Jose A. Camberos

Characterization of Aerospace Vehicle Performance and Mission Analysis Using Thermodynamic Availability

The fundamental relationship between entropy and aerospace vehicle and mission performance is analyzed in terms of the general availability rate balance between force-based vehicle performance, available energy associated with expended propellant, and the overall loss rate of availability, including the vehicle wake. The availability relationship for a vehicle is analytically combined with the vehicle equations of motion; this combination yields the balance between on-board energy rate usage and rates of changes in kinetic and potential energies of the vehicle and overall rate of entropy production. This result is then integrated over time for a general aerospace mission; as examples, simplified single-stage-to-orbit rocket-powered and air-breathing missions are analyzed. Examination of rate of availability loss for the general case of an accelerating, climbing aerospace vehicle provides a powerful loss superposition principle in terms of the separate evaluation and combination of loss rates for the same vehicle in cruise, acceleration, and climb. Rate of availability losses is also examined in terms of separable losses associated with the propulsion system and external aerodynamics. These loss terms are cast in terms of conventional parameters such as drag coefficient and engine specific impulse. Finally, rate losses in availability for classes of vehicles are described.

Benefits of Exergy-Based Analysis for Aerospace Engineering Applications—Part I

This paper compares the analysis of systems from two different perspectives: an energy-based focus and an exergy-based focus. A complex system was simply modeled as interacting thermodynamic systems to illustrate the differences in analysis methodologies and results. The energy-based analysis had combinations of calculated states that are infeasible. On the other hand, the exergy-based analyses only allow feasible states. More importantly, the exergy-based analyses provide clearer insight to the combination of operating conditions for optimum system-level performance. The results strongly suggest changing the analysis/design paradigm used in aerospace engineering from energy-based to exergy-based. This methodology shift is even more critical in exploratory research and development where previous experience may not be available to provide guidance. Although the models used herein may appear simplistic, the message is very powerful and extensible to higher-fidelity models: the 1st Law is only a necessary condition for design, whereas the 1st and 2nd Laws provide the sufficiency condition.

Mission-Integrated Exergy Analysis for Hypersonic Vehicles: Methodology and Application

Recently developed theoretical work in which energy (the first law of thermodynamics) and entropy (the second law of thermodynamics) considerations are consistently applied to aerospace vehicles is used to provide a detailed exergy (availability) and performance analysis for an airbreathing hypersonic vehicle. An acceleration and climb mission at constant freestream dynamic pressure is performed with detailed instantaneous and time-integrated audits of entropy generation in and over the vehicle and in the vehicle wake. Entropy generation in the vehicle wake ranges from five to eight times the total entropy generation in and over the vehicle. The impact of irreversibility occurring in and over the vehicle itself on the total entropy generation in the wake is a small fraction of the overall wake losses. Fifteen percent of the overall energy input during the mission actually goes into productive acceleration and climb. The remainder is associated with the generation of entropy due to irreversibility in and o...

Flowfield Uncertainty Analysis for Hypersonic CFD Simulations

Uncertainty quantification (UQ) in the hypersonic flow regime offers valuable information to determine physical models in need of improvement and to assist in design of vehicles and flight experiments. Here we present results of UQ analysis based on polynomial chaos method to determine flowfield and surface heat flux uncertainty under typical blunt-body re-entry conditions. The NASA Langley code, LAURA, was used for axisymmetric CFD calculations of chemically reacting hypersonic flow over FIRE-II configuration. A third order polynomial chaos (PC) method using the Gauss-Hermite quadrature was applied for determining probability density functions and moments of output quantities. Input parameters such as freestream density, velocity, and temperature were varied and the propagation of their corresponding uncertainties on output properties of interest through the flowfield were studied. An order of magnitude increase in surface heat flux uncertainties was observed for an input freestream velocity uncertainty of ±100 ft/s, or 0.29%. This parameter thus has the greatest sensitivity to variations, and conversely the freestream temperature has the least sensitivity. Nomenclature Hn Hermite polynomial of order n j number of collocation points per dimension k order of PC expansion n order of accuracy for PC and Hermite polynomials N number of samples P total number of points in PC expansion ˙ q heat flux (kW/m 2 ) T translational temperature (K) V velocity (m/s) w weight corresponding to abscissa x input parameter value Y output value from solver ¯ Y mean output value � uncertainty ξ Gaussian random variable μ mean ρ density (kg/m 3 )

Systems Engineering in Terms of Exergy

We address the design of a flight vehicle from the viewpoint of a system of systems and we discuss the integration of the individual technical disciplines. Then a conceptual fundamental methodology and tools required for the analysis, design, and optimization of aerospace vehicles in terms of the efficient use of on-board energy are discussed. This suggests changing the design paradigm to the optimization of a system of energy systems. We propose a foundation for system-level design with optimization based on minimum exergy destruction.

