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Graham V. Candler - One of the best experts on this subject based on the ideXlab platform.
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rate effects in Hypersonic Flows
Annual Review of Fluid Mechanics, 2019Co-Authors: Graham V. CandlerAbstract:Hypersonic Flows are energetic and result in regions of high temperature, causing internal energy excitation, chemical reactions, ionization, and gas-surface interactions. At typical flight conditi...
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Rate Effects in Hypersonic Flows
Annual Review of Fluid Mechanics, 2019Co-Authors: Graham V. CandlerAbstract:Hypersonic Flows are energetic and result in regions of high temperature, causing internal energy excitation, chemical reactions, ionization, and gas-surface interactions. At typical flight conditions, the rates of these processes are often similar to the rate of fluid motion. Thus, the gas state is out of local thermodynamic equilibrium and must be described by conservation equations for the internal energy and chemical state. Examples illustrate how competition between rates in Hypersonic Flows can affect aerodynamic performance, convective heating, boundary layer transition, and ablation. The conservation equations are outlined, and the most widely used models for internal energy relaxation, reaction rates, and transport properties are reviewed. Gas-surface boundary conditions are described, including finite-rate catalysis and slip effects. Recent progress in the use of first-principles calculations to understand and quantify critical gas-phase reactions is discussed. An advanced finite-rate carbon ablation model is introduced and is used to illustrate the role of rate processes at Hypersonic conditions.
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advances in computational fluid dynamics methods for Hypersonic Flows
Journal of Spacecraft and Rockets, 2015Co-Authors: Graham V. Candler, Pramod K Subbareddy, Joseph M BrockAbstract:Over the past two decades or so, there have been many advances in the numerical simulation of Hypersonic Flows, with most effort focused on the development of upwind methods to produce accurate heat transfer rates for steady-state laminar and turbulent Flows. With parallelizable implicit methods, it is now possible to obtain full-vehicle solutions at reasonable computational cost. This paper reviews several of the most widely used approaches and discusses how the methods have been tuned to control numerical errors for strongly shocked Flows. The paper also discusses recent methods from the incompressible turbulence simulation literature that have been adapted to compressible Flows. These methods have dramatically lower levels of numerical dissipation and have been extended to high-order accuracy on smoothly varying hexahedral grids. The increased accuracy of these methods enables the solution of complex physics unsteady Hypersonic Flows.
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rate dependent energetic processes in Hypersonic Flows
Progress in Aerospace Sciences, 2015Co-Authors: Graham V. CandlerAbstract:Abstract In celebration of the first 60 years of the Air Force Office of Scientific Research, several studies of Hypersonic Flows dominated by rate-dependent energetic processes are revisited. The work presented shows the evolution and advancement of computational capabilities in this area, and illustrates some key lessons learned over the previous decade or so. Early work with Leyva and Hornung in the California Institute of Technology T5 Free-Piston Shock Tunnel had the goal of validating thermochemical models for high-enthalpy Flows. Several of these Flows are re-analyzed with more advanced numerical methods, resulting in improved comparisons with the experimental measurements. This work was followed by a series of experiments in the Calspan-University at Buffalo Research Center (now CUBRC Inc.) facilities at lower enthalpy conditions. Initial comparisons were poor, but with a better understanding of the facility behavior and the inclusion of key finite-rate processes, excellent agreement was obtained for nitrogen Flows. An interesting study related to plasmadynamics and finite-rate processes in a different type of flow is discussed. Finally, it is shown that recent advances in numerical methods that are beginning to enable the direct numerical simulation of key rate-dependent energetic processes in Hypersonic Flows.
