Improving the accuracy and resolution of particle image or laser speckle velocimetry

Particle Image Displacement Velocimetry (PIDV) or Laser Speckle Velocimetry (LSV) is a non-intrusive 2-D method of obtaining instantaneous fluid velocities over an extended region. This method involves lighting a particle seeded flow with a sheet of light (usually from a laser) and photographing the particles at two instants of time on the same film. This film is then analyzed to determine the displacement of the particle over the known time interval. Applications of PIDV and LSV have been diverse, including flow past cylinders and airfoils by Lourenco et al. (1986) and Smith et al. (1986), transient Benard convection by Simpkins and Dudderar (1978), vortex pairing in jets by Meynart (1983) and internal gravity waves by Gartner et al. (1986). These studies however, have all been two dimensional. The velocities along the lighted plane were measured, from which the two dimensional vorticity fields and streamlines were calculated using finite differencing (Lourenco et al. 1986, and Smith et al. 1986).