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  • 11
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    A Fully Implicit Time Accurate Method for Hypersonic Combustion: Application to Shock-induced Combustion Instability (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A new fully implicit, time accurate algorithm suitable for chemically reacting, viscous flows in the transonic-to-hypersonic regime is described. The method is based on a class of Total Variation Diminishing (TVD) schemes and uses successive Gauss-Siedel relaxation sweeps. The inversion of large matrices is avoided by partitioning the system into reacting and nonreacting parts, but still maintaining a fully coupled interaction. As a result, the matrices that have to be inverted are of the same size as those obtained with the commonly used point implicit methods. In this paper we illustrate the applicability of the new algorithm to hypervelocity unsteady combustion applications. We present a series of numerical simulations of the periodic combustion instabilities observed in ballistic-range experiments of blunt projectiles flying at subdetonative speeds through hydrogen-air mixtures. The computed frequencies of oscillation are in excellent agreement with experimental data.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-106707 , ICOMP-94-18 , E-9069 , NAS 1.15:106707 , AIAA PAPER 94-2965 , Joint Propulsion Conference; Jun 27, 1994 - Jun 29, 1994; Indianapolis, IN; United States
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  • 12
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    Computational study of single-expansion-ramp nozzles with external burning (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A computational investigation of the effects of external burning on the performance of single expansion ramp nozzles (SERN) operating at transonic speeds is presented. The study focuses on the effects of external heat addition and introduces a simplified injection and mixing model based on a control volume analysis. This simplified model permits parametric and scaling studies that would have been impossible to conduct with a detailed CFD analysis. The CFD model is validated by comparing the computed pressure distribution and thrust forces, for several nozzle configurations, with experimental data. Specific impulse calculations are also presented which indicate that external burning performance can be superior to other methods of thrust augmentation at transonic speeds. The effects of injection fuel pressure and nozzle pressure ratio on the performance of SERN nozzles with external burning are described. The results show trends similar to those reported in the experimental study, and provide additional information that complements the experimental data, improving our understanding of external burning flowfields. A study of the effect of scale is also presented. The results indicate that combustion kinetics do not make the flowfield sensitive to scale.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-106550 , ICOMP-94-5 , E-8702 , NAS 1.15:106550 , AIAA PAPER 94-0024 , Aerospace Sciences Meeting; Jan 10, 1994 - Jan 13, 1994; Reno, NV; United States
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  • 13
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    Numerical study of shock-induced combustion in methane-air mixtures (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The shock-induced combustion of methane-air mixtures in hypersonic flows is investigated using a new reaction mechanism consisting of 19 reacting species and 52 elementary reactions. This reduced model is derived from a full kinetic mechanism via the Detailed Reduction technique. Zero-dimensional computations of several shock-tube experiments are presented first. The reaction mechanism is then combined with a fully implicit Navier-Stokes computational fluid dynamics (CFD) code to conduct numerical simulations of two-dimensional and axisymmetric shock-induced combustion experiments of stoichiometric methane-air mixtures at a Mach number of M = 6.61. Applications to the ram accelerator concept are also presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-106354 , ICOMP-93-32 , E-8138 , NAS 1.15:106354 , AIAA PAPER 93-1917 , Joint Propulsion Conference and Exhibit; Jun 28, 1993 - Jun 30, 1993; Monterey, CA; United States
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  • 14
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    Assessment of Reduced-Kinetics Mechanisms for Combustion of Jet Fuel in CFD Applications (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A computational effort was undertaken to analyze the details of fluid flow in Lean-Direct Injection (LDI) combustors for next-generation LDI design. The National Combustor Code (NCC) was used to perform reacting flow computations on single-element LDI injector configurations. The feasibility of using a reduced chemical-kinetics approach, which optimizes the reaction rates and species to model the emissions characteristics typical of lean-burning gas-turbine combustors, was assessed. The assessments were performed with Reynolds- Averaged Navier-Stokes (RANS) and Time-Filtered Navier Stokes (TFNS) time-integration, with a Lagrangian spray model with the NCC code. The NCC predictions for EINOx and combustor exit temperature were compared with experimental data for two different single-element LDI injector configurations, with 60deg and 45deg axially swept swirler vanes. The effects of turbulence-chemistry interaction on the predicted flow in a typical LDI combustor were studied with detailed comparisons of NCC TFNS with experimental data.
