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- Adaptive control (1)
- Design optimization (1)
- Detonation tubes (1)
- Direct simulation Monte Carlo; velocity distribution functions; rarefied flows; non-equilibrium flows; visualization (1)
- Method of characteristic (1)
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- Optimization; turbine; turbomachinery; design (1)
- Predictor feedback (1)
- Pulse detonation engines (1)
- Rotating detonation combustor; heat flux; reduced model; pressure-gain combustion (1)
- Sliding mode control (1)
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- Supersonic internal flow; method of characteristics; intakes; turbomachinery; optimization (1)
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Articles 1 - 30 of 57
Full-Text Articles in Engineering
Turbine Passage Design Methodology To Minimize Entropy Production-A Two-Step Optimization Strategy, Paht Juangphanich, Cis De Maesschalck, Guillermo Paniagua
Turbine Passage Design Methodology To Minimize Entropy Production-A Two-Step Optimization Strategy, Paht Juangphanich, Cis De Maesschalck, Guillermo Paniagua
School of Aeronautics and Astronautics Faculty Publications
Rapid aerodynamic design and optimization is essential for the development of future turbomachinery. The objective of this work is to demonstrate a methodology from 1D mean-line-design to a full 3D aerodynamic optimization of the turbine stage using a parameterization strategy that requires few parameters. The methodology is tested by designing a highly loaded and efficient turbine for the Purdue Experimental Turbine Aerothermal Laboratory. This manuscript describes the entire design process including the 2D/3D parameterization strategy in detail. The objective of the design is to maximize the entropy definition of efficiency while simultaneously maximizing the stage loading. Optimal design trends are …
Numerical Assessment Of The Convective Heat Transfer In Rotating Detonation Combustors Using A Reduced-Order Model, James Braun, Jorge Sousa, Guillermo Paniagua
Numerical Assessment Of The Convective Heat Transfer In Rotating Detonation Combustors Using A Reduced-Order Model, James Braun, Jorge Sousa, Guillermo Paniagua
School of Aeronautics and Astronautics Faculty Publications
The pressure gain across a rotating detonation combustor offers an efficiency rise and potential architecture simplification of compact gas turbine engines. However, the combustor walls of the rotating detonation combustor are periodically swept by both detonation and oblique shock waves at several kilohertz, disrupting the boundary layer, resulting in a rather complex convective heat transfer between the fluid and the solid walls. A computationally fast procedure is presented to calculate this extraordinary convective heat flux along the detonation combustor. First, a numerical model combining a two-dimensional method of characteristics approach with a monodimensional reaction model is used to compute the …
Prediction-Based Adaptive Robust Control For A Class Of Uncertain Time-Delay Systems, Jayaprakash Suraj Nandiganahalli, Cheolhyeon Kwon, Inseok Hwang
Prediction-Based Adaptive Robust Control For A Class Of Uncertain Time-Delay Systems, Jayaprakash Suraj Nandiganahalli, Cheolhyeon Kwon, Inseok Hwang
School of Aeronautics and Astronautics Faculty Publications
This paper presents an integrated control design approach for a class of dynamical systems that satisfy a certain matching condition subject to known input time-delay, unknown parameters, and time-varying disturbances, simultaneously. A novel nonlinear predictor adaptive robust control (PARC) is proposed to track a desired state trajectory. The controller uses predictor-based model compensation to attenuate the effect of input time-delay, gradient type projection with prediction-based learning mechanisms to reduce the parameter uncertainties, and prediction-based nonlinear robust feedback to attenuate the effect of model approximation errors and disturbances, simultaneously. The controller guarantees a prescribed transient performance (with global exponential convergence) and …
Multi-Stage Nozzle-Shape Optimization For Pulsed Hydrogen-Air Detonation Combustor, Francesco Ornano, James Braun, Bayindir H. Saracoglu, Guillermo Paniagua
