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Technical Paper

Yaw Effects on the Narrowband Spectra Above a Delta Wing in Turbulent Flow

Combat aircraft maneuvering at high angles of attack or in landing approach are likely to encounter conditions where the flow over the swept wings is yawed. This paper examines the effect of yaw on the spectra of turbulence above and aft of the wing, in the region where fins and control surfaces are located. Prior work has shown the occurrence of narrowband velocity fluctuations in this region for most combat aircraft models, including those with twin fins. Fin vibration and damage has been traced to excitation by such narrowband fluctuations. The narrowband fluctuations themselves have been traced to the wing surface. The issue in this paper is the effect of yaw on these fluctuations, as well as on the aerodynamic loads on a wing, without including the perturbations due to the airframe.
Technical Paper

Viable Designs Through a Joint Probabilistic Estimation Technique

A key issue in complex systems design is measuring the ‘goodness’ of a design, i.e. finding a criterion through which a particular design is determined to be the ‘best’. Traditional choices in aerospace systems design, such as performance, cost, revenue, reliability, and safety, individually fail to fully capture the life cycle characteristics of the system. Furthermore, current multi-criteria optimization approaches, addressing this problem, rely on deterministic, thus, complete and known information about the system and the environment it is exposed to. In many cases, this information is not be available at the conceptual or preliminary design phases. Hence, critical decisions made in these phases have to draw from only incomplete or uncertain knowledge. One modeling option is to treat this incomplete information probabilistically, accounting for the fact that certain values may be prominent, while the actual value during operation is unknown.
Technical Paper

Transmission Electron Microscopy of Soot Particles sampled directly from a Biodiesel Spray Flame

For better understanding of soot formation and oxidation processes in a biodiesel spray flame, the morphology, microstructure and sizes of soot particles directly sampled in a spray flame fuelled with soy-methyl ester were investigated using transmission electron microscopy (TEM). The soot samples were taken at different axial locations in the spray flame, 40, 50 and 70 mm from injector nozzle, which correspond to soot formation, peak, and oxidation zones, respectively. The biodiesel spray flame was generated in a constant-volume combustion chamber under a diesel-like high pressure and temperature condition (6.7 MPa, 1000K). Density, diameter of primary particles and radius of gyration of soot aggregates reached a peak at 50 mm from the injector nozzle and was lower or smaller in the formation or oxidation zones of the spray.
Journal Article

Transmission Electron Microscopy of Soot Particles Directly Sampled in Diesel Spray Flame - A Comparison between US#2 and Biodiesel Soot

For a better understanding of soot formation and oxidation processes in conventional diesel and biodiesel spray flames, the morphology, microstructure and sizes of soot particles directly sampled in spray flames fuelled with US#2 diesel and soy-methyl ester were investigated using transmission electron microscopy (TEM). The soot samples were taken at 50mm from the injector nozzle, which corresponds to the peak soot location in the spray flames. The spray flames were generated in a constant-volume combustion chamber under a diesel-like high pressure and high temperature condition (6.7MPa, 1000K). Direct sampling permits a more direct assessment of soot as it is formed and oxidized in the flame, as opposed to exhaust PM measurements. Density of sampled soot particles, diameter of primary particles, size (gyration radius) and compactness (fractal dimension) of soot aggregates were analyzed and compared. No analysis of the soot micro-structure was made.
Technical Paper

Tradeoff Study of High Altitude Solar Reflector Concepts

A direct solution to Global Warming would be to reflect a part of sunlight back into Space. A system tradeoff study is being developed with three of the concepts that are being evaluated as long-endurance high-altitude reflectors. The first concept is a high aspect ratio solar powered flying wing towing reflector sheets. This concept is named “Flying Carpet”. Second is a centrifugally stretched high altitude solar reflector (CSHASR). The CSHASR has 4 rotors made of reflector sheets with a hub stretching to 60 percent of the radius, held together by an ultralight quad-rotor structure. Each rotor is powered by a solar-electric motor. A variation on this concept, forced by nighttime descent rate concerns, is powered by tip-mounted solar panels and propellers with some battery storage augmenting rotational inertia as well as energy storage. The third concept is an Aerostatically Balanced Reflector (ABR) sheet, held up by hydrogen balloons.
Technical Paper

Towards Electric Aircraft: Progress under the NASA URETI for Aeropropulsion and Power Technology

The environmental impact of aircraft, specifically in the areas of noise and NOx emissions, has been a growing community concern. Coupled with the increasing cost and diminishing supply of traditional fossil fuels, these concerns have fueled substantial interest in the research and development of alternative power sources for aircraft. In 2003, NASA and the Department of Defense awarded a five year research cooperative agreement to a team of researchers from three different universities to address the design and analysis of revolutionary aeropropulsion technologies.
Technical Paper

The Integrated Electric Lifestyle: The Economic and Environmental Benefits of an Efficient Home-Vehicle System

