National Aeronautics and Space Administration Computational Analysis of a Chevron Nozzle Uniquely...

National Aeronautics and Space Administration

www.nasa.gov

Computational Analysis of a Chevron Nozzle Uniquely Tailored for Propulsion Airframe Aeroacoustics

12th AIAA/CEAS Aeroacoustics ConferenceCambridge, MAMay 8-10, 2006

Steven J. MasseyEagle Aeronautics, Inc.

Alaa A. ElmiliguiAnalytical Services & Materials, Inc.

Craig A. Hunter, Russell H. Thomas, S. Paul Pao

NASA Langley Research Center

and

Vinod G. Mengle

Boeing Company

May 8, 2006NASA Langley Research Center 2

Outline

• Motivation• Objectives• Numerical Tools• Review of Generic Jet-Pylon Effect• Axi, bb, RR, RT Nozzle Configurations • Analysis Procedure• Results Chain from Noise to Geometry• Summary• Concluding Remarks


General PAA Related Effects and Features On Typical Conventional Aircraft

Nacelle-airframe integration e.g. chines, flow distortion, relative angles

Jet-pylon interaction of the PAA T-fan nozzle

Jet-flap impingement

Jet-flap trailing edge interaction

Jet influence on airframe sources: side edges

Jet interaction with horizontal stabilizers

Jet and fan noise scattering from fuselage, wing, flap surfaces

Pylon-slat cutout

QTD2 partnership of Boeing, GE, Goodrich, NASA, and ANA


Objectives

• To build a predictive capability to link geometry to noise for complex configurations

• To identify the flow and noise source mechanisms of the PAA T-Fan (quieter at take off than the reference chevron nozzle)


Numerical Tools

• PAB3D– 3D RANS upwind code – Multi-block structured with general patching– Parallel using MPI– Mesh sequencing– Two-equation k- turbulence models– Several algebraic Reynolds stress models

• Jet3D– Lighthill’s Acoustic Analogy in 3D

– Models the jet flow with a fictitious volume distribution of quadrupole sources radiating into a uniform ambient medium

– Uses RANS CFD as input

– Now implemented for structured and unstructured grids (ref AIAA 2006-2597)


Sample Grid Plane

• 31 Million Cells for 180o

• PAB3D solution: 33 hours on 44 Columbia CPU’s (Itanium 2)

• Jet3D solution, 10 minutes on Mac


Model Scale LSAF PAA Nozzles Analyzed

Four Nozzles Chosen for Analysis:

• Axisymmetric Nozzle (not an experimental nozzle)

• bb conventional nozzles

• RR state-of-the-art azimuthally uniform chevrons on core and fan

• RT PAA T-fan azimuthally varying chevrons on fan and uniform chevrons on core

For more details see Mengle et al. AIAA 06-2467


Generic Pylon Effect Understanding - AIAA 05-3083

• Core Flow Induced Off of Jet Axis by Coanda Effect

• Pairs of Large Scale Vortices Created

• TKE and Noise Sources Move Upstream

• Depending on Design Details can Result in Noise Reduction or Increase with Pylon

Refs: AIAA 01-2183, 01-2185, 03-3169, 03-

3212, 04-2827, 05-3083


Analysis Procedure

•Start with established facts and work from derived to fundamental quantities to form connections to geometry– Measured noise data (LSAF)– SPL predictions (Jet3D)– OASPL noise source histogram (Jet3D)– Mass averaged, non-dimensional turbulence intensity

(PAB3D)– OASPL noise source maps (Jet3D)– Turbulence kinetic energy (PAB3D)– Axial vorticity– Cross flow streamlines– Vertical velocity– Total temperature– Total temperature centroid– Geometry


Jet3D SPL Predictions with LSAF

*

* Axi case not thrust matched to others

Observer located on a 68.1D radius from the fan nozzle exit at an inlet angle of 88.5 deg. and an azimuthal angle of 180 deg. LSAF data from Mengle et al. AIAA 2006–2467

Tunnel noise

• bb predicted within 1 dB for whole range

• RR over predicted by 1 dB for frequencies < 10 kHz, under predicted by up to 2 dB for high frequencies

• RT predicted within 1 dB for whole range, under predicted high frequencies

Trends predicted correctly increasing confidence of flow and noise source linkage


Noise Prediction – CFD Link

• Noise and TKE sources relative to Axi are consistent with previous pylon understanding of mixing

• Mass-Avg TKE qualitatively matches noise source histogram• bb, RR, RT intersect near x/D = 10• Axi crosses bb, RR at x/D = 12• Axi crosses RT at x/D = 12.75

