Investigation of a turbulent spot using multi-plane stereo PIV

Abstract

The multi-plane stereo PIV (MSPIV) technique has been applied to an investigation of the spatial and temporal development of turbulent spots in a laminar flat-plate boundary layer flow with a slight adverse pressure gradient. The spot was induced by a locally blown injection at Re = 318 calculated, with x as the distance from the leading-edge, and the measurement volume was located at different downstream positions, at Reynolds numbers between 448=Re=550. For the calculation of the velocity vectors, 32 X 32 pixel interrogation windows were used, corresponding to a resolution down to 1.6 mm in each direction of physical space. On the basis of a large number of evaluated instantaneous 3- and 2-component velocity vector fields, measured synchronously and separated in space, or with different time separations in one or two planes, the technique enabled the possibility of determining several statistical quantities of fluid mechanical significance: ensemble averages and velocity fluctuations (u´, v´, w´), rms-fields, Galilean accelerations, probability density functions (PDF) and space-time-correlations of the velocity fluctuations, the instantaneous Reynolds stresses (u´v´) of all four quadrants and the y-component of vorticity.