Induced Drag Minimization with Optimal Scheduling of Virtual Surface Deflection Boundary Conditions

This project took an initial step towards our goal of implementing multiple trailing edge “virtual flaps” to control the span-wise lift distribution over a finite wing for minimizing lift–induced drag. The first part of this project compared Computational Fluid Dynamic (CFD) results of an untwisted, finite rectangular wing (NACA 0006, AR = 40/6) using no flap deflections against theoretical results for verification of the methodology. A lifting line code handled the theoretical computations as well as comparison of the results. Dividing the wing into twenty span-wise sections and using a surface integral of pressure at each section provided a method from which to extract a span-wise lift distribution from the CFD solution. A comparison of the numerical and theoretical lift distributions, under flow conditions representing Mach 0.3 – 0.7 subsonic and transonic flows at small angle of attack, shows good agreement with an average error of 2.4% over the wingspan. An important part of the methodology required extracting accurate and robust calculations of induced drag from the CFD solutions. Inaccuracies associated with the (standard) surface integral method of calculating drag prompted the use of a wake integral method. To minimize grid requirements and complexity associated with fully viscous solutions, the CFD solution focused on the Euler equations and only the induced drag obtained. Successful implementation of a wake integral method via a Trefftz-plane analysis provided an approximation of the induced drag, which seemed to prove more accurate than the surface integral method.

Analysis of Power Losses and Wake Entropy Production for Hypersonic Flight Vehicles

We examine the governing relationships between forces experienced by a vehicle, vehicle power usage, losses and entropy production. Vehicle wake losses (like losses associated with the vehicle itself) are shown to be directly related to lost force power increments on the vehicle. Conventional exergy (or availability) methodology without explicit consideration of the wake and, specifically, without consideration of vehicle flow-field/wake entropy relationships, is shown to be problematic for accurate assessment of losses. The methodology is then re-formulated with explicit consideration of the vehicle/wake entropy relationship. Lost power increments are derived, hence allowing the detailed analysis/auditing of vehicle performance. This methodology is rigorously related throughout its entire development to the concept of wake entropy production and the important impact of vehicle entropy production and characteristics on the wake entropy production. The fundamental thermodynamic linkages and relationships between force, entropy, and power for an individual streamtube are examined. These analytical results are then expanded to entire flow-fields characteristic of vehicles in flight (multiple streamtubes in and over vehicle surfaces and downstream wake equilibration of those streamtubes) in order to unify explicit force-based methodology and the entropy method. The ongoing research represented by this and previous work should ultimately enable the integration of all vehicle subsystems (not just aerodynamic and propulsive subsystems) using a synergistic currency for analysis, design, and, ultimately, optimization of aerospace vehicles.

Statistical, Modular Systems Integration Using Combined Energy & Exergy Concepts

This paper details statistical concepts to systems-level applications with relevance to integration, operation, and optimization of engineering components and systems. A physicsbased exergy analysis is combined with system performance goals. Designed experiments are used to pre-determine relevant simulation points for the analysis in order to develop the statistical models most effectively and efficiently. The results of the simulation are then processed via advanced statistics to create a surrogate model that identifies the component and/or system within desired or anticipated operational ranges. These statistical surrogate models represent the system in a modular fashion. In this manner, a statistical module may be interfaced independently from its origination and a “system of systems” may be built from the surrogate modules that may be used to efficiently investigate engineering trades and perform preliminary design studies. Quantitative examples from aerospace components and systems are used to demonstrate the overall process.

Exergy Based Design Methodology for Airfoil Shape Optimization and Wing Analysis

As modern aircraft wings have evolved, the structural designs of aircraft wings have adopted a variety of mechanical systems for aerodynamic control, including flaps, slats, ailerons, and spoilers. Wings also have become fuel tanks, antennae, and payload carriers, in addition to generating lift. Wings have continued to evolve geometrically by incorporating taper, winglets, and sweep to improve aerodynamic efficiency. In the second century of flight, adaptive-surface flow control and conformal morphing are technologies that will be further incorporated into wing design. The integration of adaptive control surfaces into aircraft designs will allow wings to actively respond to their environment. Whether the airplane is taking off, ascending, cruising, descending, loitering, or landing, this technology will allow a wing to tailor its shape to achieve optimal flight conditions. Our interest lies in the potential use of exergy-based strategies for aircraft systems integration and design. The approach focuses on the useful component of energy (i.e., exergy) necessary to operate the system. Because energy is required for the functioning of any system, exergy naturally becomes a common currency for comparing multisystem designs. According to the second law of thermodynamics, exergy is not conserved during any real process. It is consumed to meet system objectives, but in doing so, some is irreversibly destroyed. This destruction represents a real cost for executing the process. The destruction of exergy is proportional to the corresponding entropy generation. So, minimizing entropy generation leads to a better use of exergy. That is why entropy generation minimization (EGM) methods have been used for many thermodynamic optimization problems. At the heart of exergy-based systems integration are the analytical methods used to characterize each system and to optimize within and between systems. Within this chapter, we will examine methods that optimize 2-D airfoil shapes

An Advanced Exergy and Energy Simulation Tool for Large-Scale Design/Optimization of Aerospace Systems

This paper discussed procedures developed for the design/optimization of large-scale aerospace systems; using the iterative local global optimization (ILGO) – procedure. The ILGO procedure obviates the need for nested optimization loops in the design of a complex system decomposed into several subsystems. A new object-based scripting tool is developed and used to analyze an advanced tactical fighter with an exergy-based objective. The results are compared with those obtained using a weight-based objective.