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Instructor: Lichuan Gui lichuan-gui@uiowa lcgui

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 lichuan-gui@uiowa.edu http:// lcgui.net. Lecture 20. Particle image displacement methods and others.

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Instructor: Lichuan Gui lichuan-gui@uiowa lcgui

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  1. 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 lichuan-gui@uiowa.edu http://lcgui.net

  2. Lecture 20. Particle image displacement methods and others

  3. 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

  4. Particle image displacement methods Example:

  5. 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

  6. 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

  7. 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

  8. Particle image displacement methods Frequently used evaluation methods HID – high image density (PIV) LS – laser speckle mode (LSV) LID – low image density (PTV)

  9. 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

  10. 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

  11. 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

  12. 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

  13. Particle image displacement methods (m, n) -S S n o m (m’,n’) Cross-correlation Auto- correlation Evaluation methods Correlation-based interrogation

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. Measurement of wind velocity Cup anemometers Propeller anemometers Vane anemometers Sonic anemometers

  21. 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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