Brownian motion and correlation in particle image velocimetry

In particle image velocimetry applications involving either low velocities or small seed particles. Brownian motion can be significant. This paper add resses the effects of Brownian motion. First, general equations describing cross-correlation particle image velocimetry are derived that include: Brow nian motion. When light-sheet illumination particle image velocimetry (PIV) is used Brownian motion diminishes the signal strength. A parameter descri bing this effect is introduced, and a weighting function describing the con tribution to the measured velocity as a Function of position is derived. Th e latter is unaffected by Brownian motion. Microscopic PIV Brownian motion also diminishes the signal strength. The weighting function for microscopic PIV is found to depend on Brownian motion, thus affecting an important exp erimental parameter, the depth of correlation. For both light-sheet illumin ation and microscopic PIV, a major consequence of Brownian motion is the sp reading of the correlation signal peak. Because the magnitude of the spread ing is dependent on temperature, PIV can. in principle, be used to simultan eously measure velocity and temperature. The location of the signal peak pr ovides the velocity data, while the spreading of the peak yields temperatur e. (C) 2001 Published by Elsevier Science Ltd.