Open Rotor Designs for Low Noise and High Efficiency

Abstract

Building upon the successes of the UDF® program in the 1980’s, open rotor designs for high flight speed efficiency and low community noise have been developed at GE in collaboration with NASA and the FAA. Targeting a narrow body aircraft with 0.78 cruise Mach number, the cost-share program leveraged computational fluid dynamics (CFD), computational aero-acoustics (CAA), and rig scale testing to generate designs that achieved significant noise reductions well beyond what was attained in the 1980’s while substantially retaining cruise performance. This paper presents overall propeller net efficiency and acoustic assessments of GE’s modern open rotor designs based on measured rig data and the progression of the technology from the 1980’s through the present. Also discussed are the effects of aft rotor clipping, inter-rotor spacing, and disk loading. This paper shows how the two-phase design and scale model wind tunnel test program allowed for test results of the first design phase to feed back into the second design phase, resulting in 2–3% improvement in overall propeller net efficiency than the best efficiency design of the 1980’s while nominally achieving 15–17 EPNdB noise margin to Chapter 4 (when projected to full scale for a prescribed aircraft trajectory and installation). Accounting for trades and near term advancements, such a propulsion system is projected to meet the goal of 26% fuel burn reduction relative to CFM56-7B powered narrow body aircraft.

Prediction of the Aero-Acoustic Performance of Open Rotors

“…Current open rotor efforts make extensive use of modern three-dimensional computational fluid dynamics (CFD) and computational aeroacoustics (CAA) tools to produce designs that are both high-efficiency and low-noise (3)(4)(5). Additionally, computational methods have been used to further investigate the mechanisms of open rotor noise generation in order to develop rules for low-noise blade designs.…”

Progress in open rotor propulsors: The FAA/GE/NASA open rotor test campaign

“…The GE analysis is described in Ref. 7. Unlike the NASA assessment, GE's fuel burn analysis was based on an internal model of a Boeing 737-800W 162 seat aircraft for an 800nm mission at Mach 0•78 cruise.…”

Auralization of Flyover Noise from Open-Rotor Engines Using Model-Scale Test Data

“…The current effort takes advantage of contemporary computational fluid dynamics and computational aeroacoustic tools to optimize blade designs for both aeroperformance and reduced noise emissions. NASA, Federal Aviation Administration (FAA), and GE have collaborated to design, build, and test new generations of low-noise high-efficiency open rotors [5,6]. Aerodynamic performance and acoustic measurements from this test series have been used to perform aircraft-system-level analyses for fuel burn and community noise.…”

“…Aerodynamic performance and acoustic measurements from this test series have been used to perform aircraft-system-level analyses for fuel burn and community noise. The new generation of open-rotor designs is predicted to have an effective perceived-noise level (EPNL) of 15-17 EPNdB cumulative margin relative to Chapter 4 noise regulations [7,8] for the NASA modern open-rotor single-aisle aircraft application [5,6,9]. However, community-noise levels based on integrated sound exposure do not adequately capture the remarkable acoustic improvements of the latest generation designs for a layperson.…”

“…Because the source-noise-prediction models for open-rotor engines are a topic of current research [13], the present effort uses the aforementioned wind-tunnel-test data [5,6] as input for the noise synthesis of both the second-generation (Gen-2) concepts, as well as the historical reference blade design. The latter blade was designed for optimal aeroperformance without considering acoustic performance.…”