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Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL. Instructor: Lichuan Gui [email protected] http:// lcgui.net. Lecture 20. Particle image displacement methods and others.

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Instructor lichuan gui lichuan gui@uiowa edu http lcgui net

Measurements in Fluid Mechanics058:180:001 (ME:5180:0001)Time & Location: 2:30P - 3:20P MWF 218 MLHOffice Hours: 4:00P – 5:00P MWF 223B-5 HL

Instructor: Lichuan Gui

[email protected]

http://lcgui.net


Instructor lichuan gui lichuan gui uiowa lcgui

Lecture 20. Particle image displacement methods and others


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

- Optical, non- or minimally-intrusive, fluid flow measurement technique;

- Instantaneous flow measurements in two-dimensional (2D) area or three-dimensional (3D) volume field of views;

- Basic procedure of particle image displacement methods

1. Flow visualization

- Flow field seeded with small tracer particles

- Particles usually illuminated by a laser light sheet

2. Image recording

- Particle images captured by an imaging system

- Saved in photographic film or digital image file

3. Image evaluation

- Young’s fringes method

- Particle image identification

- Correlation-based algorithm


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

Example:


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

Three groups of methods

Particle tracking velocimetry (PTV)

- flow seeded with tracer particles of very low concentration

- very low image number density in photo or video recordings

- single particle can be identified in image recording

- particle image tracking possible from frame to frame

- low information density in measurement plane

Laser speckle velocimetry (LSV)

- flow seeded with tracer particles of very high concentration

- very high image number density in photo or video recordings

- single particle can not be identified in image recording

- particle image tracking impossible from frame to frame

- high information density in measurement plane

Particle image velocimetry (PIV)

- flow seeded with tracer particles of high concentration

- high image number density in photo or video recordings

- single particle can be identified in image recording

- particle image tracking impossible from frame to frame

- high information density in measurement plane


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

Single frame image recordings

Single exposure- Long exposure time- Velocity determined by trajectory- Direction ambiguity - Low particle number density required

Double exposure- Short exposure time- Velocity determined by displacement - Direction ambiguity- Methods to avoid direction ambiguity: a. color/intensity tagging b. Image shifting techniques

Multi-exposure- Short exposure time- Velocity determined by displacement- Direction ambiguity- Used to increase particle image number- Limited in steady flow


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

Multi frame image recordings

- velocity determined with particle image displacement between frames

- double/Multi exposure used to increase image number in steady flow


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

Frequently used evaluation methods

HID – high image density (PIV)

LS – laser speckle mode (LSV)

LID – low image density (PTV)


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

Image plane

Laser light sheet

Objective Lens

S’

Image plane

Objective Lens

Laser light sheet

L’

L

S

Data reduction

Scale factor:  = L/L’

Time interval: t

Velocity:V=S/t=·S’/ t


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

y

x

Evaluation methods

Particle trajectory identification

Image recording

- single frame

- single long time exposure

- low image density

- film or digital recording

Evaluation

- read film recordings with

a microscope system

- identify particle trajectories

in digital recording


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

laser

PC

2D traversesystem

frosted glass

CCD camera

Evaluation methods

Young’s fringes method

Image recording

- positive film

- single frame

- double/multiple exposed

- HID & LS mode

Young’s fringes system

- SM inversely proportional to SA

- fringes perpendicular to particle image displacement


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

(x2, y2)

(x1, y1)

Evaluation methods

Particle image tracking

PIV recording- Minimum 2 frames- Single exposure - LID mode- Film or digital recording

Evaluation- Identify particle images & determine position of each particle image center- Pairing particles in two frames (many algorithms)- Velocity determined by position difference of paired particles & t

y

y

t1

t2

o

x

o

x


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

(m, n)

-S

S

n

o

m

(m’,n’)

Cross-correlation

Auto-

correlation

Evaluation methods

Correlation-based interrogation


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

Light

sheet

Image #1

t=t0

Exposure #1

Single exposed recording

Double exposed recording

Standard 2D PIV

t=t0

Lens

Measurement

volume

Laser

Fluid flow seeded with

small tracer particles

Lens system & Camera


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

Light

sheet

Image #2

t=t0+t

Exposure #2

Standard 2D PIV

t=t0+t

Lens

Measurement

volume

Laser

Image #1

t=t0

Fluid flow seeded with

small tracer particles

Exposure #1

Lens system & Camera

Single exposed recording

Double exposed recording


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

MCROFLUIDIC DEVICE

Micro Device

Flow out

Flow in

CCD CAMERA

Glass

cover

MICROSCOPE

Focal Plane

Flood Illumination

BEAM EXPANDER

Microscope

Beam

Expander

Nd:YAG LASER

Epi-fluorescent

Prism / Filter Cube

Nd:YAG Laser

l=532 nm

Micro-PIV image pair

l = 610 nm

CCD Camera

(1280x1024 pixels)

Micro-scale PIV (MPIV)

Micro-Fluidics LabPurdue University


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

Stereo PIV (SPIV)

  • - 3 velocity components in a plane

  • - Two cameras

  • - Translation systems (lateral displacement)

  • - Rotational systems (angular displacement)Scheimpflug condition


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

Holographic PIV (HPIV)

- 3 velocity components in a 3 dimensional volume

- Complex and precise illumination

  • a. Hologram recording

  • b. Hologram reconstruction


Instructor lichuan gui lichuan gui uiowa lcgui

Particle image displacement methods

Other image-based methods

  • Defocusing PIV (Pereira et al. 2000)

    • Allow images to become defocused

    • Single camera/ color CCD, particle image tracking

  • Multiple-sheet PIV (Raffel et al.,1995 )

    • Multiple laser light sheet, single camera

  • 3D scanning PIV (Brücker, 1997)

    • Scanning a 3D volume with a laser beam

    • Single high speed camera

  • X-ray & Echo PIV

  • Molecular Tagging Velocimetry

  • Temperature measurement with particle Brownian motion

  • More


Instructor lichuan gui lichuan gui uiowa lcgui

Measurement of wind velocity

Cup anemometers

Propeller anemometers

Vane anemometers

Sonic anemometers


Instructor lichuan gui lichuan gui uiowa lcgui

Homework

- Read textbook 11.4-11.5 on page 275 - 284

  • Questions and Problems: 9 on page 287

- Due on 10/12


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