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3D-PTV is a 3D Particle Tracking Velocimetry experimental technique used in the experimental research of turbulence. main source of information is http://ptvwiki.netcipia.net
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3D-Particle Tracking Velocimetry
an overview
by
Beat Lüthi
Some applied flows one would like to know more about
from Matthias Machacek (2003) PhD Thesis ETH
applied flow in wind tunnel: car
from Matthias Machacek (2003) PhD Thesis ETH
more abstract but still applied flow: delta wing
Some applied flows one would like to know more about
Some applied flows one would like to know more about
G. Wilkesanders, Ch. Skallerud, Univ. of Colorado at Boulder Visualized in rheoscopic fluid made of fish scales in water.
The wake of a bluff body generated a von Karman vortex street
Main idea of 3D-PTV
How to measure a flow field?How to get 3D information?How to get Lagrangian information?How to not disturb the flow?
3D-PTV
Main idea of 3D-PTV
3D-PTV =
image basedthree dimensional Lagrangianflow measurement technique
(Particle Tracking Velocimetry)
flow + CCD cameras + computers = 3D-PTV
Main idea of 3D-PTV
from Matthias Machacek (2003) PhD Thesis ETH
smoke streaks yield ’only’ quantitative information
Main idea of 3D-PTV
from Matthias Machacek (2003) PhD Thesis ETH
3D-PTV yields quantitative, Lagrangian flow trajectories
Main idea of 3D-PTV
from Matthias Machacek (2003) PhD Thesis ETH
… zooming in more: flow details behind delta wing
Main idea of 3D-PTV
from Heinrich Stüer (1999) PhD Thesis ETH
more ’fundamental’ flow: backward facing step
Main idea of 3D-PTV
from Berg (2006) PhD Thesis Risø
’fully fundamental’: isotropic turbulence
Main idea of 3D-PTV
to follow a 3D (!) particle positionas opposed to 2D PIV!
started 1983
……
USA, CornellReynolds number
some 3D-PTV groupsDenmark, Risøparticle dispersion
Switzerland, ETHvelocity derivatives
and many more groups:Eindhoven,Tel Aviv,Göttingen,
list of technical aspects
•flow tracers•illumination•cameras•observation volume•camera callibration•particle detection•from 2D to 3D positions•particle tracking
flow tracers
high tech, accurate, expensive:
Idea: Søren Ott & Jakob Mann, Risø, Denmarkfly ashsieving50-60µm
low tech, accurate, cheap:
illumination
LED array, TU/e
Lorenzo del Castello, Herman Clercx
trend towards smarter solutions
fast digital cameraspixel: 500x500frame rate: 50Hz
pixel: 1000x1000frame rate: 5000Hzorpixel: 250x250frame rate: 80’000Hz
data storage is main bottelneck
particle detection and position
typically the ’image situation’ is far from ideal
camera callibration•teach the cameras with know grid points•problem: how to have space filling target?•solution in part: callibration on flow tracers
from 2D to 3D position
Cam
era
4C
amer
a 3
Cam
era
1C
amer
a 2
x
yz
r(x,y,z,t)
callibration and 2D position accuracy, seeding density, etc.
tracking through consequtive images
tracking criteria:particle must not travel furtherthan their typical spacing
codes available at www.3dptv.schtuff.com
overcome seeding density bottelneck?
K. Hoyer, M. Holzner, ETH
Scanning PTV
idea:scan flowwith thicklaser sheettoget more particles
many dependencies, many choices…
field of view
depth of view opticalworking distance
camerapixel resolution
camerarecording rate
illumination
flow speed
flow scalesone would liketo resolve
particlediameter
number oftracer particles
trackability
final output is the start for analysisif all goes well, one can finally start ’learning’ about the flow
velocity derivativesdifferentiate
convoluted velocity fieldto get
velocity derivatives
challenge to getHIGH SEEDING DENSITY
B. Lüthi ETH, Søren Ott Risø
applicationsflows with:
•turbulence•dilute polymers•2-phases•convection•agregation•reactions•mean shear•entrainment•rotation•bio-medical conditions
emphasis on:
•velocity•velocity gradient•acceleration•dispersion•multi particle
•Lagrangian aspects•(mean) Eulerian flow field
challenge: reach higher Reynolds numbers at full spacial resolution
Some selected outcome