The Quiet Technology Demonstrator Program: Flight Validation of Airplane Noise-Reduction Concepts

With continued growth in air travel, sensitivity to community noise intensifies and materializes in the form of increased monitoring, regulations, and restrictions. Accordingly, realization of quieter aircraft is imperative, albeit only achievable with reduction of both engine and airframe components of total aircraft noise. Model-scale airframe noise testing has aided in this pursuit; however, the results are somewhat limited due to lack of fidelity of model hardware, particularly in simulating full-scale landing gear. Moreover, simulation of true in-flight conditions is non-trivial if not infeasible. This paper reports on an investigation of full-scale landing gear noise measured as part of the 2005 Quiet Technology Demonstrator 2 (QTD2) flight test program. Conventional Boeing 777-300ER main landing gear were tested, along with two noise reduction concepts, namely a toboggan fairing and gear alignment with the local flow, both of which were down-selected from various other noise reduction devices evaluated in model-scale testing at Virginia Tech. The full-scale toboggan fairings were designed by Goodrich Aerostructures as add-on devices allowing for complete retraction of the main gear. The baseline-conventional gear, faired gear, and aligned gear were all evaluated with the high-lift system in the retracted position and deployed at various flap settings, all at engine idle power setting. Measurements were taken with flyover community noise microphones and a large aperture acoustic phased array, yielding far-field spectra, and localized sources (beamform maps). The results were utilized to evaluate qualitatively and quantitatively the merit of each noise reduction concept. Complete similarity between model-scale and full-scale noise reduction levels was not found and requires further investigation. Far-field spectra exhibited no noise reduction for both concepts across all angles and frequencies. Phased array beamform maps show inconclusive evidence of noise reduction at selective frequencies (1500 to 3000 Hz) but are otherwise in general agreement with the far-field spectra results (within measurement uncertainty).

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Airframe Noise Results from the QTD II Flight Test Program

The New York Times announced America's entry into the 'long awaited' Jet Age when a Pan American (Pan Am) World Airways Boeing 707 airliner left New York for Paris on October 26, 1958. Powered by four turbojet engines, the 707 offered speed, more nonstop flights, and a smoother and quieter travel experience compared to newly antiquated propeller airliners. With the Champs-Elysees only 6 hours away, humankind had entered into a new and exciting age in which the shrinking of the world for good was no longer a daydream. Fifty years later, the New York Times declared the second coming of a 'cleaner, leaner' Jet Age. Decades-old concerns over fuel efficiency, noise, and emissions shaped this new age as the aviation industry had the world poised for 'a revolution in jet engines'. Refined turbofans incorporating the latest innovations would ensure that aviation would continue to enable a worldwide transportation network. At the root of many of the advances over the preceding 50 years was the National Aeronautics and Space Administration (NASA). On October 1, 1958, just a few weeks before the flight of that Pan Am 707, NASA came into existence. Tasked with establishing a national space program as part of a Cold War competition between the United States and the Soviet Union, NASA is often remembered in popular memory first for putting the first human beings on the Moon in July 1969, followed by running the successful 30-year Space Shuttle Program and by landing the Rover Curiosity on Mars in August 2012. What many people do not recognize is the crucial role the first 'A' in NASA played in the development of aircraft since the Agency's inception. Innovations shaping the aerodynamic design, efficient operation, and overall safety of aircraft made NASA a vital element of the American aviation industry even though they remained unknown to the public. This is the story of one facet of NASA's many contributions to commercial, military, and general aviation: the development of aircraft propulsion technology, which provides the power for flight.

https://ntrs.nasa.gov/api/citations/20180003207/downloads/20180003207.pdf

The Power for Flight: NASA’s Contributions to Aircraft Propulsion

During the Quiet Technology Demonstrator 2 program, a GE90-115B engine was tested statically which provided the opportunity to demonstrate several advanced phased array systems for measuring inlet noise. In order of increasing complexity, these included a 10 element microphone arc array located in the acoustic near-field, a 100 element Kulite array mounted on the aeroacoustic bellmouth, and a 275 element Kulite array mounted on the turbulence control structure (TCS). This paper discusses the design objectives, implementation, and sample results from these arrays. The source localization capability of the relatively simple microphone arc array was demonstrated. The inlet noise was also decomposed into its modal content by both the bellmouth array and TCS array for a subsonic and a transonic fan tip relative Mach number. These phased array systems were successfully deployed to demonstrate the capabilities of the advanced measurements and provide useful insights into inlet radiated fan and compressor noise.

Phased Array Measurements of Full-Scale Engine Inlet Noise

The focus of this thesis is the measurement of broadband fan noise, which due to reductions in tonal and jet noise, is now the dominant source at approach, and a major contributor at takeoff. This thesis proposes three new in-duct measurement techniques for the characterisation and measurement of broadband fan noise. A complete characterisation of broadband noise involves determining the sources of sound, their location,and the sound field they generate.The first new in-duct measurement technique uses inverse methods to determine the noise source strengths on a ducted fan. The novel aspect of this technique is that it allows source strengths to be determined both in the rotating (or rotor-bound) reference frame and stationary (stator-bound) reference frame.The second technique is the development of an in-duct, rotating focus beamformer that allows beam forming in both rotating and stationary reference frames using an in-duct microphone array. The ability of the beam former to determine the strengths of the rotor-based and stator-based sources is demonstrated using numerical simulations, with particular emphasis on the determination of the relative contributions of the rotor and the stator to overall broadband noise. The third measurement technique is designed to allow radiated directivity patterns to be predicted from in-duct measurements. This technique allows the prediction of radiated directivity from hollow no-flow ducts, fan inlets and annular exhaust ducts from in-duct measurements. The technique is also validated using experimental data acquired from a no-flow duct rig. Finally, an in-situ phase calibration method for in-duct axial arrays is proposed. This technique allows the rapid calibration of microphone arrays used in the three measurement techniques presented in the thesis. The technique is validated using experimental data.

