Jeffrey J. Berton

Benefits of Swept-and-Leaned Stators for Fan Noise Reduction

An advanced high bypass ratio fan model was tested in the NASA John H. Glenn Research Center 9 £ 15 Foot Low-Speed Wind Tunnel. The primary focus of this test was to quantify the acoustic benee ts and aerodynamic performance of sweep and lean in stator vanedesign. Three statorsets wereused forthis testseries. Aconventional radial stator set was tested at two rotor ‐stator axial spacings. Additional stator sets incorporating sweep only and sweep and lean were also tested. The hub axial location for the swept-and-leaned and swept-only stators was at the sameaxiallocationastheradialstatoratthesmallerrotor ‐statorspacing (upstreamstatorlocation ),whilethetipof thesemodie edstatorswasatthesameaxiallocation astheradialstatorsetatthedownstream rotor ‐statorspacing. The acoustic data show that swept and leaned stators give signie cant reductions in both rotor ‐stator interaction noise and broadband noise beyond what could be achieved through increased axial spacing of the conventional, radial stator. Application of these test results to a representative two-engine aircraft and e ight path suggest that about a 3 effective perceived noise (EPN)dB fan noise reduction could be achieved through incorporation of these modie ed stators. This reduction would represent a signie cant portion of the6-EPNdB aircraftnoisereduction goal relative to that of 1992 technology levels of the current NASA Advanced Subsonic Technology initiative.

Initial Assessment of Open Rotor Propulsion Applied to an Advanced Single-Aisle Aircraft

Application of high speed, advanced turboprops, or “propfans,” to subsonic transport aircraft received significant attention and research in the 1970s and 1980s when fuel efficiency was the driving focus of aeronautical research. Recent volatility in fuel prices and concern for aviation’s environmental impact have renewed interest in unducted, open rotor propulsion, and revived research by NASA and a number of engine manufacturers. Unfortunately, in the two decades that have passed since open rotor concepts were thoroughly investigated, NASA has lost experience and expertise in this technology area. This paper describes initial efforts to re-establish NASA’s capability to assess aircraft designs with open rotor propulsion. Specifically, methodologies for aircraft-level sizing, performance analysis, and system-level noise analysis are described. Propulsion modeling techniques have been described in a previous paper. Initial results from application of these methods to an advanced single-aisle aircraft using open rotor engines based on historical blade designs are presented. These results indicate open rotor engines have the potential to provide large reductions in fuel consumption and emissions. Initial noise analysis indicates that current noise regulations can be met with old blade designs and modern, noiseoptimized blade designs are expected to result in even lower noise levels. Although an initial capability has been established and initial results obtained, additional development work is necessary to make NASA’s open rotor system analysis capability on par with existing turbofan analysis capabilities.

An Analytical Assessment of NASA's N+1 Subsonic Fixed Wing Project Noise Goal

The Subsonic Fixed Wing Project of NASA’s Fundamental Aeronautics Program has adopted a noise reduction goal for new, subsonic, s ingle-aisle, civil aircraft expected to replace current 737 and A320 airplanes. These so-ca lled “N+1” aircraft ‐ designated in NASA vernacular as such since they will follow the current, in-service, “N” airplanes ‐ are hoped to achieve certification noise goal levels of 32 cumulative EPNdB under current Stage 4 noise regulations. A notional, N+1, single-aisle, twinjet transport with ultrahigh bypass ratio turbofan engines is analyzed in this study us ing NASA software and methods. Several advanced noise-reduction technologies are empirically applied to the propulsion system and airframe. Certification noise levels are predicted and compared with the NASA goal.

