Calculation of supersonic turbulent reacting coaxial jets
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Eklund, Dean R.↗
Engineering topics
Hassan, H. A.
Publications and source records attributed to Hassan, H. A..
Monte Carlo simulation of re-entry flows using a bimodal vibration model
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Olynick, David P.↗
Monte Carlo simulation of vibrational relaxation in nitrogen
Monte Carlo simulation of nonequilibrium vibrational relaxation of (rotationless) N2 using transition probabilities form an extended SSH theory is presented. For the range of temperatures considered, 4000-8000 K, the vibrational levels were found to be reasonably close to an equilibrium distribution at an average vibrational temperature based on the vibrational energy of the gas. As a result, they do not show any statistically significant evidence of the bottleneck observed in earlier studies of N2. Based on this finding, it appears that, for the temperature range considered, dissociation commences after all vibrational levels equilibrate at the translational temperature.
Olynick, David P.↗
An abbreviated Reynolds stress turbulence model for airfoil flows
An abbreviated Reynolds stress turbulence model is presented for solving turbulent flow over airfoils. The model consists of two partial differential equations, one for the Reynolds shear stress and the other for the turbulent kinetic energy. The normal stresses and the dissipation rate of turbulent kinetic energy are computed from algebraic relationships having the correct asymptotic near wall behavior. This allows the model to be integrated all the way to the wall without the use of wall functions. Results for a flat plate at zero angle of attack, a NACA 0012 airfoil and a RAE 2822 airfoil are presented.
Gaffney, R. L., Jr.↗
A hybrid Reynolds averaged/PDF closure model for supersonic turbulent combustion
A hybrid Reynolds averaged/assumed pdf approach has been developed and applied to the study of turbulent combustion in a supersonic mixing layer. This approach is used to address the 'laminar-like' treatment of the thermochemical terms that appear in the conservation equations. Calculations were carried out for two experiments involving H2-air supersonic turbulent mixing. Two different forms of the pdf were implemented. In general, the results show modest improvement from previous calculations. Moreover, the results appear to be somewhat independent of the form of the assumed pdf.
Frankel, Steven H.↗
Direct simulation of reentry flows with ionization
The Direct Simulation Monte Carlo (DSMC) method is applied in this paper to the study of rarefied hypersonic reentry flows. The assumptions and simplifications involved with the treatment of ionization, free electrons and the electric field are investigated. A new method is presented for the calculation of the electric field and handling of charged particles with DSMC. In addition, a two-step model for electron impact ionization is implemented. The flowfield representing a 10 km/sec shock at an altitude of 65 km is calculated. The effects of the new modeling techniques on the calculation results are presented and discussed.
Carlson, Ann B.↗
Hypersonic flow - Physical issues and computational simulation
Computational results are presented on hypersonic flows, with emphasis on thermal and chemical nonequilibrium effects and the role played by grids. The continuum equations and their boundary conditions are presented, and the direct simulation Monte Carlo method is described. The importance of using the correct computational and physical models in describing hypersonic nonequilibrium flows is demonstrated.
Hassan, H. A.↗
Numerical solutions of the complete Navier-Stokes equations
A hybrid Reynolds averaged/assumed probability density function (PDF) approach was developed and applied to the study of turbulent combustion in a supersonic mixing layer. This approach was used to address the laminar-like treatment of the thermochemical terms that appear in the conservation equations. Calculations were carried out for two experiments involving H2-air supersonic turbulent mixing. A SPARK combustion model was employed. In general, the approach shows modest improvement over previous calculations.
Hassan, H. A.↗
Grid generation and adaptation for the direct simulation Monte Carlo method
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Olynick, David P.↗
Unsteady viscous-inviscid interaction procedures for transonic airfoils using Cartesian grids
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Fenno, Charles C., Jr.↗
Study of hypersonic flow past sharp cones
Calculations using the direct simulation Monte Carlo (DSMC) method of Bird for flow past sharp cones in the near continuum to free molecule flow regime are presented and compared with experiment. It is found that results are sensitive to the grid and the interaction potential. Moreover, the time counter method was found to be as accurate as other methods when the solution is grid independent. Finally, the results show that the effects of the wake on the forebody surface properties are minimal.