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rate dependent energetic processes in Hypersonic Flows
43rd AIAA Fluid Dynamics Conference, 2013Co-Authors: Graham V. CandlerAbstract:In celebration of the first 60 years of the Air Force Office of Scientific Research, we revisit several studies of Hypersonic Flows dominated by rate-dependent energetic processes. The work presented shows the evolution and advancement of computational capabilities in this area, and illustrates some key lessons learned over the previous decade or so. We discuss some early work with Leyva and Hornung in the California Institute of Technology T5 Free-Piston Shock Tunnel that had the goal of validating thermochemical models for highenthalpy Flows. We re-analyze several of these Flows with more advanced numerical methods and find improved comparison with the experimental measurements. This work then lead to a series of experiments in the Calspan-University at Buffalo Research Center (now CUBRC Inc.) facilities at lower enthalpy. Initial comparisons were rather uninspiring, but with a better understanding of the facility behavior and the inclusion of key finite-rate processes, excellent agreement was obtained for nitrogen Flows. New experiments at CUBRC in a large expansion tunnel will likely shed further light several remaining puzzles related to these Flows. We also revisit an interesting study related to plasmadynamics and finite-rate processes in a different type of flow. Finally, we illustrate recent advances in numerical methods that are enabling the direct numerical simulation of key rate-dependent energetic processes in Hypersonic Flows.
Ganesh Natarajan - One of the best experts on this subject based on the ideXlab platform.
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shock wave boundary layer interactions in Hypersonic Flows
International Journal of Heat and Mass Transfer, 2014Co-Authors: Bibin John, Vinayak Kulkarni, Ganesh NatarajanAbstract:Abstract Shock-wave boundary layer interaction (SWBLI) and associated changes in wall properties for ramp induced flow breakdown have been considered in the present studies. A two dimensional finite volume based CFD solver has been developed and implemented successfully to study the SWBLI. Pressure measurements are invariantly considered in the literature for qualitative prediction of various SWBLI parameters. Hence efforts are made herewith to understand the laminar boundary layer separation in the presence of ramp induced shock wave through surface heat transfer rates, wall skin friction coefficient and wall pressure distributions. Effect of variation of freestream and wall properties along with geometric changes is considered in present studies. It has been observed from present limited investigations that ratio of wall temperature to freestream stagnation temperature is the governing parameter for SWBLI instead of the individual temperatures. Increase in Mach number is found to suppress the upstream influence which results in decrease in extent of separation. Efforts are also made to study the effect of leading edge bluntness on the SWBLI. These studies are found useful to confirm the earlier reported experimental observations regarding turbulent re-attachment.
Iain D Boyd - One of the best experts on this subject based on the ideXlab platform.
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open source direct simulation monte carlo chemistry modeling for Hypersonic Flows
AIAA Journal, 2015Co-Authors: T J Scanlon, Iain D Boyd, Craig White, Matthew K Borg, Rodrigo C Palharini, Erin D Farbar, Jason M Reese, Richard E BrownAbstract:An open-source implementation of chemistry modeling for the direct simulation Monte Carlo method is presented. Following the recent work of Bird (BirdG. A., “The Q-K Model for Gas Phase Chemical Reaction Rates,” Physics of Fluids, Vol. 23, No. 10, 2011, Paper 106101), an approach known as the quantum-kinetic method has been adopted to describe chemical reactions in a five-species air model using direct simulation Monte Carlo procedures based on microscopic gas information. The quantum-kinetic technique has been implemented within the framework of the dsmcFoam code, a derivative of the open-source computational-fluid-dynamics code OpenFOAM. Results for vibrational relaxation, dissociation, and exchange reaction rates for an adiabatic bath demonstrate the success of the quantum-kinetic model implementation in dsmcFoam when compared with analytical solutions for both inert and reacting conditions. A comparison is also made between the quantum-kinetic and total collision energy chemistry approaches for a hype...
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computation of Hypersonic Flows using the direct simulation monte carlo method
Journal of Spacecraft and Rockets, 2015Co-Authors: Iain D BoydAbstract:The direct simulation Monte Carlo method has evolved over 50 years into a powerful numerical technique for the computation of complex, nonequilibrium gas Flows. In this context, “nonequilibrium” means that the velocity distribution function is not in an equilibrium form due to a low number of intermolecular collisions within a fluid element. In Hypersonic flow, nonequilibrium conditions occur at high altitude and in regions of flowfields with small length scales. In this paper, the theoretical basis of the direct simulation Monte Carlo technique is discussed. In addition, the methods used in direct simulation Monte Carlo are described for simulation of high-temperature, real gas effects and gas–surface interactions. Several examples of the application of direct simulation Monte Carlo to Flows around blunt Hypersonic vehicles are presented to illustrate current capabilities. Areas are highlighted where further research on the direct simulation Monte Carlo technique is required.
