System Noise Assessment and the Potential for Low Noise Hybrid Wing Body Aircraft with Open Rotor Propulsion

Abstract

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.

Novel Propeller Map Scaling Method

“…The developed scaling technique is tested by scaling a baseline propeller map in order to obtain a map of a different propeller design. In a period when there is a renewed interest in turboprop aircraft [11,12] and open-rotor engines are always under investigation [4,[13][14][15][16][17][18], the scaling method proposed in this paper can be a valuable tool both for industrial and academic preliminary design studies.…”

“…After the calculation of the viscous losses and of the total propeller efficiency, one can use Eqs. (15)(16)(17)(18)(19)(20)(21) in order to calculate the ideal power coefficient, and subsequently use Eqs. (5)(6)(7)(8)(9)(10)(11)(12)(13)(14) once more to calculate the final ideal efficiency.…”

“…8) The process returns back to step 3, but this time, Eqs. (15)(16)(17)(18)(19)(20)(21) can be used to calculate the ideal power coefficient C scaled Pi using the η scaled prop calculated in step 5. One only iteration should normally suffice.…”

Compact Assumption Applied to Monopole Term of Farassat’s Formulations

“…Community noise has been an ongoing problem for aircraft and is projected to be a major concern in the future due to increased air traffic. 1 Both conventional and unconventional aircraft designs continue to be evaluated, 2,3 in which assessments are performed using aircraft noise prediction and measured data if available. Aircraft designs increasingly include acoustics in the design process, and therefore require many estimations of the noise without the fine detail that is required to do an in-depth acoustic assessment.…”

A Conventional Liner Acoustic/Drag Interaction Benchmark Database

“…1) are required to meet community noise goals. 4 For these applications, liner aerodynamic performance could be crucial to enabling such advanced aircraft configurations.…”