Jet3D OASPL Histogram PAB3D: Mass-Avg TKE


LAA – CFD Correspondence

Axi bb RR RT

• Peak noise sources correspond with peak TKE

•Local noise increased by chevron length

•Cross flow stream lines show shear layer vorticity orientation


Beginning Fan/Core Shear Merger

• Noise and TKE peak as layers merge

• RR levels slightly lower than bb

• RT merger delayed, much lower levels

• Axi noise asymmetry due to LAA observer location. TKE is symmetric

• Axial velocity 20 times stronger than cross flow, thus strongest vortex would take about 60D for one revolution

Axi bb RR RT


Peak Noise From Shear Merger

• bb, RR peak shown; RT peaks 0.5D later, one contour lower than bb and RR

• Unmerged Axi with lower noise and TKE, but will persist more downstream

Axi bb RR RT


Chevrons Add Vorticity

• Axi cross flow is symmetric, so axial vorticity = zero• bb shows boundary layer vorticity shifted off axis by pylon• RT longer chevrons show increased vorticity over RR and

shorter chevrons on bottom show decreases

Plug

Core Cowl

Pylo

n


Pylon, Plug, Chevron Interaction

• RT fan vortices more defined on top, less on bottom due to chevron length

• Vertical velocity component shows effect of pylon on cross flow:

• Axi shows Coanda effect on plug

• Pylon cases have expanded downward flow region to get around pylon to fill in plug

• Less downward movement in fan flow for RT


Consolidation and Entrainment

• Core and fan shear layer vorticity consolidates to form vortex pair

• RR vortex pair slightly stronger than bb

• RT vortex pair significantly weaker than bb and RR


T-Fan Reduces Overall Mixing

• RT local mixing proportional to chevron length

• RT decreases net mixing, extends core by ~ 1/2 D

• RR negligible mixing over bb

QuickTime™ and aPNG decompressor

are needed to see this picture.

QuickTime™ and aPNG decompressor

are needed to see this picture.


Overall Jet Trajectory

• bb and RR equivalent – symmetric chevron does not interact with pylon effect

• RT showing less downward movement – favorable interaction of asymmetric chevron with pylon effect

Total Temperature Centroid


Summary

• Overall mixing does not vary much between bb, RR and RT and is not indicative of noise in this study

The T-Fan effect:• Varies the strength azimuthally of the localized

chevron vorticity• Reduces the downstream large scale vorticies

introduced by the pylon• Delays the merger of the fan and core shear layers• Reduces peak noise and shifts it downstream• There is the possibility of a more favorable design

for shear layer merger, which can now be found computationally


Concluding Remarks

• A predictive capability linking geometry to noise has been demonstrated

• The T-Fan benefits from a favorable interaction between asymmetric chevrons and the pylon effect


Discussion, Extra Slides…


Axisymmetric Nozzle

Surfaces colored by temperature


Baseline Nozzle (bb)

Fan boundary streamline

Near surface streamlines and temperature


Reference Chevrons (RR)

Slight upward movement



PAA T-Fan Nozzle (RT)


Further upward movement


Motivation

Propulsion Airframe Aeroacoustics (PAA)

• Definition: Aeroacoustic effects associated with the integration of the propulsion and airframe systems.

• Includes: – Integration effects on inlet and exhaust systems – Flow interaction and acoustic propagation effects– Configurations from conventional to revolutionary

• PAA goal is to reduce interaction effects directly or use integration to reduce net radiated noise.


PAA on QTD2: Concept to Flight in Two Years

Exploration of Possible PAA Concepts with QTD2 Partners (5/03 – 4/04)

Extensive PAA CFD/Prediction Work (10/03 – 8/05)

(AIAA 05-3083, 06-2436)

PAA Experiment at Boeing LSAF 9/04

PAA Effects and Noise Reduction Technologies Studied

AIAA 06-2467, 06-2434, 06-2435PAA on QTD2 – 8/05

• PAA T-Fan Chevron Nozzle

• PAA Effects Instrumentation

AIAA 06-2438, 06-2439


Grid Coarse in Radial Direction


Grid Cause of Vorticity Lines


Detailed PAA Flow

Analysis

Begin with Highly Complex LSAF Jet-Pylon Nozzle Geometries

JET3D Noise Source Map Trends Validated with LSAF Phased Array Measurements

JET3D Validation of Spectra Trend at 90 degrees

Develop Linkages of complex flow and noise source interactions

Three major effects to understand:

• Pylon effect

• Chevron effect

• PAA T-fan effect

• and their interaction

PAA Analysis Process to Develop Understanding of PAA T-fan Nozzle’s Flow/Noise Source Mechanisms

National Aeronautics and Space Administration Computational Analysis of a Chevron Nozzle Uniquely...

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