Multi-Stage Nozzle-Shape Optimization For Pulsed Hydrogen-Air Detonation Combustor, Francesco Ornano, James Braun, Bayindir H. Saracoglu, Guillermo Paniagua
School of Aeronautics and Astronautics Faculty Publications
hermal engines based on pressure gain combustion offer new opportunities to generate thrust with enhanced efficiency and relatively simple machinery. The sudden expansion of detonation products from a single-opening tube yields thrust, although this is suboptimal. In this article, we present the complete design optimization strategy for nozzles exposed to detonation pulses, combining unsteady Reynolds-averaged Navier-Stokes solvers with the accurate modeling of the combustion process. The parameterized shape of the nozzle is optimized using a differential evolution algorithm to maxi mize the force at the nozzle exhaust. The design of experiments begins with a first optimization considering steady-flow conditions, subsequently …
Entropy Minimization Design Approach Of Supersonic Internal Passages, Jorge Sousa, Guillermo Paniagua
Entropy Minimization Design Approach Of Supersonic Internal Passages, Jorge Sousa, Guillermo Paniagua
School of Aeronautics and Astronautics Faculty Publications
Fluid machinery operating in the supersonic regime unveil avenues towards more compact technology. However, internal supersonic flows are associated with high aerodynamic and thermal penalties, which usually prevent their practical implementation. Indeed, both shock losses and the limited operational range represent particular challenges to aerodynamic designers that should be taken into account at the initial phase of the design process. This paper presents a design methodology for supersonic passages based on direct evaluations of the velocity field using the method of characteristics and computation of entropy generation across shock waves. This meshless function evaluation tool is then coupled to an …
Effect Of Intermolecular Potential On Compressible Couette Flow In Slip And Transitional Regimes, Andrew B. Weaver, A Venkattraman, Alina A. Alexeenko
Effect Of Intermolecular Potential On Compressible Couette Flow In Slip And Transitional Regimes, Andrew B. Weaver, A Venkattraman, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
The effect of intermolecular potentials on compressible, planar flow in slip and transitional regimes is investigated using the direct simulation Monte Carlo method. Two intermolecular interaction models, the variable hard sphere (VHS) and the Lennard-Jones (LJ) models, are first compared for subsonic and supersonic Couette flows of argon at temperatures of 40, 273, and 1,000 K, and then for Couette flows in the transitional regime ranging from Knudsen numbers (Kn) of 0.0051 to 1. The binary scattering model for elastic scattering using the Lennard-Jones (LJ) intermolecular potential proposed recently [A. Venkattraman and A. Alexeenko, “Binary scattering model for Lennard-Jones potential: …
Kinetic Modeling Of Evolution Of 3 + 1:Resonance Enhanced Multiphoton Ionization Plasma In Argon At Low Pressures, Siva Sashank Tholeti, Mikhail N. Shneider, Alina A. Alexeenko
Kinetic Modeling Of Evolution Of 3 + 1:Resonance Enhanced Multiphoton Ionization Plasma In Argon At Low Pressures, Siva Sashank Tholeti, Mikhail N. Shneider, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
We present numerical kinetic modeling of generation and evolution of the plasma produced as a result of resonance enhanced multiphoton ionization (REMPI) in Argon gas. The particle-in-cell/Monte Carlo collision (PIC/MCC) simulations capture non-equilibrium effects in REMPI plasma expansion by considering the major collisional processes at the microscopic level: elastic scattering, electron impact ionization, ion charge exchange, and recombination and quenching for metastable excited atoms. The conditions in one-dimensional (1D) and two-dimensional (2D) formulations correspond to known experiments in Argon at a pressure of 5 Torr. The 1D PIC/MCC calculations are compared with the published results of local drift-diffusion model, obtained …
Experimental Measurements And Modeling Of Convective Heat Transfer In The Transitional Rarefied Regime, Andrew D. Strongrich, Alina A. Alexeenko
Experimental Measurements And Modeling Of Convective Heat Transfer In The Transitional Rarefied Regime, Andrew D. Strongrich, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