In-duct measurement techniques for the characterisation of broadband aeroengine noise

*† ‡ § ** †† This paper describes a successful programme undertaken by Boeing and Rolls-Royce to demonstrate nacelle based noise reduction technologies including advanced nozzle and enhanced inlet nacelle designs. The programme, completed between 2001 and 2002, demonstrated jet noise reductions in flight, of up to 4dB, for hot and cold nozzle serrations, confirming pre-test expectations based on model test work. Forward propagating fan noise reductions of up to 13dB were achieved at blade passing frequency (BPF) with a new Boeing developed acoustically enhanced inlet (Amax). Acoustic pressure transducer arrays located forward and downstream of the fan, during static engine testing, helped identify that the Amax inlet fan noise reductions were largely attributable to minimising scattering of acoustic modes and the axial extent of the new liner. Results from this programme highlight the benefit of engine and airframe manufacturers working together to reduce overall aircraft noise levels, and have demonstrated the readiness of the tested technologies for production incorporation.

The Joint Rolls-Royce/Boeing Quiet Technology Demonstrator Programme

During the early stage of an aircraft take-off grou nd manoeuvre natural cross winds can initiate intermittent flow separation within the en gine intake. The risk of separation is greatest when the engine is operating at the highes t power and the aircraft speed is low. This paper presents a new approach for the prediction of unsteady intake flow performance during the aircraft take-off phase in natural cross winds including the effects of rolling takeoff (a take-off in which the engine power increase and the aircraft ground speed increase are simultaneous). The method described is based on a statistical model of the performance of a forward moving engine intake operating within unsteady natural wind, utilising a wind engineering approach. The model provides a description of the perceived wind conditions as a function of aircraft forward speed and allows the intake flow characteristics at any point in the take-off phase to be calculated. The results fo r two subsonic engine inlets demonstrate a relationship between intake aerodynamic performance, engine power increase with aircraft forward speed and required runway length. Over the engine lifetime, rolling take-off is shown to significantly reduce the likelihood of int ake flow separation at high engine power.

Intake performance during rolling take-off in natural crosswind

In order to meet the ACARE environmental goals further noise reduction from aircraft operation is required relative to that achieved to date. To support this aim the European Commission Seventh Framework Programme promotes the “Optimisation for low Environmental Noise impact AIRcraft (OPENAIR)” programme. Within the OPENAIR programme Rolls-Royce leads the Integrated Propulsion System Design sub platform containing a task to produce multi disciplinary optimized Fan System outlet guide vane (OGV) designs. As a partner in this task, DLR have undertaken an aerodynamic optimized design for a novel OGV concept as the first part within this task.As a starting point, Rolls-Royce specified a high bypass ratio turbo fan engine style and a novel OGV number and space envelope within the engine. Within the EU FP6 VITAL programme a lower number of OGVs compared to current practice was investigated [1] and Rolls-Royce had previously undertaken rig tests of a range of fan / OGV blade ratios and showed potential noise penalties but also benefits, particularly for the higher tone harmonics and broadband noise for very low numbers of OGVs [2]. The advent of multidisciplinary optimization techniques for noise, aerodynamics and mechanical constraints led Rolls-Royce to specify a very low number of OGVs to investigate the benefits and the mitigation of the penalties using these optimization techniques. The multidisciplinary design optimization was planned to be undertaken in two parts. The aim of the first part, to be reported in this paper, was to achieve a good aerodynamic design for the novel OGV concept. Controlling the aerodynamic secondary losses was expected to be a challenge for the novel concept. The second part of the optimisation will also include noise.As part of the initial design optimization study within OPENAIR, DLR present a multi objective aerodynamic design optimization for the novel very low OGV number and space envelope specified. The blade number of the OGV was reduced from 42 to 14. The first design phase covered the two dimensional airfoil section design for the reduced blade count OGV. In order to achieve an enhanced aerodynamic performance with a reduced blade number an automated process chain was used to couple the DLR in house optimiser AutoOpti [3, 4] with the two dimensional flow solver MISES [5]. Three operating points were considered in the aerodynamic design covering a wide range of the compressor operating map.It has been found that the design of a low blade count OGV is feasible by means of good aerodynamic performance. Additionally the aerodynamic losses could be reduced in all operating points further and small flow separation areas on the suction surface closed to the hub and tip endwalls implied a further improvement potential. Therefore, the second design phase was focused on the three dimensional endwall optimisation including a variable flow duct and fillet geometry. An automated process chain was established for this purpose. As a result the flow separation was prevented in all operating points. In the last step of the DLR work a high fidelity URANS simulation of the configuration with the newly designed OGV was conducted to assess its aero-acoustical behavior at this stage of the aerodynamically optimized OGV design and the emitted sound power level downstream the OGV for the optimised low blade number configuration is presented in this work.Copyright © 2012 by Rolls-Royce plc

Nicholas D. Humphreys

Papers

The Joint Rolls-Royce/Boeing Quiet Technology Demonstrator Programme

Intake performance during rolling take-off in natural crosswind

Optimised Aerodynamic Design of an OGV With Reduced Blade Count for Low Noise Aircraft Engines