Showing papers on "Scramjet published in 1991"

Dynamics and control of hypersonic vehicles - The integration challenge for the 1990's

Abstract: The dynamic characteristics of hypersonic vehicles are reviewed, with special attention to the interactions between the airframe, engine, and structural dynamics. Based on a preliminary investigation of the dynamics of a generic vehicle configuration similar to the X-30 with Scramjet propulsion, an assessment of these interactions is presented. The control effectors include aerodynamic pitch-control surfaces, as well as engine fuel flow and diffuser area ratio. The study configuration is statically instable in pitch, and exhibits strong airframe/engine/elastic coupling in the attitude dynamics and engine responses. This strong coupling will require a highly integrated airframe-engine control system, and the performance of the attitude control system will be contingent upon the ability to adequately deal with the structural aeroelastic response and engine dynamics.

Parametric study of airframe-integrated scramjet cooling requirement

Abstract: In a previous report, scramjet engine characteristics of different propellant-fed cycles were compared and engine performances were discussed. In this study, the cooling requirement of a hydrogen-fueled airframe-integrated scramjet engine as well as an airframe was examined, and effects of various parameters including flight Mach number, flight dynamic pressure, engine wall temperature, and engine scale, on the engine characteristics were analyzed. The coolant required for the airframe was about 20% of the total coolant. Simple equations that correlate coolant flow rate with those parameters were derived. A B b CD Cp 7sp t M m P Q q

Rapid methodology for design and performance prediction of integrated supersonic combustion ramjet engine

Abstract: The design integration of a supersonic combustion ramjet engine (SCRAMJET) with an airframe dictates the mission success of transatmospheric or hypersonic cruise vehicles. Special interest must be given for the hypersonic atmospheric boost phase of the mission where most of the propulsive energy is expended. For this purpose, the operational efficiency is established by the effective specific impulse and the thrust to weight ratio of the accelerating vehicle. In order to analyze the foregoing problems, a methodology is developed, which permits a quick performance evaluation of an idealized, integrated SCRAMJET vehicle for preliminary design analysis. The capabilities of methodology are 1) designing an integrated vehicle consisting of the forebody inlet, supersonic flow combustor and afterbody expansion nozzle; 2) generating the design and off-design performance data; and 3) performing many design iterations for tradeoff studies. Samples of the design and off-design performance analysis of generic hypersonic vehicles are presented. The methodology is suitable to be programmed and executed on a personal computer.

An Investigation into the Performance Characteristics of a Solid Fuel SCRAMJET Propulsion Device

Abstract: : An investigation was conducted to evaluate the performance qualities of a supersonic ramjet propulsion device (SCRAMJET) using a solid fuel The fuel grains were fabricated from Plexiglas and were cylindrical, with an axisymmetric, circular perforation that diverged in the downstream direction A small amount of hydrogen gas was required in an initial recirculation zone in order to sustain combustion With Combustor inlet conditions of 150 psia, 1000 R, and a Mach number of 15, a combustor exit Mach number of approximately 14 was maintained Due to poor mixing conditions, the combustion efficiency of the solid fuel only 57%

Mixing and mixing enhancement in supersonic reacting flowfields

Abstract: Propulsion systems planned for use late in this century and beyond will require appropriate physical models for describing supersonic combustion and numerical techniques for solving the model governing equations. A computer program to study these flows is reported which considers the multicomponent diffusion and convection of important chemical species, the finite-rate reaction of these species, and the resulting interaction of the field mechanics and the chemistry. The application of the program to a spatially developing and reacting mixing layer, which serves an an excellent physical model for the mixing and reaction processes that take place in a scramjet combustor, is reported. Several techniques to enhance the fuel-air mixing and growth of that layer and improve its overall combustion efficiency are considered.

Mach 2 and Mach 3 mixing and combustion in scramjets

Abstract: Experimental and theoretical studies are being conducted to explore techniques to enhance mixing in scramjet combustors using parallel fuel injection from the base of swept and unswept wall-mounted ramps. Parallel injection may be useful in high speed scramjets due to the thrust contributed by the momentum of expanding fuel that has been heated in the vehicle cooling cycle. The experiments reported herein were conducted using Mach 2 and 3 combustor inlet conditions. Supporting computational and cold flow studies indicated that the observed enhanced mixing for the swept ramp configuration is primarily due to the substantially higher degree of vorticity and entrainment generated by the swept trailing edges.

