Matthew L. Fotia

Ram-Scram Transition and Flame/Shock-Train Interactions in a Model Scramjet Experiment

The behavior of a ram-scram transition was examined using a direct-connect model scramjet experiment along with pressure measurements and high-speed laser interferometry. The work quantifies the sudden change in the wall static pressure profile and flame position that occurs as the downstream boundary condition abruptly changes when the flow becomes unchoked. Transition was studied in three ways; as a quasi-steady phenomenon due to slow decreases in fuel flow rate, or as caused by rapid variations in either fuel flow rate or test-section wall temperature. A regime diagram was constructed that plots the measured ram-scram transition boundary. Under certain conditions some periodic low-frequency oscillations of the flame position occur and they are shown to be correlated with oscillations of the upstream precombustion pseudoshock. A self-sustaining shear-layer instability, associated with the flameholding cavity, is believed to be the mechanism causing this behavior. The relevant time scales associated with...

Isolator-Combustor Interactions in a Direct-Connect Ramjet-Scramjet Experiment

Isolator–combustor interactions are measured in a direct-connect dual-mode ramjet-scramjet experiment. An operating point approach is used to create amapping of the coupling effects between the isolator geometry, inlet flow conditions, and fuel injector behavior. The resulting isolator/injector coupling map provides a description of the response of the isolator to particular injector performance and the effective blockage it induces on the isolator flow. Existing models and correlations predicting the pressure rise across a pseudoshock and its resultant length were evaluated through comparisonwithmeasurementsmade in a heated-flow isolator duct that is coupled to a hydrogenair combustor. The observation of a normal-to-oblique shock-train transitionmechanism has led to the development of a revised shock-train operating regime description that takes into account the impact of Mach number and maximum pressure recovery on the shock configurations present in the isolator.

Experimental Study of the Performance of a Rotating Detonation Engine with Nozzle

A rotating detonation engine is experimentally tested with various nozzle configurations for the purpose of measuring the propulsive performance of these devices in terms of thrust and specific impulse. Particular attention is given to comparing different internal nozzle configurations, which include bluff body, aerospike, and choked aerospike arrangements. The nozzle throat exit choke present in the rotating detonation engine exhaust is analyzed to provide insight into the stagnation pressure gain nature of the device.

Reduced-Order Modeling of Turbulent Reacting Flows with Application to Ramjets and Scramjets

DOI: 10.2514/1.50272 A new engine model has been developed for applications requiring run times shorter than a few seconds, such as design optimization or control evaluation. A reduced-order model for mixing and combustion has been developed that is based on nondimensional scaling of turbulent jets in crossflow and tabulated presumed probability distribution function flamelet chemistry. The three-dimensional information from these models is then integrated across cross-sectional planes so that a one-dimensional profile of the reaction rate of each species can be established. Finally, the one-dimensional conservation equations are integrated along the downstream axial direction and the longitudinal evolution of the flow can be computed. The reduced-order model accurately simulates real-gas effects such as dissociation, recombination, and finite rate chemistry for geometries for which the main flow is nearly onedimensional. Thus, this approach may be applied to any flowpath in which this is the case; ramjets, scramjets, and rockets are good candidates. Comparisons to computational fluid dynamics solutions and experimental data were conducted to determine the validity of this approach. I. Introduction T HIS work addresses the need for an improved control-oriented model of a dual-mode ramjet/scramjet propulsion system. Improvements are needed to include more realistic estimates of the losses of the propulsion efficiency due to shock wave interactions in the inlet, as well as due to gas dissociation and incomplete combustion in the combustor section. One problem is that previous lowerorder propulsion models [1–3] do not include the losses due to multiple shock interactions, gas dissociation, and incomplete combustioncausedby finiteratechemistry.Thisisaseriousproblem, because the main advantage of ascramjet engine over a ramjet isthat the scramjet reduces losses due to internal shock waves and gas dissociation [4]. That is, the scramjet eliminates the need for strong internalshockwavestodeceleratethegastosubsonicconditionsand maintains lower static temperatures than a ramjet, which reduces the dissociation losses. The present effort addresses previous shortcomings by including both of these types of losses into a code called MASIV. MASIV consists of several reduced-order models (ROMs). One is an inlet ROM that computes losses due to multiple shock/ expansion wave interactions; this ROM is described elsewhere [5]. The other is a fuel/air mixing/combustion ROM that is the focus of the present paper. MASIV has been incorporated into a larger hypersonic vehicle (HSV) code, which is available without charge and without International Traffic in Arms Regulations restrictions. Sincecomputational fluiddynamics(CFD)codestakemanyhours to reach solutions for reacting flows, they are difficult to apply to problems in which a large number of solutions are required. A tool that can solve these configurations in a short time to acceptable accuracyishighlydesirableforcontrolanddesignapplications,such

Preliminary Design Methodology for Hypersonic Engine Flowpaths

A new scramjet engine model, called MASIV, has been developed for control-oriented applications. To reduce computational time, each component models the pertinent physical mechanisms while reducing the spatial dimensionality of the problem. New aspects of MASIV include real-gas dissociation, finite-rate chemistry, a new fuel-air mixing model, an assumed-PDF turbulent combustion model, and interactions of shocks and expansion waves. Strategies for designing 2D scramjet inlets are discussed. One approach is optimize an inlet for a single flight condition. When an inlet designed in this way is at the design condition, all shocks intersect at the cowl leading edge. This optimizes performance at the design condition, but for o-design operation losses are highly sensitive to changes in Mach number and angle of attack. An improved inlet design is described that operates eciently over a range of conditions. In addition, the scramjet combustor also is analyzed to show the eect of pressure distribution on thrust performance for five fuel injection locations. Results suggest general design guidelines, one of which is that injectors should be placed as far upstream as is practical, so that most of the combustion is completed upstream of the nozzle.

