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Submitted by Abbie
11 Jan 2022

Dynamic Particle Imaging Velocimetry (DPIV) for flows visualization using an Industrial Vision Camera such as the Vieworks VC-4MC-M180 can be used to obtain the time dependent velocity distributions in a Field-Of-View (FOV) of single and multi-phase flows which are very fast, turbulent and complex.   DPIV is very useful for analysis of turbulent flow, transient flow, micro flow and 3D volumetric flow studies.  The fast frame rate (180 FPS) of the VC-4MC-M180 allows visualization of laminar separation bubble found in the flow over an airfoil, turbulent flow near an object or complex flows found in bioreactors.

DPIV Applications

To facilitate visualization of a flow, most applications require seeding the flow with tracer particles.  These tracer particles will be very visible in the flow when pulsed with a sheet or spot laser illumination. The laser illumination is very short in duration, easily stopping all motion.  When the laser illumination is off, the image is completely dark.  The short intense laser pulse provides an excellent contrast to the tracer particles after capture.  The tracer particles can then be tracked for movement in the flow where each image is analyzed for the position of these particles as a function of time. Knowing the precise time (Dt) between the double laser pulse provides a reference for the spacing and direction change between these particles in the image sequence.

PIV System Block Diagram with a Vieworks VC-4MC-M180 Camera

A technique called frame straddling is timed & produced by a pulse laser and the Vieworks VC-4MC-M180 camera to capture image pairs that have an extremely short time interval between images.  Using either a diode-pumped Nd:YLF or Nd:YAG laser, the laser is pulsed twice, straddling the two frames as shown below.

PIV Timing Diagram

To setup the Vieworks VC-4MC-M180 camera for PIV, set the FOT register to the minimum value (5).  This sets the intraframe time to 8 us between image pairs, the frame straddling time.  Set the camera into Ext. Trigger mode & use the Trig IN Pos from the Pulse Generator.  The Strobe Out provides a signal with the timing of Delay Trig / 2.  Set the Strobe Out Delay to the time needed to trigger the laser such that the pulse straddles the frame as shown above.