Fundamental Study of Aero Acoustic Emission of Single and Tandem - - PowerPoint PPT Presentation

Slide 1

Fundamental Study of Aero Acoustic Emission of Single and Tandem Cylinder

Winson Lim Tan Chun Hern Voo Keng Soon Vince 05 Nov 12

Slide 2

Brief Review of Flow Over Cylinder

Slide 3

Rationale

• Landing gear system – major contributor to airframe noise during

approach

• Cylinder–like structure includes: Gear main strut, hydraulic lines,

brake pistons, wheels and axles

• Unsteady wake interacts with downstream components to create

dominant noise sources

• Tandem cylinder – simplified prototype
• Models component level interactions
• To understand noise generation mechanism and achieve reduction
• f airframe noise

Slide 4

Wake Characteristics of a Wake Behind a Cylinder

• At very low Re number < 49,

the wake is steady and the wake comprises

• f

two symmetrically placed vortices on each side of the wake

• At higher Re number, the

wake becomes unsteady forming a vortex street as seen in (b)

Slide 5

Wake Shedding Frequency vs Re from Single Cylinder

Simulated Re in current study

Slide 6

Flow Interference Flow Characteristics (Cylinders in Tandem)

• Flow interference imposes

continuous and discontinuous changes in vortex shedding

• Cylinder oscillations modified

by and strongly dependent

• n cylinder arrangement

Slide 7

Wake Shedding States (Cylinders in Tandem)

• Critical tandem cylinder spacing

configuration of L/D = 3.7 chosen

• Bistable

flow state exists between cylinders

• 1.50
• 1.00
• 0.50

0.00 0.50 1.00 1.50

0.02 0.07 0.12 0.17

• 0.20
• 0.15
• 0.10
• 0.05

0.00 0.05 0.10 0.15 0.20

CL_Downstream Time t/s CL_Upstream Upstream & Downstream Cylinder CL vs Time (DES)

CL_Upstream CL_Downstream

Intermittent shedding state Constant shedding state

Slide 8

CFD Simulations of Cylinder Flow at Re = 3900 (URANS, LES & DES)

Slide 9

Meshing and Testing Conditions

Microphone Positions

• Trimmer mesh of 3 million cells
• URANS,LES,DES
• Diameter of 20mm and span of

80mm (4D)

• Periodic boundary conditions at

cylinder ends

• Time –Step: 1.0e-5 sec
• Reynolds Number studied: 3900
• Aeroacoustics module:
• Ffowcs Williams – Hawkings

X Y Z

Slide 10

Comparison of Time Averaged Results (Re=3900)

Cases Span Cd Strouhal no. Experimental 4D 1.01 0.205 URANS 4D 1.078 0.214 LES 4D 0.998 0.213 DES 4D 1.088 0.196

• 1.5
• 1.4
• 1.3
• 1.2
• 1.1
• 1
• 0.9
• 0.8
• 0.7
• 0.6
• 0.5
• 0.4
• 0.3
• 0.2
• 0.1

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

• 1.2
• 1.1
• 1.0
• 0.9
• 0.8
• 0.7
• 0.6
• 0.5
• 0.4
• 0.3
• 0.2
• 0.1

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5

60 160 260

CL Cd Time t (U/D)

Cd and CL vs Time (DES simulation)

Far Field Frequency of 333 Hz

• > Strouhal no. ~0.196

Slide 11

Streamwise Reynolds Stresses

0.0000 0.0250 0.0500 0.0750 0.1000 0.1250 0.1500 0.1750 0.2000 0.2250

• 3.0
• 2.0
• 1.0

0.0 1.0 2.0 3.0

<u’u’

z/d <u'u'> vs z/d at x/d=1.54 plane

Experiment DES URANS LES

Streamwise Reynolds Stress DES URANS LES

• DES predicts

comparable peak values as compared to exp results

• Higher level of mixing

predicted at the wake centre

• LES under predicts

peak values as compared to exp results

• URANS under predicts

<u'u'> in the wake

Slide 12

Shear & Spanwise Reynolds Stress

• 0.2000
• 0.1500
• 0.1000
• 0.0500

0.0000 0.0500 0.1000 0.1500 0.2000

• 2.0
• 1.0

0.0 1.0 2.0

<u’v'> z/d <u’v'> vs z/d at x/d=1.54 plane

Experiment URANS LES DES

• 0.0010

0.0090 0.0190 0.0290 0.0390 0.0490 0.0590 0.0690 0.0790 0.0890 0.0990

• 3.0
• 2.0
• 1.0

0.0 1.0 2.0 3.0

<w’w'> z/d <w‘w'> vs z/d at x/d=1.54 plane

Experiment URANS LES DES

Slide 13

Flow Structures Visualized by the Q Criteria (DES simulation, Re=3900)

