2009, TSI Incorporated Stereoscopic Particle Image
Velocimetry
Slide 2
2009, TSI Incorporated Stereoscopic PIV Need for Stereoscopic
Measurements Most flows are three-dimensional in nature Need
simultaneous measurement of the three orthogonal components 2D flow
measurements using a Single camera Edges of the images are viewed
obliquely Out-of-plane motion appears to be in-plane motion Errors
due to these need to be corrected Stereoscopic measurement
eliminates these errors
Slide 3
2009, TSI Incorporated Stereoscopic Technique View the light
sheet from two perspectives Two cameras set up at different angles
to illuminated plane Each camera captures a pair of images 2D image
displacements for each camera image field 3D displacement obtained
from the two 2D displacements Calibration or Mapping function
generation imaging point markers in the flow using both cameras
calibration grid with equally spaced markers used Effect of window
refraction and distortion accounted for Mapping function generates
a one-to-one correspondence between marker positions and their
image locations in the camera
Slide 4
2009, TSI Incorporated Particle Image Velocimetry 3 Component
measurements Three Component PIV Measurements Measurement of 3
components of velocity simultaneously Illumination : using a light
sheet 3 components of measurements in a plane
Slide 5
2009, TSI Incorporated System Components PIV laser and light
sheet optics Two P OWER V IEW ( or PIVCAM ) cameras, lenses
Mounting fixture for the Scheimpflg configuration Two high speed
camera interfaces Stereoscopic camera alignment mount Dual-plane
Dual-sided (DPDS) target plate LaserPulse Synchronizer Stereoscopic
I NSIGHT software package Tecplot includes Tecplot package
Slide 6
2009, TSI Incorporated Scheimpflg Stereoscopic Arrangements
back-scatter forward-scatter side-scatter Measurement plane
parallel to the bisector of the camera axes
Slide 7
2009, TSI Incorporated Plane of Focus Out of Focus: behind
plane of focus Out of Focus: in front of plane of focus Point of
Focus CCD Array Camera Lens Only Particles in the light sheet can
be captured by the camera The plane of focus is parallel to the
sensing array Portions of light sheet in front of and behind the
plane of focus are out of focus Scheimpflg Stereoscopic
Arrangement
Slide 8
2009, TSI Incorporated Scheimpflg Stereoscopic Arrangement
Object plane (Light sheet) Lens principal plane Scheimpflg
Condition Plane of Focus Axis of Sensing Array Axis of Lens By
rotating the sensing array with respect to the lens plane most of
the objective plane can be focused
Slide 9
2009, TSI Incorporated Scheimpflg Stereoscopic Arrangement
Object plane (Light sheet) Combine for a 3D Vector Left Camera
ViewRight Camera View
Slide 10
2009, TSI Incorporated Velocity vector in the light sheet Z x f
= (x + x, y + y, z + z ) Image plane XiXi XfXf d1d1 d0d0 XX Y -
axis normal to the plane of the paper B x i = (x, y, z) A xx Laser
light sheet
Slide 11
2009, TSI Incorporated 3-D Displacements in the flow X left = x
fluid (dX left /dx fluid )+ y fluid (dX left /dy fluid )+ z fluid
(dX left /dz fluid ) Y left = x fluid (dY left /dx fluid )+ y fluid
(dY left /dy fluid )+ z fluid (dY left /dz fluid ) X right = x
fluid (dX right /dx fluid ) + y fluid (dX right /dy fluid )+ z
fluid (dX right /dz fluid ) Y right = x fluid (dY right /dx fluid )
+ y fluid (dY right /dy fluid )+ z fluid (dY right /dz fluid ) X, Y
are the measured image displacements - x left corresponds to the
image displacement in the left camera x, y and z are the particle
displacements in the flow
Slide 12
2009, TSI Incorporated Perspective effect due to camera tilt A
A B B B B A A A A B B Regular grid in fluid Left camera image of
grid Right camera image of grid
Slide 13
2009, TSI Incorporated Stereoscopic technique - Calibration
Image recording plane Camera 1 Image recording plane Camera 2
Calibration target Refracting wall Registration of the two cameras
- align to view the same region Distortion correction due to
different media Generates mapping function to map the vectors in
the camera plane back to the object plane
Slide 14
2009, TSI Incorporated Mapping function generation Calibration
Use rectangular grid of dots as calibration plate Plate with grid
markings Dual-Plane Dual-Sided (DPDS)Target Introduced by TSI No
need to traverse Plate with grid markings in multiple planes on
both sides of the plate Calibration grid defines the coordinate
system Align the calibration plate with the light sheet DPDS
Target
Slide 15
2009, TSI Incorporated Calibration Target Dual-plane target
Image of the target from the left camera Image of the target from
the right camera
Slide 16
2009, TSI Incorporated Display and Post Processing INSIGHT
Stereo & TecPlot
Slide 17
2009, TSI Incorporated Remote control for PIV systems Remote
Scheimpflug control Remote focusing Remote aperture control Used
for Underwater applications, Large tunnels Facilities where remote
access is needed
Slide 18
2009, TSI Incorporated Guidelines for good Results
Interrogation spot size small enough so that one vector correctly
describes the flow within that region velocity gradient within the
region is negligible Three or more particle pairs per interrogation
spot improvement in accuracy is small for cases for more than 5
pairs of images Max. in-plane displacement < 1/4 of
interrogation spot size Min. in-plane displacement could be zero
Maximum out of plane displacement Less than of light sheet
thickness