PIV System


LaVision FlowMaster PIV Systems

 

  1. PIV Principle

  2. Time-Resolved PIV

  3. Tomo-PIV


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Integrated Turn-Key Systems with unique Measurement Capabilities

 

The PIV-System is provided by our business partner LaVision.

LaVision designs the most flexible and powerful commercial PIV system family
FlowMaster based on our application knowledge and our tradition of technical
communication with our customers.

LaVision continuously offers the best PIV algorithms for calculation and validation.

windtunnel setup

Typical Stereo-PIV setup consisting of double-pulse laser, two cameras and sheet-optics behind a laser guiding arm, mounted on a portable 2-axes translation stage


PIV PRINCIPLE

The FlowMaster system family is designed to measure instantaneous 2D- and 3D velocity
fields using the well-established Particle Image Velocimetry (PIV) technique. The different types are measurements on a plane/sheet (2D and Stereo-PIV) and in a volume (Tomo-PIV).While 2D-PIV measures both components on a plane, Stereo-PIV measures also the out-of-plane component on a plane. Tomo-PIV measures all three vector components in a volume. For all types the measurements can be performed at either low frame rate ("Low-Speed"-PIV) or at several kHz ("Time-Resolved"-PIV).

The flow is seeded with small particles which follow the flow. Typically a pulsed laser
beam is formed into a light sheet and is fired twice with a short time delay dt. Both
illuminations are recorded by a double-frame high resolution CCD camera.
The recorded image is divided into small interrogation windows typically 64 x 64 down
to 16 x 16 pixels in size. During the time interval dt between the laser shots the particles
of each interrogation window have moved by a displacement ds. The velocity is then
simply given by the ratio ds/dt. The calculation of the particle displacement ds is done
by fast FFT-based cross-correlation of two corresponding interrogation windows.
Additional advanced correlation algorithms are selectable for improved performance
such as local adaptive window shift and deformation and correlation averaging.
The position of the highest peak in the correlation plane indicates the mean
displacement ds of the particles in a particular interrogation window. The
displacement vectors of all interrogation windows are finally transformed
into a complete instantaneous velocity map.

Measurement principle with douible-pulse laser, camera, sheet-optics and the seeded flow Working Principle

Innovative Flow Field Analysis Algorithms for PIV

LaVision provides up-to-date flow analysis algorithms developed in close cooperation with
various PIV research groups. The software is open for user modifications and extensions
based on the built-in CL macro language, which has already been used extensively by
many customers (‚C'-Syntax: source code available).
The flow field analysis algorithms for evaluation of PIV measurements come with the
Data aquisition and Visualisation software package DaVis.
DaVis is the unique software platform for the LaVision FlowMaster PIV systems.
Its modular structure enables an easy to use integration of new algorithms and
user-built macro codes.

 

screenshot-piv


Screenshot of the DaVis control and analysis software


FlowMaster Time-Resolved PIV opens new areas of fluid dynamic analysis. It combines
the spatial information of digital PIV with the temporal evolution of each point.
The system measures velocity and acceleration fields and turbulence quantities of
transient phenomena. The time-resolved PIV information opens a new area for velocity
derivations or correlations in time. With time-resolved PIV the user is able to calculate
temporally dependent quantitative turbulence information. It provides information about:

 

  • time dependence of POD-modes
  • vortex characteristics with time
  • space-time correlations
  • flow element tracking
  • power spectra
  • acceleration fields
  • flow time scales

 

 

Desert Locust
Courtesy: R. Bomphrey, Dept. of Zoology, University of Oxford


Result of a time-resolved tomographic PIV measurement behind a desert locust in a wind tunnel. Shown here is vortex strength

LaVision's FlowMaster Time-Resolved systems include state-of-the-art digital high-speed
cameras with 1, 2 or 4 Mpixel resolution. Up to 16 kHz frame rate at full resolution and
several hundreds of kHz frame rate at reduced resolution are available. Single or dual
cavity high-repetition rate solid state lasers with a wide range of pulse energies can be
selected. All components are integrated and controlled from the DaVis software.
Special correlation algorithms ('pyramid correlation') take advantage of the additional
time information.

Tomographic Particle Image Velocimetry (Tomo-PIV) is a novel technique for 3D velocity
measurements. Velocity information results from three-dimensional particle pattern
cross-correlation of two reconstructions obtained from subsequent exposures. The
technique is fully digital and allows high seeding (information) density and provides dense
vector fields compared to sparse 3D-particle tracking. The method is truly instantaneous
across the volume, as opposed to scanning PIV. Tomo-PIV is suited for fast flows
requiring small dt's between exposures and allows an easy extension to high time
resolution using high speed cameras.
  • turbulence research
  • 3D-flow structure visualization
  • full 3D-vortex analysis
  • flow-structure-interaction

Tomo-PIV measurement


Courtesy: A. Schroeder, German Aerospace Center Goettingen

Result of a tomographic measurement behind a backward facing step in a wind tunnel.





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2D2C FlowMaster System 100x100mm

Particle Image Velocimetry System