noise from forced mixers

7/30/2019 Noise from Forced Mixers

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Noise from Forced Mixers

Funded by the Indiana 21st

Century Research andTechnology Fund


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Correlating RANS Computed

Mean Flow with Forced Mixed

Jets

C. Wright, G. Blaisdell, A. Lyrintzis

School of Aeronautics & Astronautics

Purdue University


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Goals of Project

The primary goal is to develop a greater

understanding of the how noise from

forced mixed jets may be correlated to the

RANS calculated mean flow field.

The ultimate goal is to develop quantitative

correlations that could be used as input for

a semi-empirical model


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Approaches

Careful selection of numerical tools such as theturbulence model and CFD code are veryimportant. Validation should concentrate on adetailed comparison of flow contours rather thanintegrated quantities.

Grid development and validation should likewiseconcentrate on the details of the flow.

Qualitative trends and observations regardingthe relationship between noise data and CFDresults should be investigated before attemptingto quantify the results.


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Internally Forced Mixed Jet

By

pass

Flow

Mixer

Core

Flow

Nozzle

Tail Cone

Exhaust

Flow

Exhaust / Ambient

Mixing Layer

Lobed Mixer

Mixing Layer


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Forced Mixer

H

Lobe Penetration

(Lobe Height)

H:


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3-D Mesh


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WIND Code options

2nd order upwind scheme

1.7 million/7 million grid points

8-16 zones 8-16 LINUX processors

Spalart-Allmaras/ SST turbulence model

Wall functions


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Grid Dependence

1.7 million grid points 7 million grid points

Density

Vorticity

Magnitude


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Spalart-Allmaras and and Menter SST at

Nozzle Exit PlaneSpalart SST

Density

Vorticity

Magnitude


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Vorticity Magnitude at Nozzle Exit

( Scale Geometry)

Low Penetration Mid Penetration High Penetration


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Turbulent Kinetic Energy at Nozzle Exit

( Scale Geometry)Low Penetration Mid Penetration High Penetration


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High Penetration Mixer Flowfield

Case is for a high throttlesetting at Mach 0.2

Used Menter SSTTurbulence Model

Good overall agreementwith experiment. TKE is alittle low for X/D = 1.0 andX/D = 2.0. CFD resultstend to be overly sharp anddefined.

CFD and experiment bothshow a substantial amountof interaction between thefree shear layer and thestreamwise vortices.


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Medium Penetration Mixer Flowfield

Case is for a high throttlesetting at Mach 0.2

Used Menter SSTTurbulence Model

The agreement between theCFD and the experiment isabout the same as for thehigh penetration case.

The free shear layer and thestreamwise vortices exist asseparate and distinct flowstructures through at leastX/D = 1.0.


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Experimental Results (1/4 Scale Model)


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Experimental Results (1/4 Scale Model)


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Current State of Project

Finishing up CFD runs. Using WIND and MenterSST turbulence model.

Currently studying noise data along with RANS

results and PIV experiments (including lowpenetration case not shown).

Have identified some interesting trends, and arepreparing more CFD runs to finalize these

comparisons. Specifics of research is being published in a

paper for the AIAA Reno conference (Jan. 2004).


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Development of a Semi-EmpiricalJet Noise Model for Forced Mixer

Noise Predictions

L. Garrison, Purdue University

W. Dalton, Rolls-Royce Indianapolis

A. Lyrintzis and G. BlaisdellPurdue University


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Four-Source Model Comparisons Four-Source method implementation

Predictions for the confluent mixer

Two-Source Model Formulation

Optimization procedure

Optimized results for the 12 lobe mixers

Optimized parameter correlations

Outline


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Practical Configuration Geometry

Secondary Flow

Primary Flow

Flow Mixer

Nozzle Wall

Tail Cone

(Bullet)

Final Nozzle Exit


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Dual Flow Configurations

Four-Source method

developed for acoplanar, coaxial jet

The configuration for the

practical case has a

buried primary flow in a

convergent nozzle with a

center body (tail cone orbullet)


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Based on an Equivalent Coaxial Jet

Approach developed by B. Tester and M.Fisher

Define primary and secondary jets at the

final nozzle exit plane Assumptions

Isentropic flow in the nozzle

Primary and secondary flows do not mix in thenozzle

Static pressure of the two flows at the exitplane are equal

Single Jet Property Calculation


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Single Jet Property Calculation

Jet Areas at the Final Nozzle Exit

GuessAp

CalculateAs

Calculate Mexit

Calculate Pstatic

Iterate until the primary and secondary static

pressures are equal

pns AAA

121

2

2

1

2

2

1

1

1

cs

exit

exit

cs

cs

exit

M

M

M

M

A

A

12

2

11

exit

static

oM

P

PJ


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Four-Source Method Implementation Primary and Secondary Jet Properties