Low Noise Cruise Efficient Short Take-Off and Landing Transport Vehicle Study

The saturation of the airspace around current airports combined with increasingly stringent community noise limits represents a serious impediment to growth in world aviation travel. Breakthrough concepts that both increase throughput and reduce noise impacts are required to enable growth in aviation markets. Concepts with a 25 year horizon must facilitate a 4x increase in air travel while simultaneously meeting community noise constraints. Attacking these horizon issues holistically is the concept study of a Cruise Efficient Short Take-Off and Landing (CESTOL) high subsonic transport under the NASAs Revolutionary Systems Concepts for Aeronautics (RSCA) project. The concept is a high-lift capable airframe with a partially embedded distributed propulsion system that takes a synergistic approach in propulsion-airframe-integration (PAI) by fully integrating the airframe and propulsion systems to achieve the benefits of both low-noise short take-off and landing (STOL) operations and efficient high speed cruise. This paper presents a summary of the recent study of a distributed propulsion/airframe configuration that provides low-noise STOL operation to enable 24-hour use of the untapped regional and city center airports to increase the capacity of the overall airspace while still maintaining efficient high subsonic cruise flight capability.

Empennage Noise Shielding Benefits for an Open Rotor Transport

NASA sets aggressive, strategic, civil aircraft performance and environmental goals and develops ambitious technology roadmaps to guide its research efforts. NASA has adopted a phased approach for community noise reduction of civil aircraft. While the goal of the nearterm first phase focuses primarily on source noise reduction, the goal of the second phase relies heavily on presumed architecture changes of future aircraft. The departure from conventional airplane configurations to designs that incorporate some type of propulsion noise shielding is anticipated to provide an additional 10 cumulative EPNdB of noise reduction. One candidate propulsion system for these advanced aircraft is the open rotor engine. In some planned applications, twin open rotor propulsors are located on the aft fuselage, with the vehicle’s empennage shielding some of their acoustic signature from observers on the ground. This study focuses on predicting the noise certification benefits of a notional open rotor aircraft with tail structures shielding a portion of the rotor noise. The measured noise of an open rotor test article – collected with and without an acoustic barrier wall – is the basis of the prediction. The results are used to help validate NASA’s reliance on acoustic shielding to achieve the second phase of its community noise reduction goals. The noise measurements are also compared to a popular empirical diffraction correlation often used at NASA to predict acoustic shielding.

Advanced Single-Aisle Transport Propulsion Design Options Revisited

Future propulsion options for advanced single-aisle transports have been investigated in a number of previous studies by the authors. These studies have examined the system level characteristics of aircraft incorporating ultra-high bypass ratio (UHB) turbofans (direct drive and geared) and open rotor engines. During the course of these prior studies, a number of potential refinements and enhancements to the analysis methodology and assumptions were identified. This paper revisits a previously conducted UHB turbofan fan pressure ratio trade study using updated analysis methodology and assumptions. The changes in propulsion, airframe, and noise modeling are described and discussed. The impacts of these changes are then examined by comparison to the previously reported results. The changes incorporated have decreased the optimum fan pressure ratio for minimum fuel consumption and reduced the engine design trade-offs between minimizing noise and minimizing fuel consumption. Nacelle drag and engine weight are found to be key drivers in determining the optimum fan pressure ratio from a fuel efficiency perspective. The revised noise analysis results in the study aircraft being 2 to 4 EPNdB (cumulative) quieter due to a variety of reasons explained in the paper. With equal core technology assumed, the geared engine architecture is found to be as good as or better than the direct drive architecture for most parameters investigated. However, the engine ultimately selected for a future advanced single-aisle aircraft will depend on factors beyond those considered here.

Turboelectric distributed propulsion benefits on the N3-X vehicle

Purpose – The purpose of this article is to present a summary of recent study results on a turboelectric distributed propulsion vehicle concept named N3-X. Design/methodology/approach – The turboelectric distributed propulsion system uses multiple electric motor-driven propulsors that are distributed on an aircraft. The power to drive these electric propulsors is generated by separately located gas turbine-driven electric generators on the airframe. To estimate the benefits associated with this new propulsion concept, a system analysis was performed on a hybrid-wing-body transport configuration to determine fuel burn (or energy usage), community noise and emissions reductions. Findings – N3-X would be able to reduce energy consumption by 70-72 per cent compared to a reference vehicle, a Boeing 777-200LR, flying the same mission. Predictions for landing and take-off NOX are estimated to be 85 per cent less than the Tier 6-CAEP/6 standard. Two variants of the N3-X vehicle were examined for certification noi...

