Aeroacoustics of Drag-Generating Swirling Exhaust Flows

Shah, Parikshit; Mobed, D. D.; Spakovszky, Z. S.; Brooks, Thomas F.; Humphreys, William M.

doi:10.2514/1.37249

Cited by 5 publications

(6 citation statements)

References 16 publications

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“…Section III describes the EAB visk and pylon designs and experimental hardware that was fabricated, and briefly summarizes key findings from an aerodynamic flowfield assessment using CFD 4 . Section IV describes the test facility.…”

Section: Background and Motivationmentioning

confidence: 99%

“…The EAB concept was demonstrated experimentally in a simple ram-pressure-driven nacelle with swirl vanes to generate a throughflow-area-based drag coefficient of 0.83 with a relatively imperceptible noise signature ( [3], [4]). Vortex breakdown was found to be a limiting phenomenon, with rapid expansion of the vortex core near the duct exit resulting in a sudden noise increase of over 15 dB.…”

Section: Background and Motivationmentioning

confidence: 99%

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Aeroacoustics of Swirling Exhaust Flows in High Bypass Ratio Turbofan Nozzles for Drag Management Applications

Shah

Spakovszky

2011

17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference)

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The aeroacoustics of swirling exhaust flows in high bypass ratio turbofan nozzles are assessed for aircraft approach drag management applications. Aerodynamic designs of swirl vane hardware were tested in an anechoic jet test facility to quantify their thrust reduction (or equivalent drag generation) capability and noise. Simple vaned-disk (visk) hardware using a row of periodically spaced swirl vanes was used to study flow interactions and noise generation mechanisms associated with swirl generated in the bypass duct. The swirling bypass exhaust stream creates suction on the core stream, which elevates the core flow and decreases the bypass ratio by up to 40 percent for the geometries tested. Swirling the bypass exhaust enhances mixing, and phased array measurements suggest that the apparent noise source moves upstream and radially inward toward the inner shear layer, and radiates preferentially in the direction of swirl. The presence of a pylon with a deflected trailing edge and asymmetric swirl vanes is found to produce a coherent swirling outflow with slightly greater noise generation than its idealized counterpart. The relationship between gross thrust reduction and noise generation is quantified and applied to a simple steep approach noise simulation at fixed aircraft speed. Results suggest a noise reduction potential of up to 3.1 dB, tonecorrected peak perceived noise level (PNLT) and 1.8 dB effective perceived noise level (EPNL) for a single-aisle, twin engine aircraft. NomenclatureRoman a ∞ = Freestream sound speed A ref = Reference (total fan circular) area C d,eq = Equivalent drag coefficient CNPR = Core nozzle pressure ratio D b = Fan (bypass) nozzle exit diameter FNPR = Fan (bypass) nozzle pressure ratio F gross = Gross thrust F net = Net thrust M B = Ideal bypass-stream Mach number M C = Ideal core-stream Mach number M MA = Ideal mass-averaged Mach number M ∞ = Freestream (approach) Mach number V app = Freestream approach velocity Greek ρ = Density θ app = Approach glideslope angle

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Section: Background and Motivationmentioning

confidence: 99%

Section: Background and Motivationmentioning

confidence: 99%

Aeroacoustics of Swirling Exhaust Flows in High Bypass Ratio Turbofan Nozzles for Drag Management Applications

Shah

Spakovszky

2011

17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference)

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“…Figure 1 presents a technology development roadmap for the development of the EAB that is discussed in this paper. As shown in the lower-left portion of the figure, generation of a swirling outflow from the engine's propulsion system to reduce approach thrust was originally proposed by Shah et al [18]- [20]. Low-TRL proof of concept was demonstrated experimentally in a simple ram-pressure-driven nacelle with swirl vanes (a "swirl tube") to generate drag quietly.…”

Section: Equationmentioning

confidence: 99%

Full-Scale Turbofan Demonstration of a Deployable Engine Air-Brake for Drag Management Applications1