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Computation of Hypersonic Flows Using the Direct Simulation Monte Carlo Method
Journal of Spacecraft and Rockets, 2014Co-Authors: Iain D BoydAbstract:The direct simulation Monte Carlo method (DSMC) has evolved over 50 years into a powerful numerical technique for the computation of complex, nonequilibrium gas Flows. In this context, nonequilibrium means that the velocity distribution function is not in an equilibrium form due to a low number of intermolecular collisions within a fluid element. In Hypersonic flow, nonequilibrium conditions occur at high altitude and in regions of flow fields with small length scales. In this article, the theoretical basis of the DSMC technique is discussed. In addition, the methods used in DSMC are described for simulation of high temperature, real gas effects and gas-surface interactions. Several examples of the application of DSMC to Flows around blunt Hypersonic vehicles are presented to illustrate current capabilities.
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modeling of electron energy phenomena in Hypersonic Flows
Journal of Thermophysics and Heat Transfer, 2012Co-Authors: Ali Gulhan, Iain D BoydAbstract:b0 = scattering parameter for 90 deg, Ze = 12 "0kTe , m CV;e = electron specific heat capacity, 3=2 R=Me , J= kg K cs = species charge Ds = species diffusion coefficients, m =s Ee = electron energy, e Cv;eTe 1=2 u v w Ei;f = first ionization energy per unit mass, J=kg Erot = rotational energy Evib = vibrational energy e = elementary charge, 1:6022 10 19 C ee = electron energy per unit mass of electrons, CV;eTe 1=2 u v w ee = modified electron energy per unit mass, e= ee evib;s = vibrational energy per unit mass F = inviscid flux vector H = total enthalpy per unit mass, J=kg Je = electron diffusion flux k = Boltzmann constant, 1:38065 10 23 m kg s 2 K 1 k v 0;j = vibrational-excitation rate coefficient from vibrational state 0 to j, m=s Ms = molecular weight of species s ms = species mass, kg n = unit vector normal to computational cell face ne = electron number density, m 3 pe = electron pressure, Pa Q = vector of conserved variables qe = electron heat flux R = universal gas constant, 8314.3, J=kg mole K Schem;e = electron energy gained by the electrons generated from chemical reactions Se = source term Se;modified = modified source term of the electron energy equation that includes the electron pressure term Sepg = approximation of the work done on electrons by the electric field induced by the electron pressure gradient Sinelastic;e = rate of inelastic energy exchange between electrons and molecules Strans e = energy exchange between translational and electron energies Te = electron temperature, K Ttrans = translational temperature, K Ttr = translational-rotational temperature, K Tve = vibrational-electron-electronic temperature, K U = velocity component normal to computational cell face u = flow velocity Ys = species mass fraction v;s = species characteristic vibrational temperature = thermal conductivity, K W=m D = Debye length, m = viscosity coefficient, N s =m s = species density, kg=m 3 es = collision cross section for electron and s species, m e = electron viscous stress es = electron-vibrational relaxation time, s _ !e = electron-mass production rate by chemical reactions, kg=m s "0 = vacuum permittivity, 8:854 10 , C V 1 m 1
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dissociation modeling in low density Hypersonic Flows of air
Physics of Fluids, 1995Co-Authors: Iain D Boyd, Graham V. Candler, Deborah A LevinAbstract:Vibration–dissociation coupling in low‐density, Hypersonic Flows of air is investigated. Radiative emission data for nitric oxide and for atomic oxygen measured by a reentry flight experiment are used to assess the modeling of this phenomenon. Flow field computations are performed using the direct simulation Monte Carlo method. Due to the relatively small number of collisions under high‐altitude, low‐density flow conditions, an overlay approach is used to simulate changes in chemical composition of trace species, including both nitric oxide and atomic oxygen. Radiative emission is calculated using a nonequilibrium radiation method. It is found that the strong degree of thermal nonequilibrium that occurs in high‐altitude, Hypersonic Flows makes the chemistry very sensitive to the vibration–dissociation coupling model. A number of such models based on continuum and particle representations of the flow are assessed. A variation in dissociation rate of up to nine orders of magnitude among these models is foun...
