiness in Laminar Boundary Layer Shock Interactions.
- Author
-
Tumuklu, Ozgur, Levin, Deborah A., Gimelshein, Sergey F., and Austin, Joanna M.
- Subjects
- *
LAMINAR boundary layer , *SHOCK waves , *HYPERSONIC flow , *THERMOCHEMISTRY , *MONTE Carlo method - Abstract
The Direct Simulation Monte Carlo method has been used to model laminar shock wave boundary interactions of hypersonic flow over a 30/55-deg double-wedge and "tick-shaped" model configurations studied in the Hypervelocity Expansion Tube facility and T-ADFA free-piston shock tunnel, respectively. The impact of thermochemical effects on these interactions by changing the chemical composition from nitrogen to air as well as argon for a stagnation enthalpy of 8.0MJ/kg flow are investigated using the 2-D wedge model. The simulations are found to reproduce many of the classic features related to Edney Type V strong shock interactions that include the attached, oblique shock formed over the first wedge, the detached bow shock from the second wedge, the separation zone, and the separation and reattachment shocks that cause complex features such as the triple point for both cases. However, results of a reacting air flow case indicate that the size of the separation length, and the movement of the triple point toward to the leading edge is much less than the nitrogen case. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
6. Advanced parallelization strategies using hybrid MPI-CUDA octree DSMC method for modeling flow through porous media.
- Author
-
Jambunathan, Revathi and Levin, Deborah A.
- Subjects
- *
PARALLEL computers , *MESSAGE passing (Computer science) , *OCTREES (Computer graphics) , *VECTOR spaces , *POROUS materials , *MONTE Carlo method - Abstract
The advantages of a linear space filling Morton Z-curve to represent an unbalanced three-dimensional octree structure for the Direct Simulation Monte Carlo method are assessed. The strategies to optimize and exploit the properties of the linearized tree using simple, binary computations are presented. Hybrid MPI-CUDA communications are invoked to facilitate the use of heterogeneous architectures for large-scale computations. Strong scaling studies have shown that the parallelization strategies implemented in this work results in 85% efficiency, and weak scaling studies show nearly 100% efficiency for a problem size with 0.34 billion particles and 1.5 million immersed body surface elements. Two types of problems, supersonic external flow over fractal-like immersed body and subsonic internal flow through a porous material are solved using the multi-GPU DSMC solver. The permeability of Morgan carbon felt material is calculated by modeling the diffusion of argon gas through the material and the calculated continuum permeability values match well with published data. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
7. Direct Simulation of Argon Condensation Flow Using a Kinetic Evaporation Model.
- Author
-
Jiaqiang Zhong and Levin, Deborah A.
- Subjects
- *
PHYSICS research , *CONDENSATION , *EVAPORATION (Chemistry) , *ARGON , *KINETIC theory of gases , *MONTE Carlo method - Abstract
A cluster evaporation model was derived from the classical nucleation theory (CNT) in the previous work to simulate condensation in free expanding plumes using the direct simulation Monte Carlo (DSMC) method. However, the use of a CNT evaporation model, especially in a low temperature environment, is problematic because macroparameters such as cluster surface tension and vapor saturation pressure are not physically correct for small cluster sizes. In this work, we propose a kinetic based evaporation model obtained from unimolecular dissociation theory (UDT) to model argon cluster evaporation processes in a free expanding plume. The UDT argon cluster evaporation model has been directly verified by molecular dynamics (MD). It is found that although there is about one order of magnitude difference in the CNT and UDT evaporation rates, these two theories predict similar cluster evaporation rate trends as a function of cluster size and temperature. The verified new UDT evaporation model, as well as the previous CNT model, are applied to a free expanding argon condensation plume. The simulation results show that although there are some differences in cluster number density and average cluster size using the CNT and UDT evaporation models, the condensation onset conditions and Rayleigh scattering intensity for both models agree reasonably well with experimental data. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
8. Kinetic Nucleation Model for Free-Expanding Water Condensation Plume Simulations.
- Author
-
Zheng Li, Jiaqiang Zhong, Levin, Deborah A., and Garrison, Barbara J.
