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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Conical detonation waves - A comparison of theoretical and numerical results

A predictive capability for conical oblique detonation waves (ODWs) is discussed with particular attention given to the special case of an axisymmetric conical projectile, which yields necessary conditions for attached waves. A multidimensional numerical model was used to study the influence of a finite Damkoehler number (Da) and viscosity on the formation of a conical ODW. The ODW is predicted for Da on the order of 10, and is found to be important in the ODW formation. For a Da of 1, shock induced combustion is predicted. Simulations of the experimental geometry showed general agreement with experimental flow features, but underpredicted the shock angle. It is suggested that this difference may be caused by inadequate boundary layer resolution, lack of grid orthogonality at the cone surface, and an inappropriate chemical mechanism.

Fort, James A.↗
NASA NTRS1993

Portable fiber optic coupled Doppler interferometer system for detonation and shock wave diagnostics

Testing and analysis of shock wave characteristics such as detonators and ground shock propagation frequently require a method of measuring velocity and displacement of the surface of interest. One method of measurement is Doppler interferometry. The VISAR (Velocity Interferometer System for Any Reflector) uses Doppler interferometry and has gained wide acceptance as the preferred tool for shock measurement. An important asset of VISAR is that it measures velocity and displacement nonintrusively.

Fleming, Kevin J.↗
NASA NTRS1992

Comparison of numerical oblique detonation solutions with an asymptotic benchmark

In order to have confidence in a numerical method, the verification of its reproduction of known benchmark analytic solutions for simple model problems is of great importance. Attention is presently given to a novel benchmarking procedure for numerical models of high speed, reactive 2D flows. The procedure is illustrated by comparing asymptotic and numerical solutions for oblique detonations in which an attached oblique shock is followed by an exothermic reaction with a thick reaction zone.

Grismer, Matthew J.↗
NASA NTRS1940

Effect of Fuel-Air Ratio, Inlet Temperature, and Exhaust Pressure on Detonation

An accurate determination of the end-gas condition was attempted by applying a refined method of analysis to experimental results. The results are compared with those obtained in Technical Report no. 655. The experimental technique employed afforded excellent control over the engine variables and unusual cyclic reproducibility. This, in conjunction with the new analysis, made possible the determination of the state of the end-gas at any instant to a fair degree of precision. Results showed that for any given maximum pressure the maximum permissible end-gas temperature increased as the fuel-air ratio was increased. The tendency to detonate was slightly reduced by an increase in residual gas content resulting from an increase in exhaust backpressure with inlet pressure constant.

Taylor, E S↗
NASA NTRS1994

The delayed-detonation model of a type Ia supernovae. 1: The deflagration phase

The nature of the 'delayed detonation' mechanism of Khokhlov for the explosion of Type Ia supernovae is investigated by using two-dimensional numerical hydrodynamics simulations. A new algorithm is used to treat the deflagration front. Assuming that it propagates locally at the laminar flame speed, the deflagration is insufficient to unbind the star. Expansion shuts of the flame; much of this small production of iron group nuclei occurs at lower densities, which reduces the electron-capture problem. The burning front does become wrinkled, but the wavelength of the instability is much larger than the computational grid size and is resolved; this is consistent with previous analysis. Because the degenerate star has an adiabatic exponent only slightly above 4/3, the energy released by deflagration drives a pulsation of large amplitude. During the first expansion phase, adiabatic cooling shuts off the burning, and a Rayleigh-Taylor instability then gives mixing of high-entropy ashes with low-entropy fuel. During the first contraction phase, compressional heating reignites the material. This paper deals with the deflagration phase, from the onset of burning, through expansion and quenching of the flame, to the first contraction.

Arnett, David↗
NASA NTRS1994

EBW's and EFI's: The other electric detonators

Exploding Bridgewire Detonators (EBW) and Exploding Foil Initiators (EFI) which were originally developed for military applications, have found numerous uses in the non-military commercial market while still retaining their military uses. While not as common as the more familiar hot wire initiators, EBW's and EFI's have definite advantages in certain applications. These advantages, and disadvantages, are discussed for typical designs.

Ron Varosh↗
NASA NTRS1994

Portable, solid state, fiber optic coupled Doppler interferometer system for detonation and shock diagnostics

VISAR (Velocity Interferometer System for Any Reflector) is a specialized Doppler interferometer system that is gaining world-wide acceptance as the standard for shock phenomena analysis. The VISAR's large power and cooling requirements, and the sensitive and complex nature of the interferometer cavity have restricted the traditional system to the laboratory. This paper describes the new portable VISAR, its peripheral sensors, and the role it played in optically measuring ground shock of and underground nuclear detonation. The Solid State VISAR uses a prototype diode pumped Nd:YAG laser and solid state detectors that provide a suitcase-size system with low power requirements. A special window and sensors were developed for fiber optic coupling (1 kilometer long) to the VISAR. The system has proven itself as a reliable, easy to use instrument that is capable of field test use and rapid data reduction using only a notebook personal computer (PC).

