Particle Image Velocimetry (PIV) is a laser-based technique used to measure instantaneous velocity fields in fluids. It works by illuminating seed particles in the flow with a laser sheet, recording images of the particles with a camera, and using image processing to determine the displacement of particles between images from which velocity fields can be derived. The document discusses the history and principles of PIV, components of a PIV experimental setup including lasers, cameras, seeding particles, and post-processing techniques to analyze PIV data and identify spurious vectors. Applications of PIV include a wide range of industrial and academic fluid flow problems.

1. PARTICLE IMAGE
VELOCIMETRY
Subject : Fluid Mechanics
Semester : IV semester
Supervisor : Dr. V. K. Patel
Presenter : Raj Zunke
Hemant Rawat
Amar Prem

2. What we are going to discuss ?
• What is PIV AND its brief history
• Principle of working
• Construction of experimental setup
• Components and their description
• Post processing of data
• Other PIV techniques
• Advantages and Disadvantages
• Application

3. It is a double-pulsed laser technique used to measure
instantaneous velocity distribution in a plane of flow
by determining the displacement of particles in that
plane during a short time interval.
HISTORICAL ASPECTS
• Origins: Flow visualizations
• 1970’s: Laser Speckle Velocimetry
• 1980’s: LSV,PTV, PIV,
• Further development of LASER , CCD cameras , Computers lead to the
development of PIV
• Computers First scientific paper on PIV was published in 1984
• First commercial PIV systems came in 1988 .

4. Experimental setup of the PIV

5. Physical representation of PIV

6. • The PIV technique for velocity measurement is based on flow
visualization and image processing .
• The first step is to trace the flow with suitable seed particles in order
to obtain the path lines of fluid motion.
• A pulse of laser light illuminates certain region of flow field at any
desired plane and the photographic view is recorded digitally by
using a video camera positioned at right angle to the plane.
• After a short interval of time , the particles are illuminated again
through the laser light and the new positions are recorded.
• Using the information of both the images, the particle displacement
is determined and subsequently the magnitude of velocity of the
particle in the plane is calculated.

7. • Acceleration of particle = Viscous resistance +Acceleration
due to Pressure gradient + Resistance of inviscid fluid
due to acceleration of sphere + Resistance due to
flow field unsteadiness
• Body force and centrifugal force (swirling flow) can also
be other important forces
• Response of the velocity field to different velocity
Fluctuations provides the criteria on ideal particle tracking
.

8. COMPONENTS
SEEDING PARTICLES-
 These are an inherently critical component of the PIV system.
Depending on the fluid under investigation, the particles must be
able to match the fluid properties reasonably well. Otherwise they
will not follow the flow satisfactorily enough for the PIV analysis to
be considered accurate.
 Refractive index for the seeding particles should be different from
the fluid which they are seeding.
 The particles are typically of a diameter in the order of 10 to 100
micrometres.
 Silicon carbide, titanium dioxide and polystyrene latex particles are
few categories of seed particles that are used depending on the type
of fluid (liquid/gas).

9. CAMERA
To perform PIV analysis on the flow, two exposures
of laser light are required upon the camera from the
flow.
 Originally, with the inability of cameras to capture
multiple frames at high speeds, both exposures were
captured on the same frame and this single frame
was used to determine the flow.

10. LASER AND OPTICS
 For macro PIV setups, lasers are predominant due
to their ability to produce high-power light beams
with short pulse durations.
 The optics consist of a spherical lens and
cylindrical lens combination. The cylindrical lens
expands the laser into a plane while the spherical
lens compresses the plane into a thin sheet.
 The correct lens for the camera should also be
selected to properly focus on and visualize the
particles within the investigation area.
 Laser Light: Almost constant thickness and without
any aberration
 Continuous Laser: He - Neon, Argon Laser

11. SYNCHRONIZER
The synchronizer acts as an external trigger
for both the cameras and the laser.
 Controlled by a computer, the synchronizer can
dictate the timing of each frame of the CCD
camera's sequence in conjunction with the firing
of the laser to within 1 ns precision.

12. POST PROCESSING
Spurious vectors !!!!!
• -Low particles density
• -Inhomogeneous particles seeding
• -Particles within a vortex
• -Low S/N
• - 3D movement of the particles
Why the spurious vectors have
to be eliminated ?
Induce errors in velocity derivatives. Spurious vector

13. Other PIV techniques
Micro PIV
Particles size: from nanometers to several
microns.
• The particles should be large enough
to dampen the effects of Brownian
motion:
• Brownian motion results from the
interaction between the particles.
This prevents the particles to follow
the flow.
The relative error in the measured
particle displacement is:
t
D
u 

21


14. Advantages of PIV
1-Entire velocity field can be calculated.
2-Capability of measuring flows in 3-D space
3-Generally, the equipment is nonintrusive to flow
4-High degree of accuracy
Disadvantages of PIV
1-Requires proper selection of particles
2-Size of flow structures are limited by resolution of image
3-Costly

15. Applications
PIV has been applied to a wide range of flow problems,
varying from the flow over an aircraft wing in a wind
tunnel to vortex formation in prosthetic heart valves. 3-
Dimensional techniques have been sought to analyse
turbulent flow and jets.
Rudimentary PIV algorithms based on cross-correlation
can be implemented in a matter of hours, while more
sophisticated algorithms may require a significant
investment of time. Several open source
implementations are available. Application of PIV in the
US education system has been limited due to high price
and safety concerns of industrial research grade PIV
systems.