Taylor, Jeff C.↗
Influence of afterbodies on AOTV flows
The role of vibration-dissociation coupling in flows representative of AOTV's with afterbodies is discussed. A physical model designed to reflect the behavior of anharmonic diatomic molecules at high temperatures was developed and incorporated into the direct simulation Monte Carlo method of Bird (1976). The model leads to reduced dissociation and increased convective heating for flows with finite catalytic surfaces.
Olynick, David P.↗
A one equation turbulence model for transonic airfoil flows
A one-equation turbulence model has been developed from available experimental observations on both attached and separated turbulence flows, and numerical results are presented for flows about NACA 0012 and RAE 2822 airfoils. The model is shown to duplicate the accurate results of the Baldwin-Lomax (1978) algebraic model for the case of attached flow. For cases of separated flow, the model is found to predict shock location and strength closer to the experimentally observed values than both the algebraic and the q-omega two-equation models.
Mitcheltree, R. A.↗
Numerical modeling of turbulent supersonic reacting coaxial jets
The paper considers the mixing and subsequent combustion within turbulent reacting shear layers. A computer program was developed to solve the axisymmetric Reynolds averaged Navier-Stokes equations. The numerical method integrates the Reynolds averaged Navier-Stokes equations using a finite volume approach while advancing the solution forward in time using a Runge-Kutta scheme. Three separate flowfields are investigated and it is found that no single turbulence model considered could accurately predict the degree of mixing for all three cases.
Eklund, Dean R.↗
Monte Carlo simulation of reentry plasmas
Attention is given to the treatment of ionization and plasma effects in the direct simulation Monte Carlo method. The requirements for accurate modeling of reentry plasmas are discussed along with the difficulties these requirements present. The current method for modeling such plasmas is reviewed and an alternative method is presented. Both methods are applied to the flow of a 10 km/s shock wave in air at 0.1 torr; a flowfield directly relevant to the projected aeroassisted orbital transfer vehicle. The results are compared and the differences between the methods are discussed.
Carlson, Ann B.↗
Direct Simulation of Reentry Flows with Ionization
The Direct Simulation Monte Carlo (DSMC) method is applied in this paper to the study of rarefied, hypersonic, reentry flows. The assumptions and simplifications involved with the treatment of ionization, free electrons and the electric field are investigated. A new method is presented for the calculation of the electric field and handling of charged particles with DSMC. In addition, a two-step model for electron impact ionization is implemented. The flow field representing a 10 km/sec shock at an altitude of 65 km is calculated. The effects of the new modeling techniques on the calculation results are presented and discussed.
Carlson, Ann B.↗
Navier-Stokes calculations using Cartesian grids. I - Laminar flows
A finite-volume formulation for the Navier-Stokes equations using Cartesian grids is used to study flows past airfoils. In addition to the solution of the complete equations, solutions for two simplified versions of the governing equations were obtained and compared with those using body-fitted grids. Results are presented for two airfoil sections, NACA 0012 and RAE 2822, for a range of Mach numbers, angles of attack, and Reynolds numbers. It is shown that the results are highly dependent on the smoothness of the surface grid. Without such smoothness, the skin friction and pressure converge to nonuniform distributions. On the other hand, when surface cells with smoothly varying areas are used, the results compared favorably with calculations employing body-fitted grids.
Frymier, Paul D., Jr.↗
Numerical solutions of the complete Navier-Stokes equations
The physical phenomena within supersonic flows that sustain chemical reactions are investigated. An earlier study to develop accurate physical models for supersonic reacting flowfields focused on 2-D laminar shear layers. The objective is to examine the mixing and subsequent combustion within turbulent reacting shear layers. To conduct this study, a computer program has been written to solve the axisymmetric Reynolds averaged Navier-Stokes equations. The numerical method uses a cell-centered finite volume approach and a Runge Kutta time stepping scheme. The Reynolds averaged equations are closed using the eddy viscosity concept. Several zero-equation models have been tested by making calculations for an H2-air nonreacting coaxial jet flow. Comparisons made with experimental data show that Cohen's eddy viscosity model provides best agreement. The finite rate chemistry model used in the study of 2-D laminar shear layers is incorporated into the computer program and data is compared from a recent experiment performed at NASA Langley.
Hassan, H. A.↗