Multi-Objective Optimization of Turbofan Design Parameters for an Advanced, Single-Aisle Transport

Considerable interest surrounds the design of the next generation of single-aisle commercial transports in the Boeing 737 and Airbus A320 class. Aircraft designers will depend on advanced, next-generation turbofan engines to power these airplanes. The focus of this study is to apply singleand multi-objective optimization algorithms to the conceptual design of ultrahigh bypass (UHB) turbofan engines for this class of aircraft, using NASA’s Subsonic Fixed Wing Project goals as multidisciplinary objectives for optimization. The independent propulsion design parameters investigated are aerodynamic design point fan pressure ratio, overall pressure ratio, fan drive system architecture (i.e., director geardriven), bypass nozzle architecture (i.e., fixedor variable-geometry), and the highand lowpressure compressor work split. NASA Project goal metrics – fuel burn, noise, and emissions – are among the parameters treated as dependent objective functions. These optimized solutions provide insight to the UHB engine design process and provide independent information to NASA program management to help guide its technology development efforts. This assessment leverages results from earlier NASA system concept studies conducted in 2008 and 2009, in which UHB turbofans were examined for a notional, nextgeneration, single-aisle transport. The purpose of these NASA UHB engine concept studies is to determine if the fuel consumption and noise benefits of engines having lower fan pressure ratios (and correspondingly higher bypass ratios) translate into overall aircraft system-level benefits for a 737 class vehicle.

Open-Source Conceptual Sizing Models for the Hyperloop Passenger Pod

Hyperloop is a new mode of transportation proposed as an alternative to Californias high speed rail project, with the intended benefits of higher performance at lower overall costs. It consists of a passenger pod traveling through a tube under a light vacuum and suspended on air bearings. The pod travels up to transonic speeds resulting in a 35 minute travel time between the intended route from Los Angeles and San Francisco. Of the two variants outlined, the smaller system includes a 1.1 meter tall passenger capsule traveling through a 2.2 meter tube at 700 miles per hour. The passenger pod features water-based heat exchangers as well as an on-board compression system that reduces the aerodynamic drag as it moves through the tube. Although the original proposal looks very promising, it assumes that tube and pod dimensions are independently sizable without fully acknowledging the constraints of the compressor system on the pod geometry. This work focuses on the aerodynamic and thermodynamic interactions between the two largest systems; the tube and the pod. Using open-source toolsets, a new sizing method is developed based on one-dimensional thermodynamic relationships that accounts for the strong interactions between these sub-systems. These additional considerations require a tube nearly twice the size originally considered and limit the maximum pod travel speed to about 620 miles per hour. Although the results indicate that Hyperloop will need to be larger and slightly slower than originally intended, the estimated travel time only increases by approximately five minutes, so the overall performance is not dramatically affected. In addition, the proposed on-board heat exchanger is not an ideal solution to achieve reasonable equilibrium air temperatures within the tube. Removal of this subsystem represents a potential reduction in weight, energy requirements and complexity of the pod. In light of these finding, the core concept still remains a compelling possibility, although additional engineering and economic analyses are markedly necessary before a more complete design can be developed.

A Noise and Emissions Assessment of the N3-X Transport

Analytical predictions of certification noise and exhaust emissions for NASA’s N3-X – a notional, hybrid wingbody airplane – are presented in this paper. The N3-X is a 300passenger concept transport propelled by an array of fans distributed spanwise near the trailing edge of the wingbody. These fans are driven by electric motors deriving power from twin generators driven by turboshaft engines. Turboelectric distributed hybrid propulsion has the potential to dramatically increase the propulsive efficiency of aircraft. The noise and exhaust emission estimates presented here are generated using NASA’s conceptual design systems analysis tools with several key modifications to accommodate this unconventional architecture. These tools predict certification noise and the emissions of oxides of nitrogen by leveraging data generated from a recent analysis of the N3-X propulsion system.