Scanning Multiple Projection

Digital Image

Processor

Stroboscope

Through 2D Recording

Through 3D Recording

Paths to 3D PIV

Holography

Principle of HPIV

DisplacementVelocity

Holocine (time resolved)

t1 t2 t3

Hologram

8ns

LaserPulse

3D flow seeded with particles

Recording

CCD

Interrogationcamera

Laser Beam

Reconstruction

Double Exposure

t1 t1+ t t2 t2+ t

Advantage of holography

True 3D imaging Instantaneous Volumetric High Information Capacity

(106 - 109 Particles)Real-Time Recording but Off-line Data Transfer

& Processing

How to get true 3D imaging?

Phase Preservation

O=Oexp[i(-t)] or: O=Osin(t)

How to record ?

Any light sensitive media records intensity I=|O|2 =O2

Need to “encode” phase into some intensity modulation

Encoding Phase

-- Use interference of coherent light!

E = R + O

Reference wave Object wave

where R = R exp[i(-t)] , O=Oexp[i(-t)]

Recorded Intensity:

I=|R+O|2 = R2 + O2 +2ROsin()

Real Image

Principle of Holography

Reference Beam

Virtual Image

x

z

Hologram

0

RecordingReference Beam

Reconstruction

y

x

z

Hologram

0

ObjectI =|R+O|2 = R2 + O2 +2ROsin()

R

O

O

I =(R+O)(R+O)* = R2 + O2 + R*O+RO*

O*T ~ R2 + O2 + R*O+RO*

Usually R= exp(-it) T ~ 1 + O2 + O + O*

Experimental Demonstration

Reference beam, object beamVirtual, real image*Transmission or Reflection Hologram?

Setup Considerations:

Coherence length vs. path length difference

Exposure energy: In the linear range

R:O ratio

Transmission or Reflection Hologram

Transmission hologram created by 2 plane waves traveling towards the same side

Reflection hologram created by 2 plane waves traveling towards opposite sides

(Volume Hologram)

Reflection Hologram

Bragg Condition2dsin=m

In-line (Gabor) Holography

Simple geometry Low coherence &

energy requirement

Traditional for particle fields

Speckle noise

(limit seeding density & seeding depth)

Large depth of focus

(practically only 2D vectors)

Reference wave

Object wave

LASER

LASER

Real ImageViral Image

Speckle Noise (in-line hologram)

Reconstruction field of an in-line hologram for an ensemble of particles: B + ok+ o*k

Type-I speckle -- interference between B and the scattered waves Major Source of SpeckleType-II speckle -- self-interference of the scattered waves.

Ok = ok= kexp(ik) : Random Walk

Speckle noise: decrease Signal-to-Noise Ratio

1 particle /mm3 6 particles /mm3 40 particles /mm3

Off-Axis Holography as Solution

Off-axis HPIV:Higher SNRHigher Seeding Density

Complex GeometryHigher Coherence Required

Reconstruction

VirtualImage

RealImage

Hologram

ReferenceBeam

Hologram

IlluminatingBeam

ReferenceBeam

Recording

Off-axis HPIV

Reconstruction

VirtualImage

RealImage

Hologram Hologram

ReferenceBeam

ReferenceBeam

In-line HPIV

Recording

In-Line HPIV:Simple GeometryLower Coherence Required

Intrinsic Speckle NoiseLower Seeding Density

IROV In-line Recording Off-axis Viewing Holography

IROV: Use side scattering Suppresses speckle noise Reduces image depth of focus

Making In-line based HPIV feasible

Ho lo g ra mVirtua lIm a g e

Ho lo g ra mRe a lIm a g e

Re c o rd ing Re c o nstruc tio n

Re fe re nc eBe a m

Re fe re nc eBe a m

C o nve ntio na lIn-line

IRO V

Meng & Hussain (1995): Appl. Opt. 34, 1827

Recording Reconstruction

IROV Experimental SetupIROV Experimental Setup

Use of High-Frequency Fringes on In-Line Holograms

Negligible influence of forward scattering: Since |OL| << |R|, IL << I sig

IROV suppresses speckle noise

•Completely avoids type-I speckle

•greatly reduces type-II speckle

Reconstruction field of an in-line hologram for an ensemble of particles: B + ok+ o*k

Off-axis Viewing: receives only o*k

Improved SNR by IROV

IROV

In-line Viewed

Reduction of Depth of Focus by IROV

0 degree 20 degree

In focus

+100 m

-100 m

In-line: Fraunhofer diffraction

Proof of Principle Experiment

IROV Measurement of a Vortex Ring

Post Processing

Low density requires intelligent pairing

GA searches large solution space

IROV Data Processing: Genetic Algorithm Particle Pairing

2’

1’

3’

4’

5’

6’

7’1

2

34

5

67

Interrogation Cell 3

12

,,, RzyxPtt

PPV i

iiii

Genetic Algorithm Particle Pairing

Why Genetic Algorithm?