In recent years, the residential and transportation sectors have made significant strides in reducing energy consumption, mainly by focusing efforts on low-hanging fruit in each sector independently. This independent viewpoint has been successful in the past because the user needs met and resources consumed in each sector have been clearly distinct. However, the trend towards vehicle electrification has blurred the boundary between the sectors. With both the home and vehicle now relying upon the same energy source, interactions between the systems can no longer be neglected. For example, when tiered utility pricing schemes are considered, the energy consumption of each system affects the cost of the other. In this paper, the authors present an integrated Home-Vehicle Simulation Model (HVSM), allowing the designer to take a holistic view.
Technical Paper

The Flying Carpet: Aerodynamic High-Altitude Solar Reflector Design Study

Our concept studies indicate that a set of reflectors floated in the upper atmosphere can efficiently reduce radiant forcing into the atmosphere. The cost of reducing the radiant forcing sufficiently to reverse the current rate of Global Warming, is well within reach of global financial resources. This paper summarizes the overall concept and focuses on one of the reflector concepts, the Flying Carpet. The basic element of this reflector array is a rigidized reflector sheet towed behind and above a solar-powered, distributed electric-propelled flying wing. The vehicle rises above 30,480 m (100,000 ft) in the daytime by solar power. At night, the very low wing loading of the sheets enables the system to stay well above the controlled airspace ceiling of 18,288 m (60,000 ft). The concept study results are summarized before going into technical issues in implementation. Flag instability is studied in initial wind tunnel experiments.
Technical Paper

The Direct Transition of Fuel Sprays to theDense-Fluid Mixing Regime in the Contextof Modern Compression Ignition Engines

Fuel supercriticality has recently received significant attention due to the elevated pressures and temperatures that directly-injected (DI) fuel sprays encounter in modern internal combustion (IC) engines. This paper presents a theoretical examination of conventional and alternative DI fuels at conditions relevant to the operation of compression ignition (CI) engines. The focus is to identify the conditions under which the injected liquid fuel can bypass the atomization process and directly transition to a diffusional mixing regime with the chamber gas. Evaluating the microscopic length-scales of the phase boundary associated with the injection of liquid nitrogen into its own vapor, it is found that the conventional threshold based on the interfacial Knudsen number (i.e. Kn = 0.1) does not adequately quantify the direct transition between sub- and supercriticality. Instead, a threshold that is an order of magnitude smaller is more appropriate for this purpose.
Technical Paper

Test Results for a Fuel Cell-Powered Demonstration Aircraft

A fuel cell powered airplane has been designed and constructed at the Georgia Insitute of Technology to develop an understanding of the design and implementation challenges of fuel cell-powered unmanned aerial vehicles (UAVs). A custom 448W net output proton exchange membrane fuel cell powerplant has been constructed and tested. A demonstrator aircraft was designed and built to accommodate this powerplant and the fuel cell powered aircraft has performed seven test flights to date. Test data show that the aircraft performance validates the models used for design and optimization and that the fuel cell aircraft is capable of longer endurance, higher performance test flights.
Journal Article

Technology Selection for Optimal Power Distribution Efficiency in a Turboelectric Propulsion System

Turboelectric propulsion is a technology that can potentially reduce aircraft noise, increase fuel efficiency, and decrease harmful emissions. In a turbo-electric system, the propulsor (fans) is no longer connected to the turbine through a mechanical connection. Instead, a superconducting generator connected to a gas turbine produces electrical power which is delivered to distributed fans. This configuration can potentially decrease fuel burn by 10% [1]. One of the primary challenges in implementing turboelectric electric propulsion is designing the power distribution system to transmit power from the generator to the fans. The power distribution system is required to transmit 40 MW of power from the generator to the electrical loads on the aircraft. A conventional aircraft distribution cannot efficiently or reliably transmit this large amount of power; therefore, new power distribution technologies must be considered.
Technical Paper

Technology Impact Forecasting for a High Speed Civil Transport

This paper outlines a comprehensive, structured, and robust methodology for decision making in the early phases ofaircraft design. The proposed approach is referred to as the Technology Identification, Evaluation, and Selection (TIES) method. The seven-step process provides the decision maker/designer with an ability to easily assess and trade-off the impact of various technologies in the absence of sophisticated, time-consuming mathematical formulations. The method also provides a framework where technically feasible alternatives can be identified with accuracy and speed. This goal is achieved through the use of various probabilistic methods, such as Response Surface Methodology and Monte Carlo Simulations. Furthermore, structured and systematic techniques are utilized to identify possible concepts and evaluation criteria by which comparisons could be made.
Technical Paper

Technology Assessment of a Supersonic Business Jet

This paper presents a quantitative process to track the progress of technology developments within NASA’s Vehicle Systems Program (VSP) as implemented on a Supersonic Business Jet (SBJ). The process, called the Technology Metric Assessment and Tracking (TMAT) process, accounts for the temporal aspects of technology development programs such that technology portfolio assessments, in the form of technological progress towards VSP sector goals, may be tracked and assessed. Progress tracking of internal research and development programs is an essential element to successful strategic endeavors and justification of the pursuit of capital projects [1].
Journal Article

