Aerodynamic Measurements of a Gulfstream Aircraft Model With and Without Noise Reduction Concepts

Abstract

Steady and unsteady aerodynamic measurements of a high-fidelity, semi-span 18% scale Gulfstream aircraft model are presented. The aerodynamic data were collected concurrently with acoustic measurements as part of a larger aeroacoustic study targeting airframe noise associated with main landing gear/flap components, gear-flap interaction noise, and the viability of related noise mitigation technologies. The aeroacoustic tests were conducted in the NASA Langley Research Center 14-by 22-Foot Subsonic Wind Tunnel with the facility in the acoustically treated open-wall (jet) mode. Most of the measurements were obtained with the model in landing configuration with the flap deflected at 39º and the main landing gear on and off. Data were acquired at Mach numbers of 0.16, 0.20, and 0.24. Global forces (lift and drag) and extensive steady and unsteady surface pressure measurements were obtained. Comparison of the present results with those acquired during a previous test shows a significant reduction in the lift experienced by the model. The underlying cause was traced to the likely presence of a much thicker boundary layer on the tunnel floor, which was acoustically treated for the present test. The steady and unsteady pressure fields on the flap, particularly in the regions of predominant noise sources such as the inboard and outboard tips, remained unaffected. It is shown that the changes in lift and drag coefficients for model configurations fitted with gear/flap noise abatement technologies fall within the repeatability of the baseline configuration. Therefore, the noise abatement technologies evaluated in this experiment have no detrimental impact on the aerodynamic performance of the aircraft model.

Aeroacoustic Evaluation of Flap and Landing Gear Noise Reduction Concepts

“…The aerodynamic performance (including stall conditions) of the 18% scale model with the flap and gear noise reduction concepts installed is discussed in the companion paper by Neuhart et al 13 In that paper, the authors show that the changes in lift and drag coefficients for model configurations fitted with gear/flap noise abatement technologies fall within the repeatability of the baseline configuration. Thus, the concepts have no measurable detrimental impact on the aerodynamic performance of the aircraft model.…”

“…The roughened surface may significantly thicken the turbulent boundary layer on the floor, thus affecting the aeroacoustic measurements. The effects of the acoustic floor on the aerodynamic characteristics of the 18% model are discussed in detail in the companion paper by Neuhart et al 13 Note, however, that the steady and unsteady pressure fields on the flap, particularly in the regions of predominant noise sources (inboard and outboard flap tips), remained unaffected.…”

“…We present sample comparisons of power spectral density levels for configurations without and with noise reduction concepts applied to the flap and main landing gear. Details of the aerodynamic data measured concurrently during the second entry and off-surface PIV measurements acquired during the third entry, are given in companion papers by Neuhart et al 13 and Yao et al 14 respectively.…”

Towards Full Aircraft Airframe Noise Prediction: Lattice Boltzmann Simulations

“…10 The second 14x22 tunnel entry was executed in two segments. The first segment was dedicated to simultaneous acoustic and surface pressure measurements, 11,12 while the second segment was devoted to off-surface flow measurements for the nominal aircraft landing configuration. 13 Concurrent with the experimental test campaigns, there is a comprehensive computational effort aimed at extending the state-of-the-art in airframe noise prediction capabilities from component-level to full aircraft systemlevel configurations.…”

An Assessment of Flap and Main Landing Gear Noise Abatement Concepts

“…Using a high-fidelity 18% scale, semi-span model of a Gulfstream aircraft as a test bed, numerous noise abatement technologies targeting the sources associated with flap tips and main landing gear were evaluated. 12,13 The aeroacoustic performance and effectiveness of the noise mitigation concepts were demonstrated via microphone array measurements with the aircraft model in a landing configuration with the flap deflected 39º and the main landing gear installed (on) or removed (off). Data were acquired at Mach numbers of 0.16, 0.20, and 0.24 over directivity angles spanning 56º and 116º, with 90º representing the overhead direction.…”