cfd analysis of chevron nozzle

National Aeronautics and Space Administration

www.nasa.gov

Computational Analysis of a Chevron Nozzle UniquelyTailored 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 PaoNASA Langley Research Center

andVinod G. MengleBoeing 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 FeaturesOn Typical Conventional Aircraft

Nacelle-airframe integratione.g. chines, flow distortion,relative angles Jet-pylon

interaction of thePAA T-fan nozzle

Jet-flapimpingement

Jet-flap trailingedge interaction

Jet influence onairframe sources:side edges

Jet interaction withhorizontal stabilizers

Jet and fan noisescattering fromfuselage, wing, flapsurfaces

Pylon-slat cutout

QTD2 partnership ofBoeing, GE, Goodrich,NASA, and ANA


Objectives

To build a predictive capability to link geometryto noise for complex configurations

To identify the flow and noise sourcemechanisms of the PAA T-Fan (quieter at takeoff 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 Lighthills Acoustic Analogy in 3D

Models the jet flow with a fictitious volume distributionof quadrupole sources radiating into a uniform ambientmedium

Uses RANS CFD as input

Now implemented for structured and unstructuredgrids (ref AIAA 2006-2597)


Sample Grid Plane

31 Million Cells for 180o

PAB3D solution: 33hours on 44 ColumbiaCPUs (Itanium 2)

Jet3D solution, 10minutes on Mac


Model Scale LSAF PAA Nozzles Analyzed

Four Nozzles Chosen forAnalysis:

Axisymmetric Nozzle(not an experimentalnozzle)

bb conventional nozzles

RR state-of-the-artazimuthally uniformchevrons on core andfan

RT PAA T-fanazimuthally varyingchevrons on fan anduniform chevrons oncore

For more details seeMengle et al. AIAA 06-2467


Generic Pylon Effect Understanding - AIAA 05-3083

Core Flow Induced Off of Jet Axis byCoanda Effect

Pairs of Large Scale Vortices Created TKE and Noise Sources Move

Upstream Depending on Design Details can

Result in Noise Reduction or Increasewith Pylon

Refs: AIAA 01-2183, 01-2185, 03-3169, 03-3212, 04-2827, 05-3083


Analysis Procedure

Start with established facts and work fromderived to fundamental quantities to formconnections 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 20062467

Tunnel noise

bb predicted within 1 dB forwhole range

RR over predicted by 1 dB forfrequencies < 10 kHz, underpredicted by up to 2 dB forhigh frequencies

RT predicted within 1 dB forwhole range, under predictedhigh frequencies

Trends predictedcorrectly increasingconfidence of flowand noise sourcelinkage


Noise Prediction CFD Link

Noise and TKE sources relative to Axi are consistent with previouspylon 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 noisesources correspondwith peak TKE

Local noiseincreased bychevron length

Cross flow streamlines show shearlayer vorticityorientation


Beginning Fan/Core Shear Merger

Noise and TKE peakas layers merge

RR levels slightlylower than bb

RT merger delayed,much lower levels

Axi noiseasymmetry due toLAA observerlocation. TKE issymmetric

Axial velocity 20times stronger thancross flow, thusstrongest vortexwould take about60D for onerevolution

Axi bb RR RT


Peak Noise From Shear Merger

bb, RR peak shown;RT peaks 0.5D later,one contour lowerthan bb and RR

Unmerged Axi withlower noise and TKE,but will persist moredownstream

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 moredefined on top, lesson bottom due tochevron length

Vertical velocitycomponent showseffect of pylon oncross flow:

Axi shows Coandaeffect on plug

Pylon cases haveexpanded downwardflow region to getaround pylon to fillin plug

Less downwardmovement in fanflow for RT


Consolidation and Entrainment

Core and fan shearlayer vorticityconsolidates to formvortex pair

RR vortex pairslightly strongerthan bb

RT vortex pairsignificantly weakerthan bb and RR


T-Fan Reduces Overall Mixing

RT local mixingproportional tochevron length

RT decreases netmixing, extends coreby ~ 1/2 D

RR negligible mixingover bb


Overall Jet Trajectory

bb and RR equivalent symmetric chevron does notinteract with pylon effect

RT showing less downward movement favorableinteraction of asymmetric chevron with pylon effect

Total Temperature Centroid


Summary

Overall mixing does not vary much between bb, RRand 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 foundcomputationally


Concluding Remarks

A predictive capability linking geometry to noisehas been demonstrated

The T-Fan benefits from a favorable interactionbetween asymmetric chevrons and the pylon effect


Discussion, Extra Slides


Axisymmetric Nozzle

Surfaces colored by temperature


Baseline Nozzle (bb)

Fan boundarystreamline

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 theintegration 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 oruse integration to reduce net radiated noise.


PAA on QTD2: Concept to Flight in Two Years

Exploration of Possible PAA Concepts withQTD2 Partners (5/03 4/04)

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

(AIAA 05-3083, 06-2436)

PAA Experiment at Boeing LSAF9/04

PAA Effects and Noise ReductionTechnologies Studied

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

PAA T-Fan ChevronNozzle

PAA EffectsInstrumentation

AIAA 06-2438, 06-2439


Grid Coarse in Radial Direction


Grid Cause of Vorticity Lines


Detailed PAA FlowAnalysis

Begin with Highly ComplexLSAF Jet-Pylon NozzleGeometries

JET3D Noise SourceMap Trends Validatedwith LSAF PhasedArray Measurements

JET3D Validation of SpectraTrend at 90 degrees

Develop Linkages ofcomplex flow and noisesource interactions

Three major effects tounderstand:

Pylon effect Chevron effect PAA T-fan effect and their interaction

PAA Analysis Process to Develop Understanding of PAA T-fanNozzles Flow/Noise Source Mechanisms

cfd analysis of chevron nozzle

Documents

noise reduction

geometryto noise

noise sourcemechanisms

jet flow

noise sources moveupstream

jet3d solution

core flow

paa tfan quieter