Superconducting Machines and Power Systems for Electric-Drive Aeropropulsion

Societal demands of recent years have increasingly pressured the development of greener technologies in all sectors of the nation's transportation infrastructure, including that of civilian aviation. This study explores the concept of electric-drive aeropropulsion, aided by high-temperature superconducting technology, as an enabler for enhancing the environmental characteristics at the air-vehicle level. Potential improvements in the areas of aircraft noise, emissions, and energy efficiency are discussed in the context of supporting the latest strategic goals of leading governmental organizations.
Technical Paper

Specification of a P3 Parallel Hybrid Electric Vehicle Architecture for the EcoCAR 3 Competition

The Georgia Tech EcoCAR 3 team’s selection of a parallel hybrid electric vehicle (HEV) architecture for the EcoCAR 3 competition is presented in detail, with a focus on the team’s modeling and simulation efforts and how they informed the team’s architecture selection and subsequent component decisions. EcoCAR 3, sponsored by the United States Department of Energy and General Motors, is the latest in a series of Advanced Vehicle Technology Competitions (AVTCs) and features 16 universities from the United States and Canada competing to transform the 2016 Chevrolet Camaro into a hybrid electric American performance vehicle. Team vehicles will be scored on performance, emissions, fuel economy, consumer acceptability, and more over the course of the four-year competition. During the first year, the Georgia Tech team considered numerous component combinations and HEV architectures, including series RWD and AWD, parallel, and power-split.
Technical Paper

Slung Load Divergence Speed Predictions for Vehicle Shapes

Loads slung under aircraft can go into divergent oscillations coupling multiple degrees of freedom. Predicting the highest safe flight speed for a vehicle-load combination is a critical challenge, both for military missions over hostile areas, and for evacuation/rescue operations. The primary difficulty was that of obtaining well-resolved airload maps covering the arbitrary attitudes that a slung load may take. High speed rotorcraft using tilting rotors and co-axial rotors can fly at speeds that imply high dynamic pressure, making aerodynamic loads significant even on very dense loads such as armored vehicles, artillery weapons, and ammunition. The Continuous Rotation method demonstrated in our prior work enables routine prediction of divergence speeds. We build on prior work to explore the prediction of divergence speed for practical configurations such as military vehicles, which often have complex bluff body shapes.
Journal Article

Relationship Between Diesel Fuel Spray Vapor Penetration/Dispersion and Local Fuel Mixture Fraction

The fuel-ambient mixture in vaporized fuel jets produced by liquid sprays is fundamental to the performance and operation of engines. Unfortunately, experimental difficulties limit the direct measurement of local fuel-ambient mixture, inhibiting quantitative assessment of mixing. On the other hand, measurement of global quantities, such as the jet penetration rate, is relatively straightforward. Simplified models to predict local fuel-ambient mixture have also been developed, based on these global parameters. However, experimental data to validate these models over a range of conditions is needed. In the current work, we perform measurements of jet global quantities such as vapor-phase penetration, liquid-phase penetration, spreading angle, and nozzle flow coefficients over a range of conditions in a high-temperature, high-pressure vessel.
Technical Paper

Quiet, Clean, and Efficient, but Heavy - Concerns for Future Fuel Cell Powered Personal Air Vehicles

Unfortunately, the promises of efficient, clean, quiet power that fuel cells offer are balanced by extremely low power densities and great infrastructure-related challenges. Studies by government and industry have investigated their feasibility for primary propulsion in light aircraft. These studies have produced mixed results but have tended to rely on integrating fuel cells into existing airframes, with respectably-performing light sport planes being turned into underpowered show planes with horribly compromised range and payload capabilities. Fuel cells today are in the earliest phases of technological development. As an aircraft propulsion system, they are as advanced as the Wright's reciprocating engine was a hundred years ago.
Technical Paper

Progress in Rotorcraft Icing Computational Tool Development

The formation of ice over lifting surfaces can affect aerodynamic performance. In the case of helicopters, this loss in lift and the increase in sectional drag forces will have a dramatic effect on vehicle performance. The ability to predict ice accumulation and the resulting degradation in rotor performance is essential to determine the limitations of rotorcraft in icing encounters. The consequences of underestimating performance degradation can be serious and so it is important to produce accurate predictions, particularly for severe icing conditions. The simulation of rotorcraft ice accretion is a challenging multidisciplinary problem that until recently has lagged in development over its counterparts in the fixed wing community. But now, several approaches for the robust coupling of a computational fluid dynamics code, a rotorcraft structural dynamics code and an ice accretion code have been demonstrated.
Technical Paper

Probabilistic Analysis of an HSCT Modeled with an Equivalent Laminated Plate Wing

The High Speed Civil Transport (HSCT), a supersonic commercial transport currently under development, presents several challenges to traditional conceptual design. The current historical database used by many commercial transport design processes only include data for subsonic transports and therefore does not apply to innovative new configurations such as the HSCT. Therefore, physics-based, preliminary design tools must be used to model the characteristics of advanced aircraft in conceptual sizing routines. In addition, the evaluation of the aircraft design space often requires the analysis of many configurations in order to assess the impact of design constraints and determine the attainable range of system level metrics, a process which is very time consuming in both modeling and computer run time.