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.
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
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 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
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
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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