Particle Image Velocimetry


Particle Image Velocimetry, otherwise known as PIV, is an optical method widely used in flow visualization and fluid dynamics research. PIV provides detailed measurements of velocities, vectors and related properties in fluids.

The technique is 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. PIV is very useful for analysis of turbulent flow, transient flow, micro flow and 3D volumetric flow studies. As an example, the high temporal rate allows visualization of the laminar separation bubble found in the flow over an airfoil, turbulent flow near an object or complex flows found in bioreactors.

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 between the double laser pulse provides a reference for the spacing and direction change between these particles in the image sequence. The particles are plotted as a series of velocity vectors representing the flow at a given instant in time.

For years, high-speed imaging has been utilized in the following industries for PIV research and analysis: Automotive, Aerospace, Biotech and Medical, Marine Propulsion, and Electronics.  There are several companies that manufacture high-speed cameras, so how do you decide which company to buy from and which model of camera to buy? There are a couple factors that are important to consider when purchasing a high-speed camera for PIV applications, including frame rate, light sensitivity, resolution, and  interframe time.

Phase Image-based Particle Tracking Velocimetry using Digital Holographic Microscopy
Three-dimensional particle detection scheme with phase image is developed for a particle tracking velocimetry system to measure the velocity fields. The accuracy of the present method is demonstrated by the measurement of Poiseuille flow.

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Tomographic Particle-Image Velocimetry Analysis of the Influence of Artificially Introduced Sound Waves on Transonic Buffet Flow
The scope of this study is to investigate how the feedback loop that leads to the buffet flow and of which the trailing-edge noise represents the upstream propagating part can be influenced by artificial noise that is introduced to the flow in the trailing-edge region of a supercritical airfoil under buffet flow conditions. The airfoil flow is investigated at a freestream Mach number of M∞ = 0.73, an angle of attack of α = 3.5°, and a chord based Reynolds number of Re∞ = 1.89∙106 . Sound waves with a well defined frequency fsound and variation of the sound pressure level (SPL) with a frequency of fSPL are generated by a loudspeaker downstream of the airfoil. Time-resolved tomographic particle-image velocimetry as well as unsteady pressure measurements are used to investigate the unsteady transonic buffet flow field with and without artificial sound waves to quantify their influence on the buffet phenomenon.

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Hydrodynamic structure of a bubbly flow in an annular channel: experimental study by means of PIV/PFBI/PTV
In the paper, an experimental investigation of the local structure of a bubbly upward flow in an annular channel was carried out by means of a combination of PIV/PFBI/PTV techniques. PIV was applied to measure velocity distributions and turbulent characteristics in the continuous phase, PFBI approach was applied to visualize bubbles in the flow and evaluate their positions and sizes and the simplest PTV method was employed to determine the bubble velocities. The flow was studied at the Reynolds number of 12,500 and different void fractions β = 0, 1 and 2%. The mean air bubble diameter was estimated to be about 0.8 mm for all β. Bubble concentration was observed to increase near the channel walls. Rising velocity of the gas bubbles was measured in various locations across the annulus duct and it was found that it is substantially higher for the bubbles moving in the central part of the channel.

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