Particle Image Velocimetry

Product catalog summary

Introduction
Particle Image Velocimetry (PIV) is a non-intrusive measurement technique used to obtain instantaneous velocity fields in two-dimensional regions of gas or liquid flows. This document provides an overview of the setup, evaluation, and advanced configurations of PIV systems.

Setup
In PIV, light scattering particles are added to the flow. A laser beam is formed into a light sheet that illuminates these particles twice within a short time interval (Δt). The scattered light is captured on two consecutive frames by a high-resolution digital camera. This setup can be applied in various configurations, including microscopic, endoscopic, and macroscopic, suitable for both gaseous and liquid media.

Evaluation
The captured particle images are divided into small interrogation windows. For each window, the average particle image separation (Δx, Δy) is determined using cross-correlation and localization of the correlation peak. The velocity components (u, v) in each window are calculated using the formula: u=(1/M)(Δx/Δt) and v=(1/M)(Δy/Δt), where M is the magnification of the camera.

Tomographic PIV
Tomographic PIV systems, typically using 2-4 cameras, extend flow measurement into a full volume. This involves tomographic reconstruction of voxel intensities for each time step, followed by 3D3C-cross-correlation between interrogation volumes. This method allows for the instantaneous measurement of all three velocity components in a three-dimensional measurement volume, visualizing the 3D flow structure.

Spatial Derivatives
From the velocity field, various spatial derivatives such as vorticity, shear stress, and turbulent energy can be derived. Capturing and computing a sequence of images provides insights into the temporal behavior of the flow.

Stereo PIV
Stereo PIV uses a second camera and stereoscopic imaging to measure all three velocity components within a two-dimensional field of view. After image calibration, the three components of the velocity vector are derived from the two displacement projections. Scheimpflug lens arrangements ensure all areas of the image plane remain in focus.

Catalog excerpts

Particle Image Velocimetry PIV is a non intrusive measurement technique used to obtain instantaneous velocity fields in a two dimensional region of gas or liquid flows. Spatial derivatives Light scattering particles are added to the flow. A laser beam The particle image is subdivided into small interrogation From the velocity field a range of spatial derivatives can be All three velocity components inside a two dimensional field A Tomographic PIV system with typically 2-4 cameras extends is formed into a light sheet illuminating seeding particles windows. For each interrogation window the average derived such as vorticity, shear stress and turbulent energy. of view can be measured using a second camera and stereoscopic the flow measurement into a full volume. Processing is done by twice with a short time interval Δ The scattered light is t. particle image separation (Δx, Δy) is determined by cross- Capturing and computing a sequence of images can provide imaging. After image calibration the three components of the tomographic reconstruction of voxel intensities for each time recorded onto two consecutive frames of a high resolution correlation and localization of the correlation peak. When M information about the temporal behavior of the flow. velocity vector can be derived from the two displacement step followed by 3D3C-cross-correlation between interrogation digital camera. Microscopic, endoscopic and macroscopic is the magnification of the camera the velocity components projections. Scheimpflug lens arrangements keep all areas volumes. This allows for instantaneous measurement of all configurations cover a wide range of applications in gaseous (u,v) in this interrogation window is given by u=(1/M)(Δx/Δt) of the image plane in focus. three velocity components in a three dimensional measurement Downsview House / Grove Technology Park / Grove, Oxon, OX12 9FF / UK E-Mail: [email protected] / www.lavisionuk.com Tel. +44-(0)-870-997-6532 / Fax +44-(0)-870-762-6252 volume (3D3C) visualizing the 3D flow structure. LaVision GmbH Anna-Vandenhoeck-Ring 19 / D-37081 Goettingen / Germany E-Mail: [email protected] / www.lavision.com Tel. +49-(0)551-9004-0 / Fax +49-(0)551-9004-100 211 W. Michigan Ave. / Suite 100 / Ypsilanti, MI 48197 / USA E-Mail: [email protected] / www.lavisioninc.com Phone: (734) 485-0913 / Fax: (240) 46

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