Experimental and Numerical Evaluation of Pressure Gain Combustion in a Rotating Detonation Engine

The detonation structure, pressure gain, and thrust production in a rotating detonation engine (RDE) are studied using a combination of experimental and numerical approaches. High frequency time-dependent and low frequency time-averaged static pressure and thrust measurements are acquired for a range of operating conditions and geometry configurations. Acoustic coupling between the detonation channel and air plenum is important for low air mass flow rates and large air injection slots based on analyses of the pressure measurements in the time and frequency domains. The static pressure increases across the air inlet by up to approximately 15% when utilizing a large air injection slot. The pressure increase across the air inlet demonstrates encouraging progress towards realizing pressure gain combustion in RDEs with corresponding challenges associated with isolating the inlet plenums. The time-dependent pressure measurements acquired using a semi-infinite tube arrangement and time-averaged pressure measurements acquired using a capillary tube attenuated arrangement agree to within 30% depending upon location. Quantification of the similarities and differences between the two techniques represents important progress towards acquiring quantitative time-dependent pressure measurements in the challenging environment presented by RDEs. Twodimensional simulations of the RDE capture the essential features of the flow field such as the detonation wave height and angle, trailing edge oblique shock wave, shear layer between the freshly and previously detonated products, and deflagration between the fuel fill region and expansion region containing detonated products. The presence of air purging from the plenum to the channel behind the detonation wave is suggested by the comparison of measured and simulated channel pressure distributions. The pressure, thrust, and wave speed measurements provide benchmark data that are useful for evaluating low and high fidelity simulations of RDEs and improving fundamental understanding of the critical design parameters that influence RDE operation and performance.

Mechanics of Combustion Mode Transition in a Direct-Connect Ramjet–Scramjet Experiment

Combustion mode transitions triggered through active fuel actuation and passive wall heating have been examined in a direct-connect dual-mode combustor experiment. Nonallowable flow configurations are identified through the comparison of the experimental results with an isolator impulse flow theory. These nonallowable configurations consist of three types: those that are facility loss limited, those that are associated with negative entropy generation, and those that fall outside the bounds of the normal shock compression limit. A second law of thermodynamics analysis of the isolator impulse theory and the experimental observations support these results, with the three sets of nonallowed flow configurations presented in terms of both the impulse theory and an experimentally determined operating point analysis of the device. The unstable transition from scramjet to ramjet operation was also noted during the wall heating triggered combustion mode transitions, for particular fueling and inlet flow conditions...

Experimental Ignition Characteristics of a Rotating Detonation Engine under Backpressured Conditions

The ignition of rotating detonation engines is a key aspect to their successful integration into propulsion systems. In this work the effects of mixing scheme, mass flow rate and pre-ignition detonation channel pressure is examined using a throttled ejector test-section. The effective propellant mixing, as measured by the required pre-detonation cell-width, is found to vary over a range of values from 0.2 to 1.0, dependent on the injection geometry considered. The different physical configurations are tested for equivalence ratios of 0.7 to 1.0 and air injector to detonation channel area ratios from 0.23 to 0.43. The transition from steady pre-detonation to steady post-detonation fuel-jet environments is also discussed.

Overview of Performance, Application, and Analysis of Rotating Detonation Engine Technologies

Recent accomplishments related to the performance, application, and analysis of rotating detonation engine technologies are discussed. The pioneering development of optically accessible rotating detonation engines coupled with the application of established diagnostic techniques is enabling a new research direction. In particular, OH* chemiluminescence images of detonations propagating through the annular channel of a rotating detonation engine are reported and appear remarkably similar to computational fluid dynamic results of rotating detonation engines published in the literature. Specific impulse measurements of rotating detonation engines and pulsed detonation engines are shown to be quantitatively similar for engines operating on hydrogen/air and ethylene/air mixtures. The encouraging results indicate that rotating detonation engines are capable of producing thrust with fuel efficiencies that are similar to those associated with pulsed detonation engines while operating on gaseous hydrocarbon fuels....

Comparison of Numerically Simulated and Experimentally Measured Performance of a Rotating Detonation Engine

Abstract A quasi-two-dimensional, computational fluid dynamic (CFD) simulation of a rotating detonation engine (RDE) is described. The simulation operates in the detonation frame of reference and utilizes a relatively coarse grid such that only the essential primary flow field structure is captured. This construction and other simplifications yield Grapidly converging, steady solutions. Viscous effects, and heat transfer effects are modeled using source terms. The effects of potential inlet flow reversals are modeled using boundary conditions. Results from the simulation are compared to measured data from an experimental RDE rig with a convergingdiverging nozzle -added. The comparison is favorable for the two operating points examined. The uti lity of the code as a performance optimization tool and a diagnostic tool are discussed. Nomenclature a nondimensional speed of sound a * reference speed of sound, 1250 ft/s f air to fuel ratio (by mass) g c Newton constant, 32.174 ft-lb m /lb