Analytical and experimental investigations of the oblique detonation wave engine concept

Abstract: Wave combustors, which include the Oblique Detonation Wave Engine (ODWE), are attractive propulsion concepts for hypersonic flight. These engines utilize oblique shock or detonation waves to rapidly mix, ignite, and combust the air-fuel mixture in thin zones in the combustion chamber. Benefits of these combustion systems include shorter and lighter engines which will require less cooling and can provide thrust at higher Mach numbers than conventional scramjets. The wave combustor's ability to operate at lower combustor inlet pressures may allow the vehicle to operate at lower dynamic pressures which could lessen the heating loads on the airframe. The research program at NASA-Ames includes analytical studies of the ODWE combustor using CFD codes which fully couple finite rate chemistry with fluid dynamics. In addition, experimental proof-of-concept studies are being carried out in an arc heated hypersonic wind tunnel. Several fuel injection designs were studied analytically and experimentally. In-stream strut fuel injectors were chosen to provide good mixing with minimal stagnation pressure losses. Measurements of flow field properties behind the oblique wave are compared to analytical predictions.

Propellant feed system of a regeneratively cooled scramjet

Abstract: An expander cycle for an airframe-integrated hydrogen-fueled scramjet is analyzed to study regenerative cooling characteristics and overall specific impulse. Below Mach 10, the specific impulse and thrust coincide with the reference values. At Mach numbers above 10, a reduction of the specific impulse occurs due to the coolant flow rate requirement, which is accompanied by an increase of thrust. It is shown that the thrust may be increased by injecting excess fuel into the combustor to compensate for the decrease of the specific impulse. 9 refs.

Mixing enhancement of reacting parallel fuel jets in a supersonic combustor

Abstract: Pursuant to a NASA-Langley development program for a scramjet HST propulsion system entailing the optimization of the scramjet combustor's fuel-air mixing and reaction characteristics, a numerical study has been conducted of the candidate parallel fuel injectors. Attention is given to a method for flow mixing-process and combustion-efficiency enhancement in which a supersonic circular hydrogen jet coflows with a supersonic air stream. When enhanced by a planar oblique shock, the injector configuration exhibited a substantial degree of induced vorticity in the fuel stream which increased mixing and chemical reaction rates, relative to the unshocked configuration. The resulting heat release was effective in breaking down the stable hydrogen vortex pair that had inhibited more extensive fuel-air mixing.

Computational and experimental aftbody flow fields for hypersonic, airbreathing configurations with scramjet exhaust flow simulation

Abstract: Computational results are presented for three issues pertinent to hypersonic, airbreathing vehicles employing scramjet exhaust flow simulation. The first issue consists of a comparison of schlieren photographs obtained on the aftbody of a cruise missile configuration under powered conditions with two-dimensional computational solutions. The second issue presents the powered aftbody effects of modeling the inlet with a fairing to divert the external flow as compared to an operating flow-through inlet on a generic hypersonic vehicle. Finally, a comparison of solutions examining the potential of testing powered configurations in a wind-off, instead of a wind-on, environment, indicate that, depending on the extent of the three-dimensional plume, it may be possible to test aftbody powered hypersonic, airbreathing configurations in a wind-off environment.

Experimental study on autoignition in a scramjet combustor

Abstract: A UTOIGNITION characteristics of hydrogen fuel in a scramjet combustor were examined using a direct-connect test apparatus with particular reference to the effect of fuel injection patterns. Autoignition behavior fell into four distinct categories, separated by the three bounding curves. One of the boundaries was independent of fuel injection patterns, while the others significantly depended on them. In the case of fuel injection from a single wall or from a single orifice, local flame quenching caused by expansion wave emanating from the step on the opposite wall was observed. Compared with injection from a single orifice, injection from multiple orifices appreciably enhanced autoignition. The reason for this is that fuel jets from adjacent orifices and from the opposite wall tended to attenuate the local flame quenching caused by the expansion waves from the opposite wall. Ignition limit curves derived from the present experiment were compared with an autoignition criteria proposed by Huber et al. They agree well in the case of fuel injection from a single orifice. For the case of injection from multiple orifices, however, the agreement is poor.