Calculated at the final nozzle exit

Mixed Jet and Effective Jet Properties

1

1TT

1

))(1(1DD

1

1VV

pm

2

1

2pm

2

pm

p

s

p

s

p

s

A

A

V

V

pe

1/22

pe

pe

TT

1DD

VV

7dBe


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Current Prediction Method Comparisons

Four-Source / Single Jet / Experimental

Data Comparisons Confluent Mixer, Low Power Operating Point

ARP876C Method used for all single jetnoise predictions

Bass and Sutherland correction for atmosphericattenuation

Four-Source coaxial jet prediction Based on equivalent coaxial jet properties

Single jet prediction Based on fully mixed flow at the final nozzle exit


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Current Prediction Method Comparisons


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Forced Mixer Experimental Data

Four Mixer Configurations

Confluent Mixer (CFM)

Low Penetration 12 Lobe Mixer (12CL)

Mid Penetration 12 Lobe Mixer (12UM)

High Penetration 12 Lobe Mixer (12UH) Low Power Operating Point

H


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Forced Mixer Experimental Data


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Objective:

Match the experimental data SPL spectrum at all

angles and all frequencies using two single stream

jet sources.

Formulation:

s s s s 1 s0 USPL ( , ) SPL(V ,T ,D , , ) 10lo Bg ( dF , )cf ff f

Single Jet

Prediction

Source

Strength

Spectral

Filter

Variable Parameters:

m m m m 1 m0 DSPL ( , ) SPL(V ,T ,D , , ) 10lo Bg ( dF , )cf ff f

s m

Spectral Filter Cut-off Frequency

, Source StrengtdB hs )d BB (d

cf

Two-Source Model


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Two-Source Model

dB

dB

fc

fc

Variable Parameters

1/3 Octave Band Number 1/3 Octave Band Number

1/3OctaveSP

L[dB]

1/3OctaveSP

L[dB]

Effects of Variations in dB Effects of Variations in fc


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Optimization Procedure For a given geometry and operating condition,optimize the source strength parameters

(dbs, dbm) for a range of cut-off frequencies

Find the set of optimized parameters that

minimize the prediction error for all operating

conditions

Correlate the final set of parameters to the

changes in the mixer design

Two-Source Model Optimization


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Optimization Challenges

Optimum Criterion Maximum Error

Average Error

Weighted Error

Solution Non-Uniqueness Local Minima

Non-Linear Behavior

Optimization Tools

Nonlinear Least Squares

MATLAB: lsqnonlin (LevenbergMarquadt Optimization

Method )



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15 Microphone locations (90 to 160 in 5 increments)

1 Sound Pressure Level (SPL) spectrum per microphone

27 Frequency Bands per spectrum (1/3 Octave Bands)

405 SPL values per data point

Microphone Locations

Jet80observer

J

r

D


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Optimum Criterion

Based on a OASPL type weighting

At each observer angle:

Weighted error values:

exp exp

max

0.1 SPL , SPL ,

, 10i if f

w iE f

, , , ,w exp pred Error f E f SPL f SPL f


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Two-Source Model Results Test Case

Low Penetration Mixer Low Power Operating Point

Two-Source Model Upstream Source: Secondary Jet

Downstream Source: Mixed Jet

Prediction

Method

Maximum

Error [dB]

Average

Error [dB]

Weighted

Error [dB]

Four-Source 13.18 2.56 0.41

Single Jet 12.02 2.53 0.64

Two-Source 8.35 1.29 0.36

O ti i d T S R lt


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Optimized Two-Source Results


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Optimized Two-Source Results


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Current jet noise predictions do notaccurately model the noise from jets withinternal forced mixers

Forced mixer jet noise can be modeled by

a combination of two single jet sources Optimized Two-Source model source

strengths and cut-off Strouhal numbersappear to correlate linearly with theamount of lobe penetration

Summary


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Fisher, M.J., Preston, G.A., and Bryce, W.D., A Modelling of the

Noise from Simple Coaxial Jets Part I: With Unheated PrimaryFlow, Journal of Sound and Vibration, 209(3):385-403, 1998

Fisher, M.J., Preston, G.A., and Mead, C.J., A Modelling of the

Noise from Simple Coaxial Jets Part II: With Heated Primary Flow,

Journal of Sound and Vibration, 209(3):405-417, 1998

ARP87C: Gas Turbine Jet Exhaust Noise Prediction, Society ofAutomotive Engineers, Inc., November, 1985.

Bass, H.E., Sutherland, L.C., Zuckerwar, A.J., Blackstone, D.T., and

Hester, D.M., Atmospheric Absorption of Sound: Further

Developments, Journal of the Acoustical Society America,

97(1):680-683, 1995

References


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SPLexp - SPLpredSPLexpSPLexpmax

noise from forced mixers

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