Hybrid Wing Body Aircraft System Noise Assessment with Propulsion Airframe Aeroacoustic Experiments

Abstract

A system noise assessment of a hybrid wing body configuration was performed using NASA's best available aircraft models, engine model, and system noise assessment method. A propulsion airframe aeroacoustic effects experimental database for key noise sources and interaction effects was used to provide data directly in the noise assessment where prediction methods are inadequate. NASA engine and aircraft system models were created to define the hybrid wing body aircraft concept as a twin engine aircraft with a 7500 nautical mile mission. The engines were modeled as existing technology high bypass ratio turbofans. The baseline hybrid wing body aircraft was assessed at 22 dB cumulative below the FAA Stage 4 certification level. To determine the potential for noise reduction with relatively near term technologies, seven other configurations were assessed beginning with moving the engines two fan nozzle diameters upstream of the trailing edge and then adding technologies for reduction of the highest noise sources. Aft radiated noise was expected to be the most challenging to reduce and, therefore, the experimental database focused on jet nozzle and pylon configurations that could reduce jet noise through a combination of source reduction and shielding effectiveness. The best configuration for reduction of jet noise used state-ofthe-art technology chevrons with a pylon above the engine in the crown position. This configuration resulted in jet source noise reduction, favorable azimuthal directivity, and noise source relocation upstream where it is more effectively shielded by the limited airframe surface, and additional fan noise attenuation from acoustic liner on the crown pylon internal surfaces. Vertical and elevon surfaces were also assessed to add shielding area. The elevon deflection above the trailing edge showed some small additional noise reduction whereas vertical surfaces resulted in a slight noise increase. With the effects of the configurations from the database included, the best available noise reduction was 40 dB cumulative. Projected effects from additional technologies were assessed for an advanced noise reduction configuration including landing gear fairings and advanced pylon and chevron nozzles.

High Bypass Ratio Jet Noise Reduction and Installation Effects Including Shielding Effectiveness

“…Finally, the nozzle configuration with a more strongly immersed chevron and the conventional pylon oriented opposite to the ground observers (not used to attach engine to airframe) produced the largest overall reduction in jet noise including source and shielding effects combined. This nozzle configuration was selected as best for the bypass ratio 7 application to the GE90-like engine and HWB system noise assessment of Thomas, Burley and Olson 13 . In addition, the vertical and elevon airframe control surfaces had small effects and were also documented and assessed in the system noise results 12,13 .…”

“…This nozzle configuration was selected as best for the bypass ratio 7 application to the GE90-like engine and HWB system noise assessment of Thomas, Burley and Olson 13 . In addition, the vertical and elevon airframe control surfaces had small effects and were also documented and assessed in the system noise results 12,13 .…”

“…This configuration, now applied to the BPR 10 cycle, is the same design type of the best nozzle configuration selected in the prior work [12][13] for the BPR 7 application. The T-fan chevrons are designed similarly to the chevron termed Chev2 of Czech, Thomas, and Elkoby 12 .…”

“…A high fidelity wind tunnel model has been built and tested at NASA Langley's 14 by 22 Foot Subsonic Wind Tunnel for low speed aerodynamic performance by Gatlin, Vicroy and Carter 14 and is to be tested for its aeroacoustic characteristics starting late in 2012 in the aeroacoustic configuration of the same wind tunnel. While incorporating some of the same key features for noise reduction as the study of Thomas, Burley, and Olson 13 , such as the placement of the engines at least two engine diameters upstream of the trailing edge, this concept also specified an engine of a bypass ratio 10 compared to the bypass ratio 7 of the GE90-like engine from the earlier study 13 .…”

The Effects of Surfaces on the Aerodynamics and Acoustics of Jet Flows

“…This effect is described by Thomas et al 7 and Czech et al 8 Several techniques have been developed to predict the scattered noise from the engine. Some of these techniques include the Boundary Element Method, 2 the Equivalent Source Method used in NASA's Fast Scattering Code, 9 and the ray tracing method.…”