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Technical Paper

A Dynamic Two-Phase Component Model Library for High Heat Flux Applications

2019-03-19
2019-01-1386
Pumped two-phase systems using mini or microchannel heat sink evaporators are prime candidates for high heat flux applications due to relatively low pumping power requirements and efficient heat removal in compact designs. A number of challenges exist in the implementation of these systems including: ensuring subcooled liquid to the pump to avoid cavitation, avoiding dry out conditions in heat exchangers that can lead to failures of the components under cooling, and avoiding flow instabilities that can damage components in an integrated system. To reduce risk and cost, modeling and simulation can be employed in the design and development of these complex systems, but such modeling must include the relevant behavior necessary to capture the above dynamic effects.
Technical Paper

A Multi-Domain Component Based Modeling Toolset for Dynamic Integrated Power and Thermal System Modeling

2019-03-19
2019-01-1385
Design of modern aircraft relies heavily on modeling and simulation for reducing cost and improving performance. However, the complexity of aircraft architectures requires accurate modeling of dynamic components across many subsystems. Integrated power and thermal modeling necessitates dynamic simulations of liquid, air, and two-phase fluids within vapor cycle system components, air cycle machine and propulsion components, hydraulic components, and more while heat generation of many on-board electrical components must also be precisely calculated as well. Integration of these highly complex subsystems may result in simulations which are too computationally expensive for quickly modeling extensive variations of aircraft architecture, or will require simulations with reduced accuracy in order to provide computationally inexpensive models.
Technical Paper

Risk Assessment of Fuel Property Variability Using Quasi-Random Sampling/Design of Experiments Methodologies

2019-03-19
2019-01-1387
Increases in on-board heat generation in modern military aircraft have led to a reliance on thermal management techniques using fuel as a primary heat sink. However, recent studies have found that fuel properties, such as specific heat, can vary greatly between batches, affecting the amount of heat delivered to the fuel. With modern aircraft systems utilizing the majority of available heat sink capacity, an improved understanding of the effects of fuel property variability on overall system response is important. One way to determine whether property variability inside a thermal system causes failure is to perform uncertainty analyses on fuel thermophysical properties and compare results to a risk assessment metric. A sensitivity analysis can be performed on any properties that cause inherent system variability to determine which properties contribute the most significant impact.
Journal Article

Electric versus Hydraulic Flight Controls: Assessing Power Consumption and Waste Heat Using Stochastic System Methods

2017-09-19
2017-01-2036
Of all aircraft power and thermal loads, flight controls can be the most challenging to quantify because they are highly variable. Unlike constant or impulsive loads, actuator power demands more closely resemble random processes. Some inherent nonlinearities complicate this even further. Actuation power consumption and waste heat generation are both sensitive to input history. But control activity varies considerably with mission segment, turbulence and vehicle state. Flight control is a major power consumer at times, so quantifying power demand and waste heat is important for sizing power and thermal management system components. However, many designers sidestep the stochastic aspects of the problem initially, leading to overly conservative system sizing. The overdesign becomes apparent only after detailed flight simulations become available. These considerations are particularly relevant in trade studies comparing electric versus hydraulic actuation.
Journal Article

A Specification Analysis Framework for Aircraft Systems

2016-09-20
2016-01-2023
Future aircraft systems are projected to have order of magnitude greater power and thermal demands, along with tighter constraints on the performance of the power and thermal management subsystems. This trend has led to the need for a fully integrated design process where power and thermal systems, and their interactions, are considered simultaneously. To support this new design paradigm, a general framework for codifying and checking specifications and requirements is presented. This framework is domain independent and can be used to translate requirement language into a structured definition that can be quickly queried and applied to simulation and measurement data. It is constructed by generalizing a previously developed power quality analysis framework. The application of this framework is demonstrated through the translation of thermal specifications for airborne electrical equipment, into the SPecification And Requirement Evaluation (SPARE) Tool.
Journal Article

Integrated Power and Thermal Management System (IPTMS) Demonstration Including Preliminary Results of Rapid Dynamic Loading and Load Shedding at High Power

2015-09-15
2015-01-2416
An IPTMS hardware facility has been established in the laboratories of the Aerospace Systems Directorate of the Air Force Research Laboratory (AFRL) at Wright-Paterson Air Force Base (WPAFB). This hardware capability was established to analyze the transient behavior of a high power Electrical Power System (EPS) coupled virtually to a Thermal Management System (TMS) under fast dynamic loading conditions. The system incorporates the use of dynamic electrical load, engine emulation, energy storage, and emulated thermal loads operated to investigate dynamics under step load conditions. Hardware architecture and control options for the IPTMS are discussed. This paper summarizes the IPTMS laboratory demonstration system, its capabilities, and preliminary test results.
Technical Paper

