Derek J. Dalle

New Method for Computing Performance of Choked Reacting Flows and Ram-to-Scram Transition

An improved method has been developed to compute the thrust of a dual-mode scramjet, which is an engine with a combustor that operates both subsonically and supersonically. This strategy applies to any internal flow that can be modeled one-dimensionally. To handle the mathematical singularity at the location of thermal choking, the simple Shapiro method is expanded to create a new method that includes finite-rate chemistry and high-temperature gas properties. A forward shooting method is employed to find appropriate initial conditions for integration of the governing equations, which results in a unique transonic (choked) condition capable of reaching a supersonic state at the end of the domain. Solutions of the governing equations are computed using the propulsion code MASIV, which has been integrated into a hypersonic vehicle flight dynamics code. Computations for both ram-mode and scram-mode operations are compared to experimental results. Predictions are made for flight conditions of a hypersonic vehi...

Uncertainty Propagation in Integrated Airframe–Propulsion System Analysis for Hypersonic Vehicles

Air-breathing hypersonic vehicles are based on an airframe-integrated scramjet engine. The elongated forebody that serves as the inlet of the engine is subject to harsh aerothermodynamic loading, which causes it to deform. Unpredicted deformations may produce unstart, combustor chocking, or structural failure due to increased loads. An uncertainty quantification framework is used to propagate the effects of aerothermoelastic deformations on the performance of the scramjet engine. A loosely coupled airframe-integrated scramjet engine is considered. The aerothermoelastic deformations calculated for an assumed trajectory and angle of attack are transferred to a scramjet engine analysis. Uncertainty associated with deformation prediction is propagated through the engine performance analysis. The effects of aerodynamic heating and aerothermoelastic deformations at the cowl of the inlet are the most significant. The cowl deformation is the main contributor to the sensitivity of the propulsion system performance...

Hypersonic Vehicle Thrust Sensitivity to Angle of Attack and Mach Number

A new control-oriented scramjet engine model has been developed, named the MichiganAFRL Scramjet In Vehicle model (MASIV); it is used to compute thrust sensitivity to variation in flight conditions. The model solves conservation equations in 1-D, using several modeling techniques to retain some of the fidelity of higher-order simulations. A number complex physical processes are modeled (including jet mixing and finite rate chemistry) by a combination of ordinary dierential equations and algebraic scaling laws. The axial evolutions of the various flow quantities are computed in a short time, relative to computational fluid dynamics solutions. Although there is some loss of accuracy when using Reduced Order Models (ROMs), MASIV computes the overall performance of the flow path with respect to vehicle dynamics (thrust and drag) at an acceptable level for preliminary design and for use as a submodel for control design and evaluation. The model is exercised to predict the sensitivity of the thrust to variations in Mach number and angle of attack, and to compute the operating envelope of the engine.

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.

Scramjet Engine Model MASIV: Role of Mixing, Chemistry and Wave Interaction

This paper provides details of the combustion and inlet submodels used in the MichiganAir Force Scramjet In Vehicle (MASIV) model. The model solves conservation equations in 1-D, using several modeling techniques to retain some of the fidelity of higher-order simulations. Inlet wave interactions, fuel mixing and finite-rate chemistry are considered. The order of the problem is reduced by physics-based, experimentally-verified algebraic scaling laws, which retains the required physics but reduces the computation time of the problem to seconds, instead of the several days required by computational fluid dynamics (CFD). Scaling coecients and assumptions are given. The model is used to compute the performance of an experimental configuration for which real data are available.

Ascent Trajectories of Hypersonic Aircraft: Operability Limits Due to Engine Unstart

A generic waverider-type hypersonic aircraft that undergoes an ascent trajectory has been modeled using a first-principles reduced-order model. Two types of operability limits are added that represent boundaries on the aircraft trajectory map (of vehicle altitude versus Mach number). These boundaries are associated with engine unstart and ram–scram transition. The predicted unstart boundary is to be avoided; the ram–scram transition is a condition through which the aircraft must fly, but it is useful for the control system to know when this transition is approached to account for possible sudden changes in thrust and moments. The model shows that unstart occurs if the aircraft flies too high, too slow, or at too great of an acceleration. The unstart limit can be avoided by selecting a trajectory having sufficiently large dynamic pressure or a low vehicle acceleration. Optimizing these factors avoids an excessive value of the fuel–air ratio that is required for trim. The model also identifies an engine inl...