We present experimental measurements and numerical simulations of convective heat transferperformance in the transitional rarefied regime for an isolated rectangular beam geometry. Experiments were performed using single crystalline silicon beam elements having width-to-thickness aspect ratios of 8.5 and 17.4. Devices were enclosed in a vacuum chamber and heated resistively using a DC power supply. A range of pressures corresponding to Knudsen numbers between 0.096 and 43.2 in terms of device thickness were swept, adjusting applied power to maintain a constant temperature of 50 K above the ambient temperature. Both parasiticelectrical resistance associated with the hardware and radiative exchange with the …
Effect Of Molecular Models On Viscosity And Thermal Conductivity Calculations, Andrew B. Weaver, Alina A. Alexeenko
Effect Of Molecular Models On Viscosity And Thermal Conductivity Calculations, Andrew B. Weaver, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
The effect of molecular models on viscosity and thermal conductivity calculations is investigated. The Direct Simulation Monte Carlo (DSMC) method for rarefied gas flows is used to simulateCouette and Fourier flows as a means of obtaining the transport coefficients. Experimentalmeasurements for argon (Ar) provide a baseline for comparison over a wide temperature range of 100–1,500 K. The variable hard sphere (VHS), variable soft sphere (VSS), and Lennard-Jones (L-J) molecular models have been implemented into a parallel version of Bird’s one-dimensional DSMC code, DSMC1, and the model parameters have been recalibrated to the current experimental data set. While the VHS and …
Amplification And Reversal Of Knudsen Force By Thermoelectric Heating, William J. O'Neill, Mizuki Wada, Andrew D. Strongrich, Anthony Cofer, Alina A. Alexeenko
Amplification And Reversal Of Knudsen Force By Thermoelectric Heating, William J. O'Neill, Mizuki Wada, Andrew D. Strongrich, Anthony Cofer, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
We show that the Knudsen thermal force generated by a thermally-induced flow over a heated beam near a colder wall could be amplified significantly by thermoelectric heating. Bidirectional actuation is achieved by switching the polarity of the thermoelectric device bias voltage. The measurements of the resulting thermal forces at different rarefaction regimes, realized by changing geometry and gas pressure, are done using torsional microbalance. The repulsive or attractive forces between a thermoelectrically heated or cooled plate and a substrate are shown to be up to an order of magnitude larger than for previously studied configurations and heating methods due to …
Frequency Response Of Atmospheric Pressure Gas Breakdown In Micro/Nanogaps, Abbas Semnani, Ayyaswamy Venkattraman, Alina A. Alexeenko, Dimitrios Peroulis
Frequency Response Of Atmospheric Pressure Gas Breakdown In Micro/Nanogaps, Abbas Semnani, Ayyaswamy Venkattraman, Alina A. Alexeenko, Dimitrios Peroulis
School of Aeronautics and Astronautics Faculty Publications
In this paper, we study gas breakdown in micro/nanogaps at atmospheric pressure from low RF to high millimeter band. For gaps larger than about 10 lm, the breakdown voltage agrees with macroscale vacuum experiments, exhibiting a sharp decrease at a critical frequency, due to transition between the boundary- and diffusion-controlled regimes, and a gradual increase at very high frequencies as a result of inefficient energy transfer by field. For sub-micron gaps, a much lower breakdown is obtained almost independent of frequency because of the dominance of field emission
Pre-Breakdown Evaluation Of Gas Discharge Mechanisms In Microgaps, Abbas Semnani, Ayyaswamy Venkattraman, Alina A. Alexeenko, Dimitrios Peroulis
Pre-Breakdown Evaluation Of Gas Discharge Mechanisms In Microgaps, Abbas Semnani, Ayyaswamy Venkattraman, Alina A. Alexeenko, Dimitrios Peroulis
School of Aeronautics and Astronautics Faculty Publications
