Trevor Howard Wood

Open Rotor Designs for Low Noise and High Efficiency

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.Copyright

Stability of high Reynolds number flow past a circular aperture

An analysis is made of the canonical problem of flow at very high Reynolds number past a circular aperture in a thin rigid wall. The motion is incompressible, and the shear layer over the aperture is treated as a vortex sheet separating two parallel flows of unequal mean velocities. Viscosity is neglected except for its role in shedding vorticity from the upstream semicircular edge of the aperture. Nominally steady flow is unstable, and often accompanied by large amplitude self–sustaining oscillations at certain discrete frequencies, whose values are governed by a mechanism involving the periodic shedding of vorticity from the leading edge of the aperture and feedback of pressure disturbances produced by interaction of the vorticity with the downstream edge. Admissible frequencies are identified with the real parts of complex characteristic frequencies of the linearized equation of motion of the vortex sheet. These eigenfrequencies are also poles of the Rayleigh conductivity of the aperture, and their dependence on the mean velocity ratio across the aperture is calculated for the first four ‘operating stages’ of the motion. Results are presented in both graphical and tabular forms to facilitate their ready incorporation into numerical models of more complicated flow problems. The investigation completes the linearized study of this problem initiated by Scott (1995), which dealt with forced, time–harmonic oscillations of the shear layer.

Numerical Prediction of Exhaust Fan Tone Noise from High Bypass Aircraft Engines

The ability to accurately predict fan noise is important in designing and optimizing aircraft engine turbofans for low noise emissions. In this paper, a prediction methodology for exhaust fan tone noise analysis is described and validated against various canonical test cases and NASA Source Diagnostic Test (SDT) data. The prediction process consists of solving Reynolds-Averaged Navier-Stokes (RANS) equations to compute the fan wake, and calculating the acoustic response of the outlet guide vanes (OGV) to the fan wake using linearized Euler equations. Very good agreement is observed between numerical predictions and semi-analytical results for canonical cases. Detailed comparisons against SDT data are presented for unsteady vane pressure and integrated in-duct exhaust noise power levels. Geometric trends for different OGV configurations at various operating conditions are also analyzed.

INVERSE AEROACOUSTIC PROBLEM FOR A RECTANGULAR WING IN A GUST t

The feasibility of an inverse aeroacoustic problem, where the pressure on a thin, flat, rigid rectangular wing in unsteady, subsonic flow is predicted from the farfield acoustic signal, is investigated. The decaying nature of radiation phenomena renders the inverse problem ill-posed because small discrepancies in the farfield are amplified in the nearfield. The resulting ill-conditioned system is solved using the Singular Value Decomposition which generally requires cut-off or regularization techniques to discard redundant or unphysical information. However, an algorithm is developed for optimally determining the nearfield pressure without relying on the user input of a threshold parameter. Tests using numerically generated input data show the inversion is feasible and accurate for sufficiently accurate input data. For low Mach numbers and low-to-moderate reduced frequencies, the inversion remains feasible when error is introduced in the farfield measurements.

Wet Compression Effects on Axial Compressor Performance Using Pitch-Line Models

The impact of wet compression technology on compressor performance is studied using a coupled water-evaporation-pitch-line numerical model. The model uses an iterative approach to compute the modified flow conditions at blade-row stations due to inter-stage evaporation of water droplets introduced at the compressor inlet. The evaporation rate predicted by the model is compared with experimental data for stationary droplets in a duct. Performance predictions are compared with data for a GE-proprietary compressor. Study of various water droplet sizes and various water-to-air mass ratios is discussed.Copyright

Aeroacoustic predictions of a wing-flap configuration in three dimensions

The preliminary investigation of an efficient method for predicting the aeroacouatic performance of high-lift wing configurations le presented. An unsteady pane1 code is used to solve for the velocity potential on the surface of the wing assuming that the flow is inviscid, subsonic, isentropic, and irrotational off the surfaces of the wing and wakes. The unsteady Kutta condition is used to mode1 the shedding of vorticity from the sharp trailing edges of the main element and the flap. The surface potential is then used as input to evaluate the acoustic signal in the far fleld. The method was applied to a simple rectangular wing and flap geometry subjected to impuleively started flow. A prediction for the increase in total radiated acoustical energy with increasing flap deflection angle was quantifled as a preliminary demonstration of the capabilit& of the propoeed method.