- Subjects
PHYSICS research ,NUCLEATION ,PHASE transitions ,CONDENSATION ,KINETIC theory of gases ,MONTE Carlo method - Abstract
The direct simulation Monte Carlo (DSMC), a kinetic method, was recently expanded to include the simulation of homogeneous condensation in the free expansion of water plumes and the results show that the nucleation rate is a key factor to accurately modeling of condensation phenomenon. In this work, we assumed the bimolecular formation as the main microscopic mechanisms of water dimer formation and the formation probabilities through collision between two water molecules for different collision energies were obtained by MD simulations and found to decrease with collision energy. The formation probabilities and post-collisional velocity and energy distributions were then integrated into DSMC simulations of a free expansion of an orifice condensation plume with different chamber stagnation temperatures. The dimer mole fraction increases with distance from the orifice and becomes constant after a distance of about two orifice diameters. The terminal dimer mole fraction was found to decrease with chamber stagnation temperatures but higher than experimentally observed. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
9. Modeling of CO2 Homogeneous Condensation Plumes.
- Author
-
Jiaqiang Zhong, Zheng Li, and Levin, Deborah A.
- Subjects
PHYSICS research ,CARBON dioxide ,CONDENSATION ,KINETIC theory of gases ,MONTE Carlo method - Abstract
A direct simulation Monte Carlo (DSMC) based homogenous condensation model is developed to study CO
2 free expanding condensation plumes. It is found that initial condensation onset locations are less sensitive to gas pressure or plume stagnation pressure than temperature. Gas translational and rotational temperatures are found to be in the equilibrium state for both condensation and noncondensation simulations. Numerical gas and cluster temperatures are compared to the experimental data, and the simulation results show that cluster temperatures are higher than gas temperatures due to condensation latent heat. The numerical simulation results of CO2 cluster size, number density, and gas mole fraction in homogenous condensation plume are compared with experimental data of Ramos et al. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
10. Extension of the DSMC method to high pressure flows.
- Author
-
Titov, Evgeny V. and Levin, Deborah A.
- Subjects
- *
SIMULATION methods & models , *MONTE Carlo method , *INVISCID flow , *NAVIER-Stokes equations , *ENSKOG equation , *TRANSPORT theory - Abstract
A collision-limiter method, designated as equilibrium direct simulation Monte Carlo (eDSMC), is proposed to extend the DSMC technique to high pressure flows. The method is similar to collision-limiter schemes considered in the past with the important distinction that for inviscid flows, equilibrium is enforced in the entire flow by providing a sufficient number of collisions, based on pre-simulation testing. To test the method with standard DSMC and Navier-Stokes (NS) methods, axi-symmetric nozzle and embedded-channel flows are simulated and compared with experimental temperature data and pre-existing calculations, respectively. The method is shown to agree with third-order Eulerian nozzle flows and first-order channel flows. Chapman-Enskog theory is utilized to predict the range of initial conditions where eDSMC is potentially useful for modeling flows that contain viscous boundary layer regions. Comparison with supersonic nozzle data suggests that the eDSMC method is not adequate for capturing the large variation in flow length scales occurring in supersonic expansions into a vacuum. However, when eDSMC is used in combination with the baseline-DSMC method a near-exact solution is obtained with a considerable computational savings compared to the exact DSMC solution. Viscous flow channel calculations are found to agree well with an exact Navier-Stokes (NS) calculation for a small Knudsen number case as predicted by Chapman-Enskog theory. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
11. Multi-scale thermal response modeling of an AVCOAT-like thermal protection material.
- Author
-
Sawant, Saurabh S., Rao, Pooja, Harpale, Abhilash, Chew, Huck Beng, and Levin, Deborah A.
