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Research Papers

Drag Management in High Bypass Turbofan Nozzles for Quiet Approach Applications

[+] Author and Article Information
P. Shah

Senior Project Engineer

A. Robinson

Project Engineer

A. Price

Engineer
ATA Engineering, Inc.
San Diego, CA 92130

Z. Spakovszky

Professor of Aeronautics and Astronautics
Massachusetts Institute of Technology,
Cambridge, MA 02139

The current definition does not include the rematching of gas turbine components when the device is deployed.

The polar array microphones were, thus, >55 fan exit diameters away.

Prismatic vanes were designed to produce a desired outflow rather than represent a deployed EAB mechanism.

The CRJ installation was chosen because there are examples of both internal (CRJ-200) and external (CRJ-900) plug configurations.

Observation 2 is found to be in accord with the substitution principle of Munk and Prim [19], also discussed in Greitzer et al. [20], which states that two inviscid flowfields with identical stagnation pressure distributions but differing stagnation temperature distributions will produce identical Mach number and static pressure distributions.

Cd,eq was defined as a net thrust reduction per Eq. 1 and was evaluated in CFD based on a control volume that accounts for both gross thrust, ram drag, and nacelle exterior drag.

The swirl angle at the fan exit plane is lower than the swirl angle prescribed at the inlet of the fan stream in the CFD domain. This is due to conservation of angular momentum because the streamtube radius and area both contract at the fan exit. The axial velocity increases faster than the tangential velocity, resulting in a lower swirl angle. In this paper, configurations are identified by vane turning angles, not fan nozzle exit swirl angles.

Bypass ratios are lower than the nozzle design values because the core flow was cold and, hence, had higher density than hot core flows.

The ANOPP noise module for elevon noise was not available. This source is a significant contributor to hybrid wing-body approach noise—the results for this aircraft are, therefore, conservative because greater noise reduction would be predicted when elevon noise is included.

Steep approach is not necessarily applicable to certification, but the example is given here due to its simplicity. Certification scenarios might include slower or aeroacoustically cleaner approach at standard glideslope angle.

The tube-and-wing analysis assumes that the generation of swirl will have little effect on fan exhaust (discharge) noise, which is the dominant source in the aft emission direction for this aircraft. If this source were affected by the presence of swirl, a similar selective use of the EAB during approach to the observer may be one way to mitigate any adverse noise impact.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received December 20, 2012; final manuscript received February 18, 2013; published online September 26, 2013. Editor: David Wisler.

J. Turbomach 136(2), 021009 (Sep 26, 2013) (13 pages) Paper No: TURBO-12-1250; doi: 10.1115/1.4023908 History: Received December 20, 2012; Revised February 18, 2013

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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References

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Weed, P., 2010, “Hybrid Wing-Body Aircraft Noise and Performance Assessment,” M.S. thesis, MIT, Cambridge, MA.
Shah, P. N., Mobed, D., and Spakovszky, Z., 2007, “Engine Air-Brakes for Quiet Air Transport,” 45th AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, January 8–11, AIAA Paper No. 2007-1033. [CrossRef]
Shah, P. N., 2010, “A Novel Turbomachinery Air-Brake Concept for Quiet Aircraft,” ASME J. Turbomach., 132(4), p. 041002. [CrossRef]
Shah, P. N., Mobed, D., Spakovszky, Z. S., Brooks, T. F., and Humphreys, W. M., 2010, “Aeroacoustics of Drag Generating Swirling Exhaust Flows,” AIAA J., 48(4), pp. 719–737. [CrossRef]
Brooks, T., and Humphreys, W., Jr., 2006, “A Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) Determined From Phased Microphone Arrays,” ASME J. Sound Vib., 294(4–5), pp. 856–879. [CrossRef]
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Schwartz, I., 1973, “Jet Noise Suppression by Swirling in the Jet Flow,” AIAA Aero-Acoustics Conference, Seattle, WA, October 15–17, AIAA Paper No. 1973-1003. [CrossRef]
Janardan, B. A., Hoff, G. E., Barter, J. W., Martens, S., Gliebe, P. R., Mengle, V., and Dalton, W. N., 2000, “AST Critical Propulsion and Noise Reduction Technologies for Future Commercial Subsonic Engines: Separate-Flow Exhaust System Noise Reduction Concept Evaluation; Final Report,” NASA CR 2000-210039.
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Figures

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Fig. 1

Engine air-brake technology development stages

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Fig. 2

4BB internal plug dual-stream nozzle

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Fig. 3

5BB external plug dual-stream nozzle

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Fig. 4

4BB cross section. Image adapted from Ref. [16].