A Computational and Experimental Investigation of a Three-Dimensional Hypersonic Scramjet Inlet Flow Field

Abstract: A combined computational and experimental parametric study of the internal aerodynamics of a generic three dimensional sidewall compression scramjet inlet configuration was performed. The study was designed to demonstrate the utility of computational fluid dynamics as a design tool in hypersonic inlet flow fields, to provide a detailed account of the nature and structure of the internal flow interactions, and to provide a comprehensive surface property and flow field database to determine the effects of contraction ratio, cowl position, and Reynolds number on the performance of a hypersonic scramjet inlet configuration.

Hypersonic Turbomachinery- Based Air-Breathing Engines for the Earth-to-Orbit Vehicle

Abstract: Hypersonic air-breathing engines will make the Earth-to-orbit vehicle completely different from the present one powered by rocket engines. The space plane propelled by a certain hypersonic air-breathing propulsion system is expected to appear in the next century. The turbomachinery-based engine (turboengine) is a candidate for the space plane propulsion system and will be combined with scramjet and rocket engines. Turboengines, including turboramjet, air-turboramjet, and their modifications, may be applied as the accelerators to the space plane having a high specific impulse at a rather low supersonic Mach number. Here, a conceptual study of these turboengines with preliminary system design, performance calculations, and consideration of relative merits of the engine concepts is performed for the configuration, performance, weight, and size. An engine evaluation with mission capability of the space plane for assumed requirements is made. As a result, engine performance depends on the liquid oxygen utilization, and weight and size of the engine are important factors for application to the space plane. Thus a certain optimization of the engine system itself and of a combination of the engines would be necessary.

Contraction ratio effects in a generic sidewall compression scramjet inlet - A computational and experimental investigation

Abstract: Computed and experimental data on a generic three-dimensional sidewall compression scramjet inlet with a leading edge sweep of 45 degrees at Mach 20 are presented. A three-dimensional Navier-Stokes code was adapted to perform preliminary parametric studies leading to the present configuration. Following the design phase, the code was then employed as an analysis tool to provide a better understanding of the flow field and the experimental static and pitot pressure data. The model possessed 240 static pressure orifices distributed on the forebody plane, sidewalls, and cowl and was tested in the 31 Inch Mach 10 facility at the NASA Langley Research Center. Pitot rakes were employed to map the entrance and exit planes. The contraction ratio was observed to have a dominant effect on the inlet shock structure and performance; these effects are the emphasis of the present report. In addition to pressure measurements, oil flows were used for further visualization and comparison with computation.

Inviscid analysis of a dual mode scramjet inlet

Abstract: A three-dimensional inviscid flow computation was made on a dual mode scramjet inlet model that had been tested in the wind tunnels. An Euler solver based on a high accuracy total variation diminishing scheme was used to carry out the analysis. The objective was to establish three-dimensional scramjet inlet computational fluid dynamics capability and to evaluate the applicability of Euler solutions for inlet performance calculation. The computations were made for freestream Mach numbers 2 and 5. A postprocessor was developed to calculate the inlet performance. Comparison between computed and available test data showed the Euler analysis was able to predict the trend of the inlet performance and provide insight of the flowfield.

Method of operating a scramjet including integrated inlet and combustor

Abstract: A scramjet engine is disclosed which is effective for use in a hypersonic aircraft as an aircraft-integrated scramjet engine. The engine includes a first surface having an aft facing step, and a cowl upper surface spaced from the first surface to define an integrated inlet-combustor therebetween. A method of operating the engine includes injecting fuel into the inlet-combustor at the step for mixing fuel with supersonic airflow for generating supersonic combustion gases in the inlet-combustor. In the preferred embodiment of the invention, the fuel is injected to create a fluid boundary defining a subsonic fuel zone and a supersonic fluid zone. The fluid boundary is variable and eliminates start and unstart problems requiring variable inlet geometry in a conventional scramjet engine.

