2-Dimensional (2-D) Particle Imagery Velocimetry (PIV)

Description:

To visualize the flow distributions the Federal Highway Administration's Turner-Fairbank Highway Research Center J. Sterling Jones Hydraulics Research Laboratory uses a non-invasive measurement technique called PIV.  This involves the use of microscopically small, highly reflective particles are added to the flow to aid in analysis. Then a laser illuminates a thin layer of the flow so that only the particles in that light sheet reflect the laser's light. With 2-D PIV one camera is mounted orthogonally to the light sheet and captures images. Using two succeeding images and an algorithm based on statistical probability allows us to determine the speed and the direction of the moving particles. Understanding that the particles move with the same velocity as the flow, allows us to determine the velocity. As already mentioned, with PIV there is no need for inserting a probe to flow. Therefore the flow remains undisturbed. A disadvantage of the 2-D PIV technique is that only two components of the direction of the velocity are determined. Using a 3-D PIV System solves this problem.

Diagram of a 2-D PIV system	Photograph of a 2-D PIV system measuring velocities around a group of cylinders

We are using the 2-D PIV technique to visualize cross sections of a bridge deck, which is submerged by water to determine the effective flow depth.

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