The individual contributions of various gas discharge mechanisms to total pre-breakdown current in microgaps are quantified numerically. The variation of contributions of field emission and secondary electron emission with increasing electric field shows contrasting behavior even for a given gap size. The total current near breakdown decreases rapidly with gap size indicating that microscale discharges operate in a high-current, low-voltage regime. This study provides the first such analysis of breakdown mechanisms and aids in the formulation of physics-based theories for microscale breakdown
Nonlinear Effects In Squeeze Film Gas Damping On Microbeams, S Chigullapalli, A Weaver, Alina A. Alexeenko
Nonlinear Effects In Squeeze Film Gas Damping On Microbeams, S Chigullapalli, A Weaver, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
We consider squeeze film gas damping during microbeam motion away and toward a substrate as occurs during opening and closing of RF switches and other MEMS devices. The numerical solution of the gas damping problem in two-dimensional geometries is obtained based on the Boltzmann-ESBGK equation. The difference in damping force between downward and upward moving beams is shown to vary from as little from as 5% for low beam velocities of 0.1m/s to more than 200% at 2.4m/s. For a constant velocity magnitude of 0.8m/s, this difference increases from 60% to almost 90% when the pressure is reduced by an …
A Study Of Field Emission Process In Electrostatically Actuated Mems Switches, L Michalas, A Garg, A Venkattraman, M Koutsoureli, Alina A. Alexeenko, Dimitrios Peroulis, G Papaioannou
A Study Of Field Emission Process In Electrostatically Actuated Mems Switches, L Michalas, A Garg, A Venkattraman, M Koutsoureli, Alina A. Alexeenko, Dimitrios Peroulis, G Papaioannou
School of Aeronautics and Astronautics Faculty Publications
A study of field emission process in MEMS-based capacitor/switch-like geometries is presented. High resolution current-voltage characteristics up to breakdown have been obtained across micro-gaps in fixed-fixed Metal-Air- Metal and Metal-Air-Insulator-Metal structures. In metallic devices the I-V dependence reveals Fowler –Nordheim theory effects. In the presence of insulator the process is found to be limited by the film conductivity following Poole –Frenkel dependence. The data analysis reveals the major importance of surface asperities on the onset of the field emission process while it is also presented that charge transfer may occur between metal and insulator surfaces even in the presence of …
Scaling Law For Direct Current Field Emission-Driven Microscale Gas Breakdown, A Venkattraman, Alina A. Alexeenko
Scaling Law For Direct Current Field Emission-Driven Microscale Gas Breakdown, A Venkattraman, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
The effects of field emission on direct current breakdown in microscale gaps filled with an ambient neutral gas are studied numerically and analytically. Fundamental numerical experiments using the particle-in-cell/Monte Carlo collisions method are used to systematically quantify microscale ionization and space-charge enhancement of field emission. The numerical experiments are then used to validate a scaling law for the modified Paschen curve that bridges field emission-driven breakdown with the macroscale Paschen law. Analytical expressions are derived for the increase in cathode electric field, total steady state current density, and the ion-enhancement coefficient including a new breakdown criterion. It also includes the …
Assessment Of High-Enthalpy Air Chemistry Models For Hypervelocity Ground-Based Experiments, Marat Kulakhmetov, Yevgeniy A. Bondar, Mikhail S. Ivanov, Alina A. Alexeenko
Assessment Of High-Enthalpy Air Chemistry Models For Hypervelocity Ground-Based Experiments, Marat Kulakhmetov, Yevgeniy A. Bondar, Mikhail S. Ivanov, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
Hypersonic vehicles re-entering Earth's atmosphere with orbital velocities generate gas flows with significant thermo-chemical non-equilibrium. Detailed kinetics of chemical reactions at such conditions is still not well understood but it may affect vehicle's thermal loads, aerodynamic moments and thermal radiation. This work assesses the Total Collision Energy (TCE) and the Kuznetsov-based state specific (KSS) chemical reaction models at pressures between 1 and 50 torr and velocities between 4 and 10 km/s in order to identify best test conditions for validating the models. Hypersonic flows at such conditions can be studied at the hypervelocity impact range facilities.
