David J. Moorhouse

Proposed System-Level Multidisciplinary Analysis Technique Based on Exergy Methods

It is suggested that it may be time to consider whether we have reached a plateau in terms of the evolutionary nature of e ight vehicle design and optimization. For a time, progress was measured in terms of maximum speed, which is a straightforward metric when the next design is evolved from the preceding model. There are times, however, when we need to depart from the evolutionary process and create a breakthrough design. The question to be asked is whether there is any way to dee ne system-level analysis and optimization techniques to facilitate the vehicle design process with a more global measure of effectiveness. This paper presents such a methodology for the design of the complete integrated system of systems. Work that has been done in energy-based methods is briee y reviewed, sinceenergy is an implicit consideration in many aerospace disciplines. In addition, methods such as exergy and thermoeconomics have been applied in the design of ground power stations and they are currently being studied for application to aircraft subsystems. The objective of this paperis to expand exergy methods to the design of a complete e ight vehicle by dee ning mission requirements as an exergy/work problem cascading down to each component in the same framework. This paper also serves to introduce a special section of this journal devoted to the application of exergy methods to all levels of e ight vehicle design. Overall, the proposed technique provides a method to facilitate system-level optimization at all levels of the design process.

Benefits and design challenges of adaptive structures for morphing aircraft

The purpose of this paper is to discuss the future of adaptive structures leading towards the concept of a fully morphing aircraft configuration. First, examples are shown to illustrate the potential system-level mission benefits of morphing wing geometry. The challenges of design integration are discussed along with the question of how to address the optimisation of such a system. This leads to a suggestion that non-traditional methods need to be developed. It is suggested that an integrated approach to defining the work to be done and the energy to be used is the solution. This approach is introduced and then some challenges are examined in more detail. First, concepts of mechanisation are discussed as ways to achieve optimum geometries. Then there are discussions of non-linearities that could be important. Finally, the flight control design challenge is considered in terms of the rate of change of the morphing geometry. The paper concludes with recommendations for future work.

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.

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.

Designed Experiments: Statistical Approach to Energy- and Exergy-Based Optimization

We extend the energy and exergy-based methodology presented in previous work 1,2 from analysis to preliminary design. Therein, a three-component system was modeled in which heat transfer from the energy source was allowed, while the other devices were considered to be reversible. Those single-parameter studies yielded many results which were physically impossible, clearly suggesting that the analysis/design paradigm be changed from energybased to exergy-based. Here, we extend the analysis to preliminary design applications. A steam turbine with fixed inlet conditions was modeled thermodynamically and simulated in MATLAB using three design variables: turbine exit quality, turbine exit pressure, and turbine heat transfer. A statistically generated test matrix was developed using Design of Experiments (DOE) for three test cases. For the first test case, only the quality was varied while exit pressure and heat transfer remained constant. For the second test case, both quality and exit pressure were varied while heat transfer remained constant. The last case allowed all three design variables to vary simultaneously. The test matrix was analyzed using a 1 st Law as well as combined 1 st and 2 nd Law methodology to determine turbine specific work and exergy destruction for the system. Results from the test cases were analyzed to generate surrogate models used for turbine optimization.

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.

Quantifying Irreversible Losses for Magnetohydrodynamic Flow Analysis and Design Integration.

The evolutionary nature of flight-vehicle design and optimization has served technological demands well in order to reach the performance of current aircraft. At times, however, we must depart from the evolutionary process and aim for a breakthrough design. The design of plasma-assisted aerospace vehicles challenges traditional experience and databases. To meet this challenge, the authors propose incorporating the second law of thermodynamics into generalized analysis and design methods based on the concept of exergy. First, the development of the appropriate equations for magnetohydrodynamic (MHD) fluid flow are reviewed and summarized. The MHD equations are then supplemented with the entropy- and exergy-balance equations. Then a design framework based on the exergy considerations is presented. Of particular interest to the authors is application of entropy/exergy and the second-law principle in the analysis and design of complex physical systems. We focus on the incorporation of the entropy-generation formula and, by direct correspondence, the exergy-balance equations consistent with compressible MHD fluid flow

Common Currency for System Integration of High Intensity Energy Subsystems

Aerospace vehicle design has progressed in an evolutionary manner, with certain discrete changes such as turbine engines replacing propellers for higher speeds. The evolution has worked very well for commercial aircraft because the major components can be optimized independently. This is not true for many military configurations which require a more integrated approach. In addition, the introduction of aspects for which there is no pre-existing database requires special attention. Examples of subsystem that have no pre-existing data base include directed energy weapons (DEW) such as high power microwaves (HPM) and high energy lasers (HEL). These devices are inefficient, therefore a large portion of the energy required to operate the device is converted to waste heat and must be transferred to a suitable heat sink. For HPM, the average heat load during one ‘shot’ is on the same order as traditional subsystems and thus designing a thermal management system is possible. The challenge is transferring the heat from the HPM device to a heat sink. The power density of each shot could be hundreds of megawatts. This heat must be transferred from the HPM beam dump to a sink. The heat transfer must occur at a rate that will support shots in the 10–100Hz range. For HEL systems, in addition to the high intensity, there are substantial system level thermal loads required to provide an ‘infinite magazine.’ Present models are inadequate to analyze these problems, current systems are unable to sustain the energy dissipation required and the high intensity heat fluxes applied over a very short duration phenomenon is not well understood. These are examples of potential future vehicle integration challenges. This paper addresses these and other subsystems integration challenges using a common currency for vehicle optimization. Exergy, entropy generation minimization, and energy optimization are examples of methodologies that can enable the creation of energy optimized systems. These approaches allow the manipulation of fundamental equations governing thermodynamics, heat transfer, and fluid mechanics to produce minimized irreversibilities at the vehicle, subsystem and device levels using a common currency. Applying these techniques to design for aircraft system-level energy efficiency would identify not only which subsystems are inefficient but also those that are close to their maximum theoretical efficiency while addressing diverse system interaction and optimal subsystem integration. Such analyses would obviously guide researchers and designers to the areas having the highest payoff and enable departures from the evolutionary process and create a breakthrough design.