Many possibilities to pair particles Need to numerate and filter

Conventional searching methods

Computation intensive Difficult to incorporate

intelligence Time consuming

Genetic Algorithm Efficient in searching large space Built-in intelligence to follow fluid

dynamics Fast and inherent parallel processing

speed

Large solution space

Two Approaches of HPIVDeveloped at LFD

Off-axis HPIVhigh-end

In-line (IROV) HPIVlow-cost

Digital In-line Holography

Dual-Reference Off-Axis TechniqueDual-Reference Off-Axis Technique

High Seeding Density AllowedSmall Depth of FocusImage Separation Removes Direction Ambiguity

Complex Optical GeometryHigh Energy Laser RequiredHigh Coherence of Beam Needed

Beam Expander

Be

am

Ex

pa

nd

er

B eam Expander

Beam Handling U nit

Variable B eam Splitter

Referenc e 1

Referenc e 2

M irror

M irror

Dumper

H EM

H EM

H EM

H EM H EM H EM H EM

H EM

H EMP

BS

PB

S

B SBS

WP WP

Sh

utt

er

1

Sh

utt

er

2

Pa

rtic

leF

ield

(Vo

rte

x)

I l luminating B eam

H olographic Exposure U nit

Sy

nc

hro

niz

er

Digita lDelayGenerator

Ho

log

ram

Dual Seeded YAGL aser (P IV-400)

Beam Expander

Beam Expander

Beam Handling U nit

Variable B eam Splitter

Referenc e 1

Referenc e 2

M irror

M irror

H EM

H EM

H EM H EM H EM H EM

H EM

H EM

PB

S

PB

S

B SBS

WP WP

Sh

utt

er

1

Sh

utt

er

2

Rec onstruc tedPar tic leImage

I lluminating B eam

H olographic Rec onstruc tionU nit

Dumper

Digita lCamera

3D Travers eSystem

200M HzPentium P roP roc ess or

64M BM emory

Digita l ImageFramegrabber

H ardDis k

P C I Bus

M otionContro ller

M otorDriver

Dual Seeded YAGL aser (P IV-400)

Gemini Off-axis HPIV System

Concise Cross Correlation(CCC) Algorithm

Matching by particle groups Uses particle centroids only Group shifting for matching Decomposition of operation Low data volume / high

compression rate High-speed processing

System Test FlowExcited Air Jet

P ow erA mplifi er

P L LFrequenc yM ult iplier

VaiableDelayer

WaveformShaper

Vor tex Sync hronizer

Droplet-s eededInjec tion A ir F low

Digital DelayGenerator

Beam E xpander

Objec tBeam

Speaker/E xc iter

Vor tex

Dual SeededYA G L as er(P IV-400)

Phase-Locked Vortex

Side View Top View

Vorticity

Vorticity Iso-surface

To be re-made

HPIV Measurement of Tab Wake

Vortab Flow: HPIV Measurement Result

Amount of Data: 400,000 Vectors

Mean Velocity: 16.67 cm/sec.

Vortab Flow: Vorticity Iso-Surfaces

Hologram captures 3D instantly

TurbulentFlow Field

HPIV = 3D InformationTransfer & Processing

Fundamental Challenges

3D Signal DecodingComplex Flow MappingLarge Data QuantityUser-friendly?

Flow Field Reconstruction

Holographic Flow Visualization

a Tool for Studying 3D Coherent Structures and Instabilities

Kansas State University, ISSI,Wright Laboratory, WP/AFB

d

(a) (b) (c)

Holographic Images of Three Vortex-Flame Systems Photographed from Two Angles (a) or Using Two Magnifications (b and c).

Off-Axis HFV of Vortex Flame

b ca

Holographic Images of A Milk Drop Undergoing Bag Instability (a, b)

Holographic Images of A Turbulent Milk Drop (a) and Its Downstream Breakdown (b, c)

IROV HFV of Turbulent Milk Drop

Naturally, HPIV is an ideal diagnostic tool for studying particulate phase

3D and dynamically