J. R. Torczynski - One of the best experts on this subject based on the ideXlab platform.
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DSMC Predictions of Non‐equilibrium Reaction Rates
2011Co-Authors: Ryan Bomar Bond, M. A. Gallis, J. R. TorczynskiAbstract:A set of Direct Simulation Monte Carlo (DSMC) chemical‐reaction models recently proposed by Bird and based solely on the collision energy and the vibrational energy levels of the species involved is applied to calculate non‐equilibrium chemical‐reaction rates for atmospheric reactions in Hypersonic Flows. The DSMC non‐equilibrium model predictions are in good agreement with theoretical models and experimental measurements. The observed agreement provides strong evidence that modeling chemical reactions using only the collision energy and the vibrational energy levels provides an accurate method for predicting non‐equilibrium chemical‐reaction rates.
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a kinetic theory approach for computing chemical reaction rates in upper atmosphere Hypersonic Flows
Journal of Chemical Physics, 2009Co-Authors: M. A. Gallis, Ryan Bomar Bond, J. R. TorczynskiAbstract:Recently proposed molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction-rate information) are investigated for chemical reactions occurring in upper-atmosphere Hypersonic Flows. The new models are in good agreement with the measured Arrhenius rates for near-equilibrium conditions and with both measured rates and other theoretical models for far-from-equilibrium conditions. Additionally, the new models are applied to representative combustion and ionization reactions and are in good agreement with available measurements and theoretical models. Thus, molecular-level chemistry modeling provides an accurate method for predicting equilibrium and nonequilibrium chemical-reaction rates in gases.
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Molecule-based approach for computing chemical-reaction rates in upper atmosphere Hypersonic Flows.
2009Co-Authors: M. A. Gallis, Ryan Bomar Bond, J. R. TorczynskiAbstract:This report summarizes the work completed during FY2009 for the LDRD project 09-1332 'Molecule-Based Approach for Computing Chemical-Reaction Rates in Upper-Atmosphere Hypersonic Flows'. The goal of this project was to apply a recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary nonequilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological non-equilibrium reaction-rate model, the predominant model for Hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, the difference between the two models can exceed 10 orders of magnitude. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates. Extensions of the model to reactions typically found in combustion Flows and ionizing reactions are also found to be in very good agreement with available measurements, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.
Bibin John - One of the best experts on this subject based on the ideXlab platform.
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shock wave boundary layer interactions in Hypersonic Flows
International Journal of Heat and Mass Transfer, 2014Co-Authors: Bibin John, Vinayak Kulkarni, Ganesh NatarajanAbstract:Abstract Shock-wave boundary layer interaction (SWBLI) and associated changes in wall properties for ramp induced flow breakdown have been considered in the present studies. A two dimensional finite volume based CFD solver has been developed and implemented successfully to study the SWBLI. Pressure measurements are invariantly considered in the literature for qualitative prediction of various SWBLI parameters. Hence efforts are made herewith to understand the laminar boundary layer separation in the presence of ramp induced shock wave through surface heat transfer rates, wall skin friction coefficient and wall pressure distributions. Effect of variation of freestream and wall properties along with geometric changes is considered in present studies. It has been observed from present limited investigations that ratio of wall temperature to freestream stagnation temperature is the governing parameter for SWBLI instead of the individual temperatures. Increase in Mach number is found to suppress the upstream influence which results in decrease in extent of separation. Efforts are also made to study the effect of leading edge bluntness on the SWBLI. These studies are found useful to confirm the earlier reported experimental observations regarding turbulent re-attachment.