A Comparative Study Of No-Time-Counter And Majorant Collision Frequency Numerical Schemes In Dsmc, A Venkattraman, Alina A. Alexeenko, M A. Gallis, M S. Ivanov
A Comparative Study Of No-Time-Counter And Majorant Collision Frequency Numerical Schemes In Dsmc, A Venkattraman, Alina A. Alexeenko, M A. Gallis, M S. Ivanov
School of Aeronautics and Astronautics Faculty Publications
The direct simulation Monte Carlo (DSMC) method is a stochastic approach to solve the Boltzmann equation and is built on various numerical schemes for transport, collision and sampling. This work aims to compare and contrast two popular O(N) DSMC collision schemes - no-time-counter (NTC) and majorant collision frequency (MCF) - with the goal of identifying the fundamental differences. MCF and NTC schemes are used in DSMC simulations of a spatially homogeneous equilibrium gas to study convergence with respect to various collision parameters. While the MCF scheme forces the reproduction of the exponential distribution of time between collisions, …
Climatic Effects Of The Chicxulub Impact Ejecta, Devon Parkos, Marat Kulakhmetov, Brandon Johnson, Henry J. Melosh, Alina A. Alexeenko
Climatic Effects Of The Chicxulub Impact Ejecta, Devon Parkos, Marat Kulakhmetov, Brandon Johnson, Henry J. Melosh, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
Examining the short and long term effects of the Chicxulub impact is critical for understanding how life developed on Earth. While the aftermath of the initial impact would have produced harmful levels of radiation sufficient for eradicating a large portion of terrestrial life, this process does not explain the concurrent marine extinction. Following the primary impact, a large quantity of smaller spherules would de-orbit and re-enter the earths atmosphere, dispersed nearly uniformly across the planet. This secondary wave of debris would re-enter at high velocities, altering the chemical composition of the atmosphere. Furthermore, the combined surface area for the spherules …
Binary Scattering Model For Lennard-Jones Potential: Transport Coefficients And Collision Integrals For Non-Equilibrium Gas Flow Simulations, Ayyaswamy Venkattraman, Alina A. Alexeenko
Binary Scattering Model For Lennard-Jones Potential: Transport Coefficients And Collision Integrals For Non-Equilibrium Gas Flow Simulations, Ayyaswamy Venkattraman, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
A Lennard-Jones (LJ) binary interaction model for dilute gases is obtained by representing the exact scattering angle as a polynomial expansion in non-dimensional collision variables. Rigorous theoretical verification of the model is performed by comparison with exact values of diffusion and viscosity cross sections and related collision integrals. The collision quantities given by the polynomial approximation model agree within 3.5% with those of the exact LJ scattering. The proposed model is compared in detail with the generalized soft sphere (GSS) model which is the closest in terms of fidelity among existing direct simulation Monte Carlo collision models. The GSS model's …
A Runge-Kutta Discontinuous Galerkin Solver For 2d Boltzmann Model Equations: Verification And Analysis Of Computational Performance, Wei Su, Alina A. Alexeenko, Guobiao Cai
A Runge-Kutta Discontinuous Galerkin Solver For 2d Boltzmann Model Equations: Verification And Analysis Of Computational Performance, Wei Su, Alina A. Alexeenko, Guobiao Cai
School of Aeronautics and Astronautics Faculty Publications
The high-order Runge-Kutta discontinuous Galerkin (DG) method is extended to the 2D kinetic model equations describing rarefied gas flows. A DG-type discretization of the equilibrium velocity distributions is formulated for the Bhatnagar-Gross-Krook and ellipsoidal statistical models which enforce a weak conservation of mass, momentum and energy in the collision relaxation term. The RKDG solutions have up to 3rd-order spatial accuracy and up to 4th-order time accuracy. Verification is carried out for a steady 1D Couette flow and a 2D thermal conduction problem by comparison with DSMC and analytical solutions. The computational performance of the RKDG method …
Direct Measurements And Numerical Simulations Of Gas Charging In Microelectromechanical System Capacitive Switches, A Venkattraman, A Garg, D Peroulis, Alina A. Alexeenko
Direct Measurements And Numerical Simulations Of Gas Charging In Microelectromechanical System Capacitive Switches, A Venkattraman, A Garg, D Peroulis, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