Performance Analysis of Variable-Geometry Scramjet Inlets Using a Low-Order Model

Scramjet vehicles, especially those used as part of an orbital launch system, must operate over a wide range of flight conditions. One component that has difficulty accommodating a range of Mach numbers is the inlet. In this article, only two-dimensional-type scramjet inlets are considered. Such an inlet with fixed geometry can be designed for a single Mach number (using approximately the shock-on-lip configuration) or a range of Mach numbers. However, the performance of the inlet tends to degrade as the size of the Mach number range increases. One method to improve this performance is to use a variable-geometry cowl. Three cowl motions are considered in this paper: moving the whole cowl up and down, moving the whole cowl forward and backward, and rotating the cowl lip. A low-order model designed for control-oriented applications is used to simulate wave interactions. The model is used to evaluate the benefits of each type of variable geometry, and an inlet designed for a wide range of Mach numbers is presented.

Hypersonic Vehicle Flight Dynamics with Coupled Aerodynamics and Reduced-order Propulsive Models

A new model is developed to more accurately capture the dynamics and control of an air-breathing hypersonic vehicle using a computationally inexpensive formulation. The vehicle model integrates a scramjet engine analysis tool developed specifically for use in a control-oriented model and a six-degree-of-freedom rigid-body flight dynamics model. The combined hypersonic vehicle model requires less than ten seconds with a single 2.6 GHz processor to calculate the total thrust, lift, and aerodynamic moment on the vehicle. The inlet and nozzle analysis handles shock-shock and shock-expansion interactions, and expansions are considered to be a series of discrete waves. The combustor model utilizes scaling laws that retain some of the fidelity of higher-order simulations. On the parts of the vehicle that are not part of the propulsive flowpath, modified shock-expansion theory is used to calculate the pressure. In this approach the role of the propulsive model will be only to calculate the net forces and moments on the inlet, combustor, and nozzle. The result is a control-oriented hypersonic vehicle model that qualitatively captures the nonlinear interactions between vehicle dynamics and the scramjet engine.

Minimum-Fuel Ascent of a Hypersonic Vehicle Using Surrogate Optimization

A general strategy is identified to compute the minimum fuel required for the ascent of a generic hypersonic vehicle that is propelled by a dual-mode ramjet–scramjet engine with hydrogen fuel. The study addresses the ascent of an accelerator vehicle rather than a high-speed cruiser. Two general types of ascent trajectories are considered: acceleration within scramjet mode, and acceleration across the ramjet–scramjet transition boundary maximum acceleration and maximum dynamic pressure (lowest allowed altitude) were shown to be near optimum for scramjet-mode trajectories, but optimized trajectories were found to be more complex when both modes are considered. The first-principles model used in this paper computes the combustion efficiency using finite-rate chemistry and a fuel–air mixing model. It also computes the inlet efficiency with a shock wave interaction code, and thus avoids empirical formulas for efficiency that were used in previous models.

Flight envelope calculation of a hypersonic vehicle using a first principles-derived model

Steady, level flight for an air-breathing hypersonic vehicles requires balancing intricate couplings among the engine, lifting surfaces, and control effectors. A newly developed fundamental model is used to determine the range of flight Mach numbers and altitudes at which this balance can be obtained. The hypersonic vehicle was developed specifically for flight dynamics evaluations, and the model can calculate the net forces and moments on a three-dimensional vehicle in less than ten seconds using a single 2.6 GHz processor. The propulsive model includes complex physics such as wave interactions, fuel mixing, and finite-rate chemistry. This type of model requires less computational resources than a model based on computational fluid dynamics and provides a more accurate characterization of the flight envelope than simplified models could.