Pfeiffer

Davis

Hartley

et al. 2017

Journal of Engineering for Gas Turbines and Power

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This paper presents the design and full-scale ground-test demonstration of an engine air-brake (EAB) nozzle that uses a deployable swirl vane mechanism to switch the operation of a turbofan's exhaust stream from thrust generation to drag generation during the approach and/or descent phase of flight. The EAB generates a swirling outflow from the turbofan exhaust nozzle, allowing an aircraft to generate equivalent drag in the form of thrust reduction at a fixed fan rotor speed. The drag generated by the swirling exhaust flow is sustained by the strong radial pressure gradient created by the EAB swirl vanes. Such drag-on-demand is an enabler to operational benefits such as slower, steeper, and/or aeroacoustically cleaner flight on approach, addressing the aviation community's need for active and passive control of aeroacoustic noise sources and access to confined airports. Using NASA's Technology Readiness Level (TRL) definitions, the EAB technology has been matured to a level of 6, i.e., a fully functional prototype. The TRL-maturation effort involved design, fabrication, assembly, and ground-testing of the EAB's deployable mechanism on a full-scale, mixedexhaust, medium-bypass-ratio business jet engine (Williams International FJ44-4A) operating at the upper end of typical approach throttle settings. The final prototype design satisfied a set of critical technology demonstration requirements that included (1) aerodynamic equivalent drag production equal to 15% of nominal gross thrust in a high-powered approach throttle setting (called dirty approach), (2) excess nozzle flow capacity and fuel burn reduction in the fully deployed configuration, (3) acceptable engine operability during dynamic deployment and stowing, (4) deployment time of 3-5 seconds, (5) stowing time under 0.5 second, and (6) packaging of the mechanism within a notional engine cowl. For a typical twin-jet aircraft application, a constant-speed, steep approach analysis suggests that the EAB drag could be used without additional external airframe drag to increase the conventional glideslope from 3 to 4.3 degrees, with about 3 dB noise reduction at a fixed observer location.

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“…Figure 1 presents a roadmap of the increasing complexity that is being addressed in the current EAB design effort. Generation of a swirling outflow from the engine's propulsion system to reduce approach thrust has been proposed in previous work [7][8][9]. While the EAB concept was demonstrated experimentally in a simple ram pressure-driven nacelle with swirl vanes to generate drag quietly, the challenge of implementation in a real engine environment was left unanswered.…”

Section: Introductionmentioning

confidence: 99%

“…Beyond a swirl vane angle of about 50 deg, the flowfield was found to transition from stable swirling flow to unsteady vortex breakdown near the duct exit. Far-field noise and source mechanisms were rigorously dissected [9] using a "deconvolution approach for the mapping of acoustic sources" (DAMAS) phased array measurement technique [10] in the NASA Langley Quiet Flow Facility (QFF). The measured swirl-drag-noise relationship was found to depart from that of other drag generators, with vortex breakdown being the controlling phenomenon.…”

Section: Introductionmentioning

confidence: 99%

Drag Management in High Bypass Turbofan Nozzles for Quiet Approach Applications

Shah

Robinson

Price

et al. 2013

Journal of Turbomachinery

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The feasibility of a drag management device that reduces engine thrust on approach by generating a swirling outflow from the fan (bypass) nozzle is assessed. Deployment of such “engine air-brakes” (EABs) can assist in achieving slower and/or steeper and/or aeroacoustically cleaner approach profiles. The current study extends previous work from a ram air-driven nacelle (a so-called “swirl tube”) to a “pumped” or “fan-driven” configuration and also includes an assessment of a pylon modification to assist a row of vanes in generating a swirling outflow in a more realistic engine environment. Computational fluid dynamics (CFD) simulations and aeroacoustic measurements in an anechoic nozzle test facility are performed to assess the swirl-flow-drag-noise relationship for EAB designs integrated into two NASA high-bypass ratio (HBPR), dual-stream nozzles. Aerodynamic designs have been generated at two levels of complexity: (1) a periodically spaced row of swirl vanes in the fan flowpath (the “simple” case), and (2) an asymmetric row of swirl vanes in conjunction with a deflected trailing edge pylon in a more realistic engine geometry (the “installed” case). CFD predictions and experimental measurements reveal that swirl angle, drag, and jet noise increase monotonically but approach noise simulations suggest that an optimal EAB deployment may be found by carefully trading any jet noise penalty with a trajectory or aerodynamic configuration change to reduce perceived noise on the ground. Constant speed, steep approach flyover noise predictions for a single-aisle, twin-engine tube-and-wing aircraft suggest a maximum reduction of 3 dB of peak tone-corrected perceived noise level (PNLT) and up to 1.8 dB effective perceived noise level (EPNL). Approximately 1 dB less maximum benefit on each metric is predicted for a next-generation hybrid wing/body aircraft in a similar scenario.

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Aeroacoustics of Drag-Generating Swirling Exhaust Flows

Cited by 5 publications

References 16 publications

Aeroacoustics of Swirling Exhaust Flows in High Bypass Ratio Turbofan Nozzles for Drag Management Applications

Aeroacoustics of Swirling Exhaust Flows in High Bypass Ratio Turbofan Nozzles for Drag Management Applications

Full-Scale Turbofan Demonstration of a Deployable Engine Air-Brake for Drag Management Applications1

Drag Management in High Bypass Turbofan Nozzles for Quiet Approach Applications

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