• Pairs of counter-

rotating streamwise vortices -> Karman vortex shedding characteristics

• Longitudinal vortices

interlaced between counter-rotating vortices

Slide 14

OSPL Comparison at 70 Diameter

Cases Overall Sound Pressure Level (OSPL) Peak Frequency Peak Strouhal no.

WT data (Journal of Sound and Vibration)

83.8 308 0.193

DES

83.6 313 0.196

70D Receiver position D

Slide 15

Far-Field Sound Directivity Pattern

• Microphones are placed at 70D around the

cylinder monitoring total pressure

• Compute the ΔP’rms (pressure fluctuation

component) at r=70D, non-dimensionalised by free stream velocity and density

0.00002 0.00004 0.00006 0.00008 0.0001

90 75 60 45 30 15 345 330 315 300 285 270 255 240 225 210 195 180 165 150 135 120 115

ΔP'rms vs Receiver Positions

• Far field directivity

pattern exemplify the characteristics of dipole sound propagation

Slide 16

CFD Simulations of Cylinder Flow at Re = 46,000 (DES)

Slide 17

Meshing and Testing Conditions

Microphone Positions

• Trimmer mesh of 3.6 million

cells

• DES
• Diameter of 9.8mm and span
• f 29.4mm (3D)
• Periodic boundary conditions

at cylinder ends

• Time –Step: 1.0e-5 sec
• Reynolds Number studied:

46000

• Aeroacoustics module:
• Ffowcs Williams –

Hawkings

X Y Z

Slide 18

Time Averaged Results for Re = 46000

Cases CD,average CD,rms Strouhal no.

Experimental

1.35 0.16 0.19

LES_OpenLit

1.24 0.10 0.19

DES_current

1.235 0.141 0.20

CL

• 1.50
• 1.30
• 1.10
• 0.90
• 0.70
• 0.50
• 0.30
• 0.10

0.10 0.30 0.50 0.70 0.90 1.10 1.30 1.50 1.70 1.90 300 350 400 450 500 550

Time t(U/D)

CD

CD,average CL,average

Far Field Frequency of 1455.8 Hz - > Strouhal no. ~0.20 CL

Slide 19

Reynolds Stresses Characteristics at x/d=1.54 (Re=46,000)

0.000 0.010 0.020 0.030 0.040 0.050 0.060

• 3
• 2
• 1

1 2 3

<w’w'> z/d <w’w'> vs z/d

0.000 0.100 0.200 0.300 0.400 0.500 0.600

• 3
• 2
• 1

1 2 3

<v’v'> z/d <v’v'> vs z/d

• 0.150
• 0.100
• 0.050

0.000 0.050 0.100 0.150

• 3
• 2
• 1

1 2 3

<u’v'> z/d <u’v'> vs z/d

0.000 0.050 0.100 0.150 0.200

• 3
• 2
• 1

1 2 3

<u'u'> z/d <u'u'> vs z/d

• Trends of the

Reynolds stresses are typical to that of a turbulent wake

Slide 20

Flow Structures Visualized by the Q Criteria (DES simulation, Re=46,000)

Slide 21

20 40 60 80 100

90 60 30 330 300 270 240 210 180 150 120

SPL vs Receiver Positions

DES Experiment

Sound Directivity Pattern in terms of Prms & OSPL

• SPL of Experiment 91dB
• SPL of DES~92dB

Occurring at 1455.8Hz which corresponds to St number of 0.20

• SPL at other positions

match quite closely between experimental and CFD results

0.00E+00 2.00E-05 4.00E-05 6.00E-05 8.00E-05 1.00E-04 1.20E-04 1.40E-04

90 75 60 45 30 15 345 330 315 300 285 270 255 240 225 210 195 180 165 150 135 120 115

ΔP'rms vs Receiver Positions

Slide 22

CFD Simulations of Tandem Cylinder Flow at Re = 1.66E5 (DES)