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Fig. 5

5BB cross section. Image adapted from [16].

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Fig. 6

Aft-looking-forward view of NATR with upper polar array and lower sideline array locations shown

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Fig. 7

Computer-aided design (CAD) models of select experimental hardware shown against 4BB cross section. (a) New vaneless hub flowpath (VKNN-NOPY). (b) Periodically spaced 60 deg vanes (VK60-NOPY). (c) Straight pylon with new hub flowpath (VKNN-STPY). (d) Deflected trailing edge pylon with forward asymmetric visk (VKFA-DNPY). (e) Deflected trailing edge pylon with fence structure and rear (fan nozzle exit) asymmetric visk (VKRA-DFPY).

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Fig. 8

Overview of CFD domain and mesh (4BB geometry shown). (a) Mesh topology in nozzle region. Freestream, fan and core inlet boundary conditions specified as shown. (b) Turbomachinery mesh for swirl vane implementation.

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Fig. 9

Mach number contours for axisymmetric 4BB cold core flow simulations. Swirl prescribed at fan inlet.

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Fig. 10

Mach number contours for axisymmetric 5BB cold core flow simulations. Swirl prescribed at fan inlet.

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Fig. 11

Gray streamlines and Mach contours in horizontal isoplane for VKRA-DFPY configuration

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Fig. 12

CFD-predicted Cd,eq is strongly correlated to fan exit swirl angle. Fan diameter-based Aref.

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Fig. 13

Correlation between fan flow reduction and Cd,eq based on fan (circular) area for 4BB cases

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Fig. 14

Correlation between core flow reduction and Cd,eq based on fan (circular) area for 4BB cases

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Fig. 15

DAS beamforming images of dominant noise source for three frequency bands and three levels of swirl (rows: 0 -, 40 -, and 60-deg simple swirl visks)

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Fig. 16

RANS CFD-predicted turbulent kinetic energy contours support the general observation that the dominant region of noise generation moves forward with swirl. FNPR = 1.191, CNPR = 1.209, and M = 0.212. Both streams are cold.

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Fig. 17

1-foot lossless one-third-octave SPL spectra at 90-deg observer position for various 4BB simple visk configurations; FNPR = 1.27, CNPR = 1.33

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Fig. 18

1-foot lossless OASPL directivity for various 4BB simple visk configurations; FNPR = 1.27, CNPR = 1.33

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Fig. 19

1-foot lossless one-third-octave SPL spectra at 90-deg observer position for various 5BB simple visk configurations; FNPR = 1.27, CNPR = 1.33

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Fig. 20

1-foot lossless OASPL directivity for various 5BB simple visk configurations; FNPR = 1.27, CNPR = 1.33

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Fig. 21

1-foot lossless one-third-octave SPL spectra at 90-deg observer position for various 4BB pylon configurations; FNPR = 1.27, CNPR = 1.33

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Fig. 22

1-foot lossless OASPL directivity for various 4BB pylon configurations; FNPR = 1.27, CNPR = 1.33

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Fig. 23

DAS beamforming images of VKNN-NOPY, VK40-NOPY, and VKRA-DFPY configurations at 3150 Hz

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Fig. 24

Single-aisle, twin-engine aircraft (737-800 class) PNLT time history for conventional and EAB operation for 50-deg swirl vanes that generate Cd,eq = 1.05 and 13.6 dB jet noise penalty at FNPR = 1.27

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Fig. 25

Generic hybrid wing/body PNLT time history for conventional and EAB operation for 40-deg vanes, which generate Cd,eq = 0.57 and 5.4 dB jet noise penalty at FNPR = 1.27

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