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FUNDAMENTAL AERONAUTICS - RESEARCH OPPORTUNITIES - SUBSONIC FIXED WING

Conceptual art of subsonic fixed wing aircraft

A major focus of the Subsonic Fixed Wing Project is development of improved prediction methods and technologies for lower noise, lower emissions, and higher performance for subsonic aircraft. Increased performance requires expansion of the allowable flight envelope, increased structural reliability with reduced structural weight, and increased energy efficiency and operability for advanced airframe and engine systems and subsystems. While there are no specific system-level goals for noise, emissions, and performance, technologies will be evaluated using trade studies for typical engines and aircraft. The 10-year strategy includes provisions for novel test methods and validated prediction tools that can be used to improve system tradeoffs for advanced concepts capable of meeting longer-term noise, emissions, and performance targets. It is expected that foundational research performed throughout the project will lead to:

  • Improvements in MDAO multidisciplinary design, analysis, and optimization tools
  • New experimental methods that provide fundamental properties and establish validation data
  • Noise prediction and reduction technologies for airframe and propulsion systems
  • Emissions reduction technologies (with emphasis on NOx reduction), alternative fuels, and particulate measurement methods
  • Improved vehicle performance through design and development of lightweight, multifunctional and durable structural components, high-lift aerodynamics, and higher bypass ratio engines with efficient power plants

Subsonic Fixed Wing Project Key Research Areas:

Fundamental Design and Optimization Capabilities

New Experimental Methods/Capabilities

Noise Reduction

Emissions Reduction

Improved Performance

 

Fundamental Design and Optimization Capabilities

System-level optimization, assessment, and technology integration is an approach to solve the aeronautics challenges for a broad range of subsonic air vehicles. The challenge of enhancing system-level design and analysis capabilities in order to perform accurate tradeoffs between performance, noise, and emissions must incorporate more physics-based methodologies. Current interdisciplinary design and analysis involve a multitude of tools and methods not necessarily developed to work together, hindering their application to complete system design and analysis. These tools have inherent limitations that preclude the modeling of unconventional systems to the same fidelity as conventional configurations. The goal of the project is development of fast and effective physics-based, multidisciplinary analysis and design tools with optimization capabilities that quantify levels of uncertainty, enabling virtual expeditions through the design space.

Substantial performance improvements can be realized by developing closely integrated design procedures coupled with high-fidelity analyses during detailed design. Design procedures must enable rapid determination of sensitivities (gradients) of a design objective with respect to all design variables and constraints; take into account the need to choose search directions through design space without violating constraints; and make appropriate changes to the vehicle shape and size (ideally both external Outer Mold Line [OML] shape and internal structural element size). Research interests include integrated design optimization tools that exercise combinations of design variables synergistically to produce superior performance compared to the results of sequential, single-discipline optimization or repeated cut-and-try analysis.

Realizing this topic goal will enable a more robust vehicle design and analysis capability through a shift from empirically based, non-integrated, low-fidelity deterministic methods to more physics-based, integrated, variable-fidelity probabilistic methods.

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New Experimental Methods/Capabilities

Advanced measurement techniques and experimental methods are required that would directly support research leading to reduced noise, reduced emissions, and increased vehicle performance. Innovative new approaches to current measurement techniques used in the testing and simulation environment are required to enhance critical facilities and capabilities used for validation of advanced concepts. Areas of interest include structures and materials characterization, intelligent engine design, enhanced aerodynamic testing, and improved flight research techniques.

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Noise Reduction

Innovative ideas, methods, and technologies are needed for the design and development of low-noise aircraft. Improvements in physics-based noise prediction methods, high-resolution noise and flow measurement techniques, robust noise control and mitigation strategies, and novel low-noise aircraft concepts are necessary to enable anticipated growth in air traffic worldwide while complying with increasingly restrictive controls on community noise levels. As part of a multi-pronged strategy to tackle this challenge, novel ideas are needed in advanced prediction and measurement techniques, innovative noise-reduction methods, low-noise propulsion/airframe integration concepts, unconventional low-noise aircraft configurations, and low-noise operations/noise mitigation procedures.

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Emissions Reduction

Innovative ideas, methods, and technologies are needed for the design and development of low-emissions combustors. Fundamental combustion research coupled with associated physics-based model development of combustion processes needs to be performed to provide the foundation for technology development critical for emissions reduction. Combustion typically involves multiphase, multicomponent-fuel, turbulent, unsteady, and 3-D reacting flows, where much of the physics of the processes is not completely understood. Computational fluid dynamics (CFD) codes are needed for reactive flows that have comparable accuracy to current non-reacting flow codes. Practical combustion concepts are needed for very rapid mixing of the fuel and air with a minimum pressure loss to achieve complete combustion in the smallest volume. Alternative fuel technologies (e.g., Fischer-Tropsch, bio-fuels) need to be developed for aircraft applications to reduce emissions, improve performance, and decrease the nation's dependence on oil. Reliable particulate measurement methods are needed for combustor and collaborative engine tests to be sponsored by NASA and industry partners.

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Improved Performance

The challenge of flight has its foundations in basic disciplines such as structural performance and control and the understanding, prediction, and control of fluid flow around complex geometries. Reliable structural, aerodynamic (vehicle system), and aerothermodynamic (engine) predictions are needed throughout the flight envelope for multiple missions. This project will develop innovative physics-based models and novel concepts with an emphasis on low weight/higher operational limit structural concepts for airframe and propulsion systems, and aerodynamic concepts with an emphasis on flow control methods enabling high lift and low drag.

Accurate analysis tools are required to ensure reliable predictions of complex structural response for innovative designs and novel materials under a complete range of flight conditions. Additionally, predictions are needed for flow separation onset/progression on smooth, curved surfaces and the control of separation, especially at transonic speeds. Advanced flow control technologies are needed to alleviate these problems. Enabling technologies for Ultra High Bypass (UHB) engines and high-power density cores are needed, including accurate simulations for highly loaded turbomachinery and innovative ideas incorporating flow control for increasing compression system work factors while maintaining or increasing efficiency and operability. Improvements in turbine cooling effectiveness, secondary flow, and component matching are also needed for high-pressure-ratio engines. Finally, adaptive, multifunctional materials and structures concepts can enable new aircraft configurations and offer improved performance to more conventional aircraft configurations through significant weight reductions, increased lifetime and operability, increased operating temperatures, reduced repair costs, self-healing, and imbedded structural state monitoring.

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