Gas breakdown in microelectromechanical system capacitive switches is demonstrated using high resolution current measurements and by particle-in-cell/Monte Carlo collision (PIC/MCC) simulations. Measurements show an electric current through a 3 μm air gap increasing exponentially with voltage, starting at 60 V. PIC/MCC simulations with Fowler-Nordheim [Proc. R. Soc. London, Ser. A 119, 173 (1928)] field emission reveal self-sustained discharges with significant ion enhancement and a positive space charge. The effective ion-enhanced field emission coefficient increases with voltage up to about 0.3 with an electron avalanche occurring at 159 V. The measurements and simulations demonstrate a charging mechanism for microswitches …
Immersed Boundary Method For Boltzmann Model Kinetic Equations, Cem Pekardan, Sruti Chigullapalli, Alina A. Alexeenko
Immersed Boundary Method For Boltzmann Model Kinetic Equations, Cem Pekardan, Sruti Chigullapalli, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
Three different immersed boundary method formulations are presented for Boltzmann model kinetic equations such as Bhatnagar-Gross-Krook (BGK) and Ellipsoidal statistical Bhatnagar-Gross-Krook (ESBGK) model equations. 1D unsteady IBM solution for a moving piston is compared with the DSMC results and 2D quasi-steady microscale gas damping solutions are verified by a conformal finite volume method solver. Transient analysis for a sinusoidally moving beam is also carried out for the different pressure conditions (1 atm, 0.1 atm and 0.01 atm) corresponding to Kn=0.05,0.5 and 5. Interrelaxation method (Method 2) is shown to provide a faster convergence as compared to the traditional interpolation scheme …
Unsteady 3d Rarefied Flow Solver Based On Boltzmann-Esbgk Model Kinetic Equations, Sruti Chigullapalli, Alina A. Alexeenko
Unsteady 3d Rarefied Flow Solver Based On Boltzmann-Esbgk Model Kinetic Equations, Sruti Chigullapalli, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
Formulation and verification of unsteady rarefied flow solver based on BoltzmannESBGK equations in arbitrary three-dimensional geometries is presented. The solver is based on the finite volume method in physical space and the discrete ordinate method in velocity space with an implicit time discretization. Verification is carried out for an unsteady approach to equilibrium, a steady one-dimensional Couette flow and a two-dimensional quasi-steady gas damping problem. Finally, the application of the full 3D parallel solver is considered to simulate unsteady microscale gas damping in a micro-electro-mechanical system switch.
Focused Solar Ablation: A Nanosat-Based Method For Active Removal Of Space Debris, Alina A. Alexeenko, A Venkattraman
Focused Solar Ablation: A Nanosat-Based Method For Active Removal Of Space Debris, Alina A. Alexeenko, A Venkattraman
School of Aeronautics and Astronautics Faculty Publications
A novel concept for the active removal of space debris using solar power is proposed. Focused solar ablation is an in-space propulsion concept based on using concentrator mirrors on nanosats and using the solar power to evaporate material from the debris to produce deceleration thrust thereby providing the ∆V necessary to deorbit. An energy balance is used along with free-molecular effusion theory to estimate the thrust produced by the concept and the corresponding deorbit times for an aluminum debris masses of 10 kg and 0.27 kg for various concentrator mirror areas and the diameter of the spot on which the …
Microspike Based Chemical/Electric Thruster Concept For Versatile Nanosat Propulsion, Anthony Cofer, A Venkattraman, Alina A. Alexeenko
Microspike Based Chemical/Electric Thruster Concept For Versatile Nanosat Propulsion, Anthony Cofer, A Venkattraman, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
Small spacecraft that can be categorized as microsats, nanosats, and picosats has a strong potential for wide applications in communication, scientific experiments, and space exploration. In order to combine the advantages of both electric and chemical propulsion thrusters, a dual-mode microspike based thruster concept is proposed. For a fixed input power, it can operate in either a high-Isp mode or a high-thrust mode depending on the propulsive maneuver requirements. The hybrid thruster consists of a plug-annular cold or heated gas thruster in the chemical mode and a field emission thruster housed within the plug operating in the electric mode using …
Dsmc Collision Model For The Lennard-Jones Potential: Efficient Algorithm And Verification, A Venkattraman, Alina A. Alexeenko
Dsmc Collision Model For The Lennard-Jones Potential: Efficient Algorithm And Verification, A Venkattraman, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