Fleming, K. J.↗
NASA NTRS1996

Pulse Detonation Engine Air Induction System Analysis

A preliminary mixed-compression inlet design concept for potential pulse-detonation engine (PDE) powered supersonic aircraft was defined and analyzed. The objectives of this research were to conceptually design and integrate an inlet/PDE propulsion system into a supersonic aircraft, perform time-dependent CFD analysis of the inlet flowfield, and to estimate the installed PDE cycle performance. The study was baselined to a NASA Mach 5 Waverider study vehicle in which the baseline over/under turboramjet engines were replaced with a single flowpath PDE propulsion system. As much commonality as possible was maintained with the baseline configuration, including the engine location and forebody lines. Modifications were made to the inlet system's external ramp angles and a rotating cowl lip was incorporated to improve off-design inlet operability and performance. Engines were sized to match the baseline vehicle study's ascent trajectory thrust requirement at Mach 1.2. The majority of this study was focused on a flight Mach number of 3.0. The time-dependent Navier Stokes CFD analyses of a two-dimensional approximation of the inlet was conducted for the Mach 3.0 condition. The Lockheed Martin Tactical Aircraft Systems-developed FALCON CFD code with a two equation 'k-1' turbulence model was used. The downstream PDE was simulated by an array of four sonic nozzles in which the flow areas were rapidly varied in various opening/closing combinations. Results of the CFD study indicated that the inlet design concept operated successfully at the Mach 3.0 condition, satisfying mass capture, total pressure recovery, and operability requirements. Time-dependent analysis indicated that pressure and expansion waves from the simulated valve perturbations did not effect the inlet's operability or performance.

Pegg, R. J.↗
NASA NTRS2001

Role of Air-Breathing Pulse Detonation Engines in High Speed Propulsion

In this paper, the effect of flight Mach number on the relative performance of pulse detonation engines and gas turbine engines is investigated. The effect of ram and mechanical compression on combustion inlet temperature and the subsequent sensible heat release is determined. Comparison of specific thrust, fuel consumption and impulse for the two engines show the relative benefits over the Mach number range.

Povinelli, Louis A.↗
NASA NTRS2002

Airbreathing Pulse Detonation Engine Performance

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.

Povinelli, Louis A.↗
NASA NTRS2002

Airbreathing Pulse Detonation Engine Performance

This paper presents performance results for pulse detonation engines 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.

Povinelli, Louis A.↗
NASA NTRS2002

Progress in the Development of a Nozzle Design Methodology for Pulsed Detonation Engines

The Johns Hopkins University Applied Physics Laboratory (JHU/APL), in support of the NASA Glenn Research Center (NASA GRC), is investigating performance methodologies and system integration issues related to Pulsed Detonation Engine (PDE) nozzles. The primary goal of this ongoing effort is to develop design and performance assessment methodologies applicable to PDE exit nozzle(s). APL is currently focusing its efforts on a common plenum chamber design that collects the exhaust products from multiple PDE tubes prior to expansion in a single converging-diverging exit nozzle. To accomplish this goal, a time-dependent, quasi-one-dimensional analysis for determining the flow properties in and through a single plenum and exhaust nozzle is underway. In support of these design activities, parallel modeling efforts using commercial Computational Fluid Dynamics (CFD) software are on-going. These efforts include both two and three-dimensional as well as steady and time-dependent computations to assess the flow in and through these devices. This paper discusses the progress in developing this nozzle design methodology.

Leary, B. A.↗
NASA NTRS2002

Simplified Analysis of Pulse Detonation Rocket Engine Blowdown Gasdynamics and Performance

Pulse detonation rocket engines (PDREs) offer potential performance improvements over conventional designs, but represent a challenging modellng task. A simplified model for an idealized, straight-tube, single-shot PDRE blowdown process and thrust determination is described and implemented. In order to form an assessment of the accuracy of the model, the flowfield time history is compared to experimental data from Stanford University. Parametric Studies of the effect of mixture stoichiometry, initial fill temperature, and blowdown pressure ratio on the performance of a PDRE are performed using the model. PDRE performance is also compared with a conventional steady-state rocket engine over a range of pressure ratios using similar gasdynamic assumptions.

Morris, C. I.↗
NASA NTRS2003

Real Gas Effects on the Performance of Hydrocarbon-fueled Pulse Detonation Engines

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.

Povinelli, Louis A.↗
NASA NTRS2002

Quasi 1-D Study of Pulse Detonation Rocket Engine Blowdown Gasdynamics and Performance

Pulse detonation rocket engines (PDREs) offer potential performance improvements over conventional designs, but represent a challenging modeling task. A quasi 1-D, finite-rate chemistry CFD model for a PDRE is described and implemented. A parametric study of the effect of blowdown pressure ratio on the performance of several different PDRE nozzle configurations is reported.

Morris, Christopher I.↗
NASA NTRS2003

Pulse Detonation Rocket Engine Research at NASA Marshall

This viewgraph representation provides an overview of research being conducted on Pulse Detonation Rocket Engines (PDRE) by the Propulsion Research Center (PRC) at the Marshall Space Flight Center. PDREs have a theoretical thermodynamic advantage over Steady-State Rocket Engines (SSREs) although unsteady blowdown processes complicate effective use of this advantage in practice; PRE is engaged in a fundamental study of PDRE gas dynamics to improve understanding of performance issues. Topics covered include: simplified PDRE cycle, comparison of PDRE and SSRE performance, numerical modeling of quasi 1-D rocket flows, time-accurate thrust calculations, finite-rate chemistry effects in nozzles, effect of F-R chemistry on specific impulse, effect of F-R chemistry on exit species mole fractions and PDRE performance optimization studies.

Morris, Christopher I.↗