Engineering model for analysis of scramjet combustor performance with finite-rate chemistry

Abstract: An engineering model of diffusion and reaction-limited supersonic combustion is described. The key feature of this model is that it divides the flowfield into three parallel, one-dimensional streams: 1) the fuel stream, 2) the oxidizer stream, and 3) the product stream. Fuel and oxidizer are continuously fed into the product stream in accordance with an empirical mixing model and allowed to react at a finite rate. Comparisons with experimental data for hydrogen-air combustion are presented. The model is clearly oversimplified compared to the complex two- and three-dimensional turbulent mixing and induced shock train processes known to exist in supersonic combustors. Nevertheless, it includes sufficient physics to provide reasonably good agreement with the data and enables rapid interpretation of the global features of the experiments. Accordingly, it may be useful in conceptual design studies.

CFD Evaluation of Mach 17 HYPULSE Scramjet Combustor Data

Abstract: Three-dimensional finite rate chemistry solutions are performed on a single fuel injector configuration. The results are compared with limited experimental data obtained from the HYPULSE expansion tube facility at simulated flight Mach 17 flow conditions. All comparisons, except for wall heat flux, were in excellent agreement. Key findings from this study are useful in interpretation of the experimental measurements.

Flow analysis and design optimization methods for nozzle afterbody of a hypersonic vehicle

Abstract: This report summarizes the methods developed for the aerodynamic analysis and the shape optimization of the nozzle-afterbody section of a hypersonic vehicle. Initially, exhaust gases were assumed to be air. Internal-external flows around a single scramjet module were analyzed by solving the three dimensional Navier-Stokes equations. Then, exhaust gases were simulated by a cold mixture of Freon and Argon. Two different models were used to compute these multispecies flows as they mixed with the hypersonic airflow. Surface and off-surface properties were successfully compared with the experimental data. In the second phase of this project, the Aerodynamic Design Optimization with Sensitivity analysis (ADOS) was developed. Pre and post optimization sensitivity coefficients were derived and used in this quasi-analytical method. These coefficients were also used to predict inexpensively the flow field around a changed shape when the flow field of an unchanged shape was given. Starting with totally arbitrary initial afterbody shapes, independent computations were converged to the same optimum shape, which rendered the maximum axial thrust.

An experimental investigation of a supersonic vortical flow

Abstract: Although much research has been done on subsonic vortical flow, the current understanding of these flows remains limited. The effect is characterized of adding swirl to a supersonic jet. The motive is to study the enhancement of supersonic mixing in order to provide more efficient fuel injectors for supersonic combustion (scramjet) engines. The vortical flow was created by tangential injection into a swirl chamber ahead of a converging and/or diverging nozzle. The amount of swirl was varied by changing the number of tangential injection holes and with the removal of the end piece, the jet could be run without swirl. Shadowgraphy, conventional schlieren, and focusing schlieren were used to obtain a qualitative understanding of the jet flow structure. It was determined that an increase in swirl produced an increase in the shear layer growth. Pressure and temperature probes were used to obtain more flow data. The probe data compared favorably with the theoretical calculations, except in the viscous core where viscous effects were not considered negligible. These results verified that a supersonic vortical flow was being created with a maximum helix angle of 33 degs.

Instantaneous planar visualization of reacting supersonic flows using silane seeding

Abstract: A new visualization technique for reacting flows has been developed. This technique, which is suitable for supersonic combustion flows, has been demonstrated on a scramjet combustor model. In this application, gaseous silane (SiH4) was added to the primary hydrogen fuel. When the fuel reacted, so did the (SiH4), producing silica (SiO2) particles in situ. The particles were illuminated with a laser sheet formed from a frequency-doubled Nd:YAG laser (532 nm) beam and the Mie scattering signal was imaged. These planar images of the silica Mie scattering provided instantaneous 'maps' of combustion progress within the turbulent reacting flowfield.