An efficient algorithm to implement elastic scattering using the Lennard-Jones (LJ) intermolecular potential in the direct simulation Monte Carlo (DSMC) method is presented. The exact elastic scattering angle for the LJ intermolecular potential obtained by numerical integration is used to construct a piecewise polynomial representation in terms of two collision parameters - the reduced impact parameter and the reduced relative energy. The 5 thdegree polynomials representation is obtained using the Chebyshev basis. The implementation valid for reduced relative energies ranging from 0.001 to 10.0 is verified by DSMC simulations of subsonic and supersonic Couette flow of Argon at temperatures of …
Effects Of Uncertainty In Gas-Surface Interaction On Dsmc Simulations Of Hypersonic Flows, Marat Kulakhmetov, A Venkattraman, Alina A. Alexeenko
Effects Of Uncertainty In Gas-Surface Interaction On Dsmc Simulations Of Hypersonic Flows, Marat Kulakhmetov, A Venkattraman, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
This study uses the non-intrusive generalized polynomial chaos method to investigate the effects of uncertainties in the gas-surface interaction model on the hypersonic boundary layer flow over a flat plate. In particular, the polynomial chaos method is applied to assess uncertainties in the surface shea, normal stress, heat flux, flowfield temperature and accomodation coefficient. The polynomial chaos approach allows us to estimate probability density functions from fewer flowfield samples than the traditional random Monte Carlo sampling. The flowfield solutions are computed by the DSMC code SMILE. The analysis shows that surface fluxes and flowfields in the hypersonic boundary layer are …
Simulations Of Vapor/Ice Dynamics In A Freeze-Dryer Condenser, Arnab Ganguly, A Venkattraman, Alina A. Alexeenko
Simulations Of Vapor/Ice Dynamics In A Freeze-Dryer Condenser, Arnab Ganguly, A Venkattraman, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
Freeze-drying is a low-pressure, low-temperature condensation pumping process widely used in the manufacture of pharmaceuticals for removal of solvents by sublimation. Key performance characteristics of a freeze-dryer condenser are largely dependent on the vapor and ice dynamics in the low-pressure environment. The main objective of this work is to develop a modeling and computational framework for analysis of vapor and ice dynamics in such freeze-dryer condensers. The direct Simulation Monte Carlow (DSMC) technique is applied to model the relevant physical processes that accompany the vapor flow in the condenser chamber. Low-temperature water vapor molecular model is applied in the DSMC …
Visualizing Non-Equilibrium Flow Simulations Using 3-D Velocity Distribution Functions, A Venkattraman, Alina A. Alexeenko
Visualizing Non-Equilibrium Flow Simulations Using 3-D Velocity Distribution Functions, A Venkattraman, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
Scientific visualization techniques have been used to probe and understand better the physics of non-equilibrium flows. A visualization methodology for nonequilibrium flow simulations using 3-D velocity distribution functions (VDFs) is illustrated in application to various non-equilibrium flow problems. A one-dimensional normal shock wave problem is considered for two different upstream Mach numbers corresponding to weak and strong non-equilibrium flow conditions. The iso-surfaces of 3-D VDFs inside the shock wave obtainedusing various solution techniques including the ES-BGK method, DSMC technique, Mott-Smith solution, and the Navier-Stokes (NS) distribution functions using Chapman-Enskog theory are compared and contrasted. The visualization technique is extended to …
Direct Simulation Monte Carlo Study Of Effects Of Thermal Nonuniformities In Electron-Beam Physical Vapor Deposition, A Venkattraman, Alina A. Alexeenko
Direct Simulation Monte Carlo Study Of Effects Of Thermal Nonuniformities In Electron-Beam Physical Vapor Deposition, A Venkattraman, Alina A. Alexeenko
School of Aeronautics and Astronautics Faculty Publications
In a typical electron-beam physical vapor deposition system, there is limited control over how the high-power electron beam heats the metal surface. This leads to thermal nonuniformities at the melt. Three-dimensional direct simulation Monte Carlo simulations were performed with the aim of quantifying the effect of such spatial variations of source temperature in thin film depositions using an electron-beam physical vapor deposition system. The source temperature distribution from a typical deposition process was used in the direct simulation Monte Carlo simulations performed for various mass flow rates. The use of an area-averaged temperature is insufficient for all mass flow rates …