- Subjects
- *
MICROSTRUCTURE , *ABLATION techniques , *MATERIALS , *HEAT transfer coefficient , *MONTE Carlo method - Abstract
Highlights • DSMC study of the effect of AVCOAT-like microstructure on internal gas transport. • Permeability and tortuosity computation for AVCOAT and comparison with fibrous TPS. • Coupled convection, conduction, and radiation using a random walk model. • Study of AVCOAT with spatially varying thermophysical properties at high temperatures. • Comparison of thermal response predicted by stochastic versus finite-volume approaches. Abstract A multi-scale modeling approach based on the stochastic Direct Simulation Monte Carlo (DSMC) and walker methods is developed to understand the complex flows and thermophysical phenomena through a syntactic foam TPS, similar to AVCOAT. Using novel, unstructured adaptive mesh refinement/Octree grids and newly developed subsonic boundary conditions, the counter-flow transport of boundary layer and pyrolysis gases through the porous microstructure is modeled for the first time. Permeability of the microstructure models having porosities of 0.71 and 0.86 is computed in the DSMC simulations and compared to a fibrous TPS material. The rigorous development of a stochastic based thermal response model that can couple convective, conductive, and radiative heat transfer through a porous material having non-uniform thermophysical properties and high temperature gradients is presented and compared with a one-dimensional finite-volume approach. The material thermal response is found to be dominated by conduction, yet, the interactions between boundary layer and pyrolysis species on the actual 3-D geometry, which cannot be considered in traditional material response solvers, may in fact cause them to underpredict the TPS material temperature. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
12. Application of adaptively refined unstructured grids in DSMC to shock wave simulations.
- Author
-
Sawant, Saurabh S., Tumuklu, Ozgur, Jambunathan, Revathi, and Levin, Deborah A.
- Subjects
- *
SHOCK waves , *HYPERSONIC flow , *MACH number , *HEAT flux , *SIMULATION methods & models - Abstract
An efficient, new DSMC framework based on AMR/octree unstructured grids is demonstrated for the modeling of near-continuum, strong shocks in hypersonic flows. The code is able to capture the different length scales in such flows through the use of a linearized representation of the unstructured grid using Morton-Z space filling curve for efficient access of collision cells. Strategies were developed to achieve a strong scaling of nearly ideal speed up to 4096 processors and 87% efficiency (weak scaling) for 8192 processors for a strong shock created by flow over a hemisphere. To achieve these very good scalings, algorithms were developed to weight the computational work of a processor by the use of profiled run time data, create maps to optimize processor point-to-point communications, and efficiently generate new DSMC particles every time step. Rigorous thermal non-equilibrium required for modeling high Mach number shocks was achieved through the accurate modeling of collision temperatures on a sampling grid designed to be compatible with the above approaches. The simulation of a nitrogen flow over a double wedge configuration for near-continuum conditions revealed complex hypersonic SWBLIs as well as three-dimensional gas-surface kinetic effects such as velocity and temperature slip. The simulations showed that three-dimensional effects are important in predicting the size of the separation bubble, which in turn, influences gas-surface measurements such as pressure and heat flux. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
13. Simulation of droplet heating and desolvation in inductively coupled plasma—part II: coalescence in the plasma
- Author
-
Benson, Craig M., Zhong, Jiaqiang, Gimelshein, Sergey F., Levin, Deborah A., and Montaser, Akbar
- Subjects
- *
MONTE Carlo method , *ARGON , *HEATING - Abstract
A numerical model is developed to consider for the first time droplet coalescence along with transport, heating and desolvation in an argon inductively coupled plasma (Ar ICP). The direct simulation Monte Carlo (DSMC) method and the Ashgriz–Poo model are used, respectively, to compute droplet–droplet interactions and to determine the outcome of droplet collisions. Molecular dynamics (MD) simulations support the use of the Ashgriz–Poo coalescence model for small droplet coalescence. Simulations predict spatial maps of droplet number and mass densities within an Ar ICP for a conventional nebulizer-spray chamber arrangement, a direct injection high efficiency nebulizer (DIHEN), and a large bore DIHEN (LB-DIHEN). The primary findings are: (1) even at 1500 W, the collisions of the droplets in the plasma lead primarily to coalescence, particularly for direct aerosol injection; (2) the importance of coalescence in a spray simulation exhibits a complex relationship with the gas temperature and droplet size; (3) DIHEN droplets penetrate further into the Ar ICP when coalescence is considered; and (4) droplets from a spray chamber or the LB-DIHEN coalesce less frequently than those from a DIHEN. The implications of these predictions in spectrochemical analysis in ICP spectrometry are discussed. [Copyright &y& Elsevier]
- Published
- 2003
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.