Slide 23

Meshing and Testing Conditions

Microphone Positions

• Trimmer mesh of 6.2 million cells
• DES (K-w sst)
• Diameter of 57.15mm and span of

171.45mm (3D)

• Periodic boundary conditions at

cylinder ends

• Time –Step: 2.0e-5 sec
• Physical Time Simulated: 0.216 sec
• Reynolds Number studied: 1.66E5
• Aeroacoustics module:
• Ffowcs Williams – Hawkings

X Y Z

Slide 24

20 40 60 80 100 120 140 10 100 1000 PSD (dB/Hz) Frequency DES DES_Far field DES_Near field

Comparison of Time Averaged Results

Upstream 90 Deg Experiment CFD(Literature) DES_Near field DES_Far field Span 18D 18D 3D 3D Frequency 178Hz 166Hz 158Hz 166Hz Strouhal no. 0.232 0.219 0.203 0.213 Near field Frequency of 158 Hz

• > Strouhal no. ~0.203

Far field Frequency of 166 Hz -> Strouhal no. ~0.213

Slide 25

Flow Structures Visualized by the Q Criteria (DES simulation, Re=1.66E5)

• Wake interference

amplifies downstream shedding and

• scillation
• Wake interference

damp out downstream shedding and

• scillation
• Counter-rotating

streamwise vortices

• bserved in inter-

cylinder flow region

• Constant shedding

flow state upstream

• Only shear layer

roll up is observed in inter-cylinder flow region

• Intermittent

shedding state upstream

Slide 26

Near Field Pressure Spectra

70 80 90 100 110 120 130 10 100 1000 PSD (dB/Hz) Frequency Upstream Cylinder 90 deg Spectra DES Literature_CFD Literature_Experimental 70 80 90 100 110 120 130 140 10 100 1000 PSD (dB/Hz) Frequency Downstream Cylinder 90 deg Spectra DES Literature_CFD Literature_Experimental

• Shedding frequency of near field spectra in good agreement with literature CFD results.
• Deviation in peak values could be attributed to insufficient simulation time, where the bi-

stable flow behaviour have yet to be statistically converged.

Slide 27

Microphone Spectra at 30D

Receiver / Microphone position

25 35 45 55 65 75 85 95 20 200 2000 PSD (dB/Hz) Frequency Microphone A DES Literature_CFD Literature_Experiment 25 35 45 55 65 75 85 95 20 200 2000 PSD (dB/Hz) Frequency Microphone B DES Literature_CFD Literature_Experiment 25 35 45 55 65 75 85 95 20 200 2000 PSD (dB/Hz) Frequency Microphone C DES Literature_CFD Literature_Experiment

A B C ~30D

Peak SPL (dB)= 92.5 (exp 93.7) Peak SPL (dB)= 91.6 (exp 95.6) Peak SPL (dB)= 88.5 (exp 92.7)

Slide 28

Summary

• Flow over cylinder at Re 3900 using URANS, DES and LES

– Strouhal number at vertical height of 70D away from the cylinder= 0.196 (exp 0.193); OSPL = 83.6 dB (exp83.8 dB) – Directivity pattern of Δp’rms of receivers around the cylinder exemplify dipole sound propagation characteristics – Trends of DES predicted Reynolds stresses were in relative good agreement with experimental results – URANS & LES had tendency to under predict the magnitude of the principal components of the Reynolds stresses

• Flow over cylinder at Re 46,000 using DES

– Fundamental Strouhal number = 0.2 (exp 0.19) at frequency of 1455.8 Hz – SPL at vertical height of 70D away from = 92 dB (exp 91dB) – Directivity pattern of Δp’rms of receivers around the cylinder exemplify dipole sound propagation characteristics – Trends of the Reynolds stresses are typical to that of a turbulent wake

Slide 29

Summary

• Flow over tandem cylinder at Re 1.66E5 DES

– Bi-stable flow states at critical cylinder spacing captured – Flow between cylinder switches between constant shedding and intermittent shedding modes – Near field strouhal number at cylinder surface = 0.203 and far field = 0.213(exp 0.232) – Trends of DES predicted surface pressure distribution were in relative good agreement with experimental results – Good farfield OASPL agreement with experiment at respective microphone

• locations. Microphone A = 92.5 (exp 93.7) Microphone B = 91.6 (exp 95.6)

Microphone C = 88.5 (exp 92.7) – Directivity pattern of Δp’rms of receivers around the cylinder exemplify dipole sound propagation characteristics