Development and Performance of a Reduced Order Dynamic Aircraft Model

2015-09-15
2015-01-2415
A reduced order dynamic aircraft model has been created for the purpose of enabling constructive simulation studies involving integrated thermal management subsystems. Such studies are motivated by the increasing impact of on-board power and thermal subsystems to the overall performance and mission effectiveness of modern aircraft. Previous higher-order models that have been used for this purpose have the drawbacks of much higher development time, along with much higher execution times in the simulation studies. The new formulation allows for climbs, accelerations and turns without incurring computationally expensive stability considerations; a dynamic inversion control law provides tracking of user-specified mission data. To assess the trade-off of improved run-time performance against model capability, the reduced order formulation is compared to a traditional six degree-of-freedom model of the same air vehicle.
Technical Paper

Rapid Access to High-Resolution Thermal/Fluid Component Modeling

2012-10-22
2012-01-2170
Although computational fluid dynamics (CFD) simulations have been widely used to successfully resolve turbulence and boundary layer phenomena induced by microscale flow passages in advanced heat exchanger concepts, the expense of such simulations precludes their use within system-level models. However, the effect of component design changes on systems must be better understood in order to optimize designs with little thermal margin, and CFD simulations greatly enhance this understanding. A method is presented to introduce high resolution, 3-D conjugate CFD calculations of candidate heat exchanger cores into dynamic aerospace subsystem models. The significant parameters guiding performance of these heat exchangers are identified and a database of CFD solutions is built to capture steady and unsteady performance of microstructured heat exchanger cores as a function of the identified parameters and flow conditions.
Journal Article

A Hybrid Economy Bleed, Electric Drive Adaptive Power and Thermal Management System for More Electric Aircraft

2010-11-02
2010-01-1786
Minimizing energy use on more electric aircraft (MEA) requires examining in detail the important decision of whether and when to use engine bleed air, ram air, electric, hydraulic, or other sources of power. Further, due to the large variance in mission segments, it is unlikely that a single energy source is the most efficient over an entire mission. Thus, hybrid combinations of sources must be considered. An important system in an advanced MEA is the adaptive power and thermal management system (APTMS), which is designed to provide main engine start, auxiliary and emergency power, and vehicle thermal management including environmental cooling. Additionally, peak and regenerative power management capabilities can be achieved with appropriate control. The APTMS is intended to be adaptive, adjusting its operation in order to serve its function in the most efficient and least costly way to the aircraft as a whole.
Technical Paper

Power Thermal Management System Design for Enhanced Performance in an Aircraft Vehicle

2010-11-02
2010-01-1805
The thermal management of modern aircraft has become more challenging as aircraft capabilities have increased. The use of thermally resistant composite skins and the desire for low observability, reduced ram inlet size and number, have reduced the ability to transfer heat generated by the aircraft to the environment. As the ability to remove heat from modern aircraft has decreased, the heat loads associated with the aircraft have increased. Early in the aircraft design cycle uncertainty exists in both aircraft requirements and simulation predictions. In order to mitigate the uncertainty, it is advantageous to design thermal management systems that are insensitive to design cycle uncertainty. The risk associated with design uncertainty can be reduced through robust optimization. In the robust optimization of the thermal management system, three noise factors were selected: 1) engine fan air temperature, 2) avionics thermal load, and 3) engine thrust.
Technical Paper

A Reduced-Order Enclosure Radiation Modeling Technique for Aircraft Actuators

2010-11-02
2010-01-1741
Modern aircraft are aerodynamically designed at the edge of flight stability and therefore require high-response-rate flight control surfaces to maintain flight safety. In addition, to minimize weight and eliminate aircraft thermal cooling requirements, the actuator systems have increased power-density and utilize high-temperature components. This coupled with the wide operating temperature regimes experienced over a mission profile may result in detrimental performance of the actuator systems. Understanding the performance capabilities and power draw requirements as a function of temperature is essential in properly sizing and optimizing an aircraft platform. Under the Air Force Research Laboratory's (AFRL's) Integrated Vehicle and Energy Technology (INVENT) Program, detailed models of high performance electromechanical actuators (HPEAS) were developed and include temperature dependent effects in the electrical and mechanical actuator components.
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