Hybrid wing-body aircraft noise and performance assessment

Abstract

Hybrid wing-body aircraft noise generation and boundary layer ingestion (BLI) performance trends with increased fan face Mach number inlet designs are investigated. The presented topics are in support of the NASA subsonic fixed wing project, which seeks to lower noise and increase performance by improving prediction methods and technologies. The aircraft configurations used for study are the N2A, using conventional podded engines, and the N2B, using an embedded propulsion system. Preliminary FAR Part 36 noise certification assessments are completed using the NASA Aircraft Noise Prediction Program (ANOPP). The limitations of applying current ANOPP noise prediction methods to hybrid wing-body aircraft are investigated. Improvements are made to the landing gear and airfoil self-noise modules, while a diffraction integral method is implemented in a companion thesis to enhance noise shielding estimates. The N2A overall takeoff and landing noise estimate is found to be 5.3 EPNdB higher than the N+2 goal. The dominant noise sources are the fan rearward and jet on takeoff and the main landing gear and elevons on approach. A lower fan pressure ratio and advanced landing gear fairings are recommended to decrease N2A overall noise levels. The available engine noise estimation tools were inadequate to model the N2B distributed propulsion system and rectangular exhaust nozzle; therefore, overall N2B aircraft noise results are presented for reference only. A simplified embedded propulsion system integration study is carried out to explore the N2B fan design space. A 2-D computational domain with contoured slip boundaries around the centerbody is used to replicate the effects of 3-D relief on the airframe and inlet aerodynamics. The domain includes the S-shaped inlet duct and is extended far downstream for a Trefftz plane power balance analysis to determine the propulsive power required for steady level flight. A fan actuator volume is included to couple the airframe external and the engine internal flows. Aircraft power savings, fan efficiency, and boundary layer thickness trends are examined to determine if increasing fan face Mach number improves system performance while mitigating the total pressure distortion risk of boundary layer ingestion. A fan face Mach number near 0.7 is found to increase aircraft power savings 12% relative to the baseline design and to reduce centerbody boundary layer kinetic energy thickness by 4.7%. In addition, power balances at lower fan pressure ratios as fan face Mach number increases suggesting that high-flow low pressure ratio fans are desirable for BLI.