The requirements, constraints, and design of NASA's next generation Aircraft NOise Prediction Program (ANOPP2) are introduced. Similar to its predecessor (ANOPP), ANOPP2 provides the U.S. Government with an independent aircraft system noise prediction capability that can be used as a stand-alone program or within larger trade studies that include performance, emissions, and fuel burn. The ANOPP2 framework is designed to facilitate the combination of acoustic approaches of varying fidelity for the analysis of noise from conventional and unconventional aircraft. ANOPP2 integrates noise prediction and propagation methods, including those found in ANOPP, into a unified system that is compatible for use within general aircraft analysis software. The design of the system is described in terms of its functionality and capability to perform predictions accounting for distributed sources, installation effects, and propagation through a non-uniform atmosphere including refraction and the influence of terrain. The philosophy of mixed fidelity noise prediction through the use of nested Ffowcs Williams and Hawkings surfaces is presented and specific issues associated with its implementation are identified. Demonstrations for a conventional twin-aisle and an unconventional hybrid wing body aircraft configuration are presented to show the feasibility and capabilities of the system. Isolated model-scale jet noise predictions are also presented using high-fidelity and reduced order models, further demonstrating ANOPP2's ability to provide predictions for model-scale test configurations.

In this paper, a near-real time rotorcraft flight dynamics-acoustics prediction system is presented. Limited internal consistency checks and comparison with previous maneuver noise predictions, based on CAMRAD 2 airloads and motions, are presented to partially validate the system. A complex 80-second maneuver was used to demonstrate the capability of the coupled GENHEL-PSU-WOPWOP system. This realistic maneuver includes a climb, coordinated turn, and level flight conditions. Prediction of overall sound pressure level was performed over a region 2000 meters by 1600 meters with 8181 individual measurement locations. The noise predictions show changes in noise radiation strength and directivity due to maneuver transients, aircraft attitude changes, and the aircraft flight. A comparison of the total noise with the thickness and loading noise components helps explain the noise directivity. The computations for a single observer were very fast-although not real-time. Real-time loading noise prediction is demonstrated and the feasibility of real-time noise prediction of the total noise signal is evaluated.

An aircraft system noise assessment was conducted for a hybrid wing body freighter aircraft concept configured with three open rotor engines. The primary objective of the study was to determine the aircraft system level noise given the significant impact of installation effects including shielding the open rotor noise by the airframe. The aircraft was designed to carry a payload of 100,000 lbs on a 6,500 nautical mile mission. An experimental database was used to establish the propulsion airframe aeroacoustic installation effects including those from shielding by the airframe planform, interactions with the control surfaces, and additional noise reduction technologies. A second objective of the study applied the impacts of projected low noise airframe technology and a projection of advanced low noise rotors appropriate for the NASA N+2 2025 timeframe. With the projection of low noise rotors and installation effects, the aircraft system level was 26.0 EPNLdB below Stage 4 level with the engine installed at 1.0 rotor diameters upstream of the trailing edge. Moving the engine to 1.5 rotor diameters brought the system level noise to 30.8 EPNLdB below Stage 4. At these locations on the airframe, the integrated level of installation effects including shielding can be as much as 20 EPNLdB cumulative in addition to lower engine source noise from advanced low noise rotors. And finally, an additional set of technology effects were identified and the potential impact at the system level was estimated for noise only without assessing the impact on aircraft performance. If these additional effects were to be included it is estimated that the potential aircraft system noise could reach as low as 38.0 EPNLdB cumulative below Stage 4.

An aircraft system noise assessment was performed for the hybrid wing body aircraft concept, known as the N2A-EXTE. This assessment is a result of an effort by NASA to explore a realistic HWB design that has the potential to substantially reduce noise and fuel burn. Under contract to NASA, Boeing designed the aircraft using practical aircraft design principles with incorporation of noise technologies projected to be available in the 2020 timeframe. NASA tested a 5.8% scale-model of the design in the NASA Langley 14-by 22-Foot Subsonic Tunnel to provide source noise directivity and installation effects for aircraft engine and airframe configurations. Analysis permitted direct scaling of the model-scale jet, airframe, and engine shielding effect measurements to full-scale. Use of these in combination with ANOPP predictions enabled computations of the cumulative (CUM) noise margins relative to FAA Stage 4 limits. The CUM margins were computed for a baseline N2A-EXTE configuration and for configurations with added noise reduction strategies. The strategies include reduced approach speed, over-the-rotor liner and soft-vane fan technologies, vertical tail placement and orientation, and modified landing gear designs with fairings. Combining the inherent HWB engine shielding by the airframe with added noise technologies, the cumulative noise was assessed at 38.7 dB below FAA Stage 4 certification level, just 3.3 dB short of the NASA N+2 goal of 42 dB. This new result shows that the NASA N+2 goal is approachable and that significant reduction in overall aircraft noise is possible through configurations with noise reduction technologies and operational changes. Nomenclature ANOPP = NASA's aircraft noise prediction program 1 ANOPP2 = NASA's aircraft noise prediction program2, a multi-fidelity framework AOA = angle of attack, degrees AP = approach flight condition BENS = broadband engine noise simulators BPR = engine bypass ratio CB = cutback flight conditionThis material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. AIAA Aviation 2 CJES = compact jet engine simulators CUM = cumulative noise (summation of takeoff, cutback and approach EPNL), EPNdB D = fan nozzle exit diameter, ft. dB = decibel EPNL = effective perceived noise level, dB, also referred to as EPNdB FLOPS = flight optimization system 2 f = frequency HWB = hybrid wing body LE = leading edge L/D = lift/drag M = Mach number PNL = perceived noise level, dB PNLT = tone-corrected perceived noise level, dB R = distance from source to observer SF = model-scale/full-scale = 0.058 SFC = specific fuel consumption SL = sideline (full-throttle flight condition) certification point SPL = sound pressure level X = axial coordinate, ft. Greek φ = azimuthal directivity angle, degrees θ = polar directivity angle, degrees Subscript fs = full-scale ms = model-scale nb = narrowband

I. AbstractThis paper describes the initial development of a method for the prediction of the noise radiated by aircraft landing gear. Called the Landing Gear Model and Acoustic Prediction (LGMAP), it will eventually include all the geometric complexity of a realistic landing gear. This will be achieved by dividing the gear into a number of elements or objects. The noise from each of these elements is described by a simple acoustic model. Each object has three attributes; its geometry and location, and an upstream and downstream environment. This enables the flow or noise from one element to interact with any other. The method is designed to allow improved element acoustic models to be introduced as they become available. This paper contains some initial examples for two objects; a cylinder element and a wheel model. The landing gear is divided into assemblies made up of these elements. The radiated noise is calculated in the timedomain using a source-time-dominant solution to the Ffowcs Williams-Hawkings equation. This initial, rather crude, model is calibrated by comparison with experiment and existing noise prediction methods. The purpose of this paper is primarily to introduce the modeling philosophy rather than make extensive predictions. Though more than one example is given. The model is still in its early development stages and many important acoustic mechanisms are not included. Some of the future plans and necessary extensions to the model are discussed.