Development of a time resolved scanning particle image velocimetry system for measurement of the small scales of turbulent flows

Our knowledge of the quasi-universal intermediate and small scales of turbulent shear flows is incomplete and is a common topic of great interest in modern turbulence research. The temporal and spatial complexity of the turbulent flows at such small scale has prevented the acquisition of full experimental data sets for validating classical turbulent theory and direct numerical Simulations (DNS). To better understand these phenomena, a Time Resolved Scanning PIV system was developed to take three- dimensional two- component velocity data at the