Wind tunnel blockage study of a generic three-dimensional sidewall compression scramjet inlet at Mach 10

Abstract: A large scale model of a generic three-dimensional sidewall compression scramjet inlet has been designed based on the results of a computational parametric study for testing in the 31-inch Mach 10 Hypersonic Wind Tunnel at the NASA Langley Research Center. In order to increase the instrumentation density in interaction regions for a highly instrumented model, it is desirable to make the model as large as possible. When the cross-sectional area of a model becomes large relative to the inviscid core size of the tunnel, the effects of blockage must be considered. In order to assess these effects, a blockage model (an inexpensive, much less densely instrumented version of the configuration) was fabricated for preliminary testing. Since it was desired to determine both the effect of the model on the performance of the wind tunnel and also to determine if the inlet would start, the model possessed a total of 32 static pressure orifices distributed on the forebody plane and sidewalls; seventeen static pressure orifices on the tunnel wall and 3 pitot probes on the model monitored the tunnel performance. This paper presents the design considerations in the development of the wind tunnel model and the blockage aspects of the effects of contraction ratio, cowl location, Reynolds number, and angle of attack.

Determination of Cycle Configuration of Gas Turbines and Aircraft Engines by an Optimization Procedure

Abstract: This paper is devoted to the analyses and optimization of simple and sophisticated cycles, particularly for various gas turbine engines and aero-engines (including the scramjet engine) to achieve maximum performance. The optimization of such criteria as thermal efficiency, specific output, and total performance for gas turbine engines, and overall efficiency, nondimensional thrust, and specific impulse for aero-engines has been performed by the optimization procedure with the multiplier method. Comparison of results with analytical solutions establishes the validity of the optimization procedure.

Waves and thermodynamics in high Mach number propulsive ducts

Abstract: The propulsive effects of waves in ducts, especially at high Mach numbers, are investigated, focusing on drag and thrust and on the conversion of heat into waves which produce thrust. It is shown that essentially all of the work done by an expanding fluid passing through a duct at high Mach number is delivered in the form of waves, and that duct surface angles exist that are optimum for the production of thrust from a wave. The effects of wave phenomena on drag and thrust are considered by extending the concept of a Busemann biplane into that of a 'Busemann scramjet, taking 'off-design' performance into account. An idealized model of a streamtube with heat addition is developed, and flow mechanisms involved in generating thrust by the expansion of this streamtube in an exhaust nozzle are examined.

Tangential Mass Addition for Shock/Boundary-Layer Interaction Control in Scramjet Inlets

Abstract: A series of tests are being performed to investigate and characterize shock-wave/boundary-layer interactions typical of hypersonic inlets and to develop methods of controlling, through the use of tangential mass addition, regions of shock-induced separation. The major objectives are being accomplished in a multiphase experimental test program with complementary application of computational techniques. Presented herein are results from the proof-of-concept phase of testing. The feasibility of using Mach 3 tangential air injection to eliminate separation associated with the cowl-shock/innerbody boundary-layer interaction in a scramjet inlet model has been demonstrated. The experimental test program was complemented by a computational investigation that demonstrated the importance of mass addition injector location relative to the shock/boundary-layer interaction region.

A parametric experimental investigation of a scramjet nozzle at Mach 6 with Freon and argon or air used for exhaust simulation

Abstract: A parametric experimental investigation of a scramjet nozzle was conducted with a gas mixture used to simulate the scramjet engine exhaust flow at a free-stream Reynolds number of approximately 6.5 x 10(exp 6) per foot. External nozzle surface angles of 16, 20, and 24 deg were tested with a fixed-length ramp and for cowl internal surface angles of 6 and 12 deg. Pressure data on the external nozzle surface were obtained for mixtures of Freon and argon gases with a ratio of specific heats of about 1.23, which matches that of a scramjet exhaust. Forces and moments were determined by integration of the pressure data. Two nozzle configurations were also tested with air used to simulate the exhaust flow. On the external nozzle surface, lift and thrust forces for air exhaust simulation were approximately half of those for Freon-argon exhaust simulation and the pitching moment was approximately a third. These differences were primarily due to the difference in the ratios of specific heats between the two exhaust simulation gases. A 20 deg external surface angle produced the greatest thrust for a 6 deg cowl internal surface angle. A flow fence significantly increased lift and thrust forces over those for the nozzle without a flow fence.