    Keywords: Propellants and Fuels; Fluid Mechanics and Thermodynamics
    Type: E-662714 , AIAA Propulsion and Energy 2014 Conference; Jul 28, 2014 - Jul 30, 2014; Cleveland, OH; United States
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  • 15
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    Effect of Fuel Injection and Mixing Characteristics on Pulse-Combustor Performance at High-Pressure (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Recent calculations of pulse-combustors operating at high-pressure conditions produced pressure gains significantly lower than those observed experimentally and computationally at atmospheric conditions. The factors limiting the pressure-gain at high-pressure conditions are identified, and the effects of fuel injection and air mixing characteristics on performance are investigated. New pulse-combustor configurations were developed, and the results show that by suitable changes to the combustor geometry, fuel injection scheme and valve dynamics the performance of the pulse-combustor operating at high-pressure conditions can be increased to levels comparable to those observed at atmospheric conditions. In addition, the new configurations can significantly reduce the levels of NOx emissions. One particular configuration resulted in extremely low levels of NO, producing an emission index much less than one, although at a lower pressure-gain. Calculations at representative cruise conditions demonstrated that pulse-combustors can achieve a high level of performance at such conditions.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN16221 , Joint Propulsion Conference; Jul 28, 2014 - Jul 30, 2014; Cleveland, Ohio; United States
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  • 16
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    Numerical study of shock-wave/boundary layer interactions in premixed hydrogen-air hypersonic flows (1990)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A computational study of shock wave/boundary layer interactions involving premixed combustible gases, and the resulting combustion processes is presented. The analysis is carried out using a new fully implicit, total variation diminishing (TVD) code developed for solving the fully coupled Reynolds-averaged Navier-Stokes equations and species continuity equations in an efficient manner. To accelerate the convergence of the basic iterative procedure, this code is combined with vector extrapolation methods. The chemical nonequilibrium processes are simulated by means of a finite-rate chemistry model for hydrogen-air combustion. Several validation test cases are presented and the results compared with experimental data or with other computational results. The code is then applied to study shock wave/boundary layer interactions in a ram accelerator configuration. Results indicate a new combustion mechanism in which a shock wave induces combustion in the boundary layer, which then propagates outwards and downstream. At higher Mach numbers, spontaneous ignition in part of the boundary layer is observed, which eventually extends along the entire boundary layer at still higher values of the Mach number.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-103273 , E-5715 , ICOMP-90-22 , NAS 1.15:103273 , AIAA PAPER 91-0413 , Aerospace Sciences Meeting; Jan 07, 1991 - Jan 10, 1991; Reno, NV; United States
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  • 17
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    Dual-Mode Free-Jet Combustor (2017)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The dual-mode free-jet combustor concept, pictured in figure 1, is described. It was introduced in 2010 as a wide- operating-range propulsion device using a novel supersonic free-jet combustion process. The unique feature of the free-jet combustor pictured in figure 1a, is supersonic combustion in an unconfined free-jet that traverses a larger subsonic combustion chamber to a variable nozzle. During this mode of operation, the propulsive stream is not in contact with the combustor walls, and equilibrates to the combustion chamber pressure. To a first order, thermodynamic efficiency is similar to that of a traditional scramjet under the assumption of constant-pressure combustion. Qualitatively, a number of possible benefits to this approach are obvious.
    Keywords: Aircraft Propulsion and Power
    Type: Paper No. 22537 , GRC-E-DAA-TN45949 , International Society of Air Breathing Engines (ISABE 2017); Sep 03, 2017 - Sep 08, 2017; Manchester, England; United Kingdom
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  • 18
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    Dual-Mode Free-Jet Combustor (2017)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The dual-mode free-jet combustor concept, pictured in figure 1, is described. It was introduced in 2010 as a wide- operating-range propulsion device using a novel supersonic free-jet combustion process. The unique feature of the free-jet combustor pictured in figure 1a, is supersonic combustion in an unconfined free-jet that traverses a larger subsonic combustion chamber to a variable nozzle. During this mode of operation, the propulsive stream is not in contact with the combustor walls, and equilibrates to the combustion chamber pressure. To a first order, thermodynamic efficiency is similar to that of a traditional scramjet under the assumption of constant-pressure combustion. Qualitatively, a number of possible benefits to this approach are obvious.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN44286 , International Symposium on Air Breathing Engines (ISABE); Sep 03, 2017 - Sep 08, 2017; Manchester; United Kingdom
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  • 19
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    Airbreathing Pulse Detonation Engine Performance (2002)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: This paper presents performance results for pulse detonation engines (PDE) taking into account the effects of dissociation and recombination. The amount of sensible heat recovered through recombination in the PDE chamber and exhaust process was found to be significant. These results have an impact on the specific thrust, impulse and fuel consumption of the PDE.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2002-211575 , NAS 1.15:211575 , E-13359 , ICOMP-2002-02 , Combustion, Airbreathing Propulsion, Propulsion Systems Hazards, and Modelling and Simulation Subcommittees Joint Meeting; 8-12 Apr. 202; Destin, FL; United States
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  • 20
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    Real Gas Effects on the Performance of Hydrocarbon-fueled Pulse Detonation Engines (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper presents results for a single-pulse detonation tube wherein the effects of high temperature dissociation and the subsequent recombination influence the sensible heat release available for providing propulsive thrust. The study involved the use of ethylene and air at equivalence ratios of 0.7 and 1.0. The real gas effects on the sensible heat release were found to be significantly large so as to have an impact on the thrust, impulse and fuel consumption of a PDE.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2003-212211 , E-13819 , NAS 1.15:212211 , AIAA Paper 2003-0712 , ICOMP-2003-02 , 41st Aerospace Sciences Meeting; Jan 06, 2003 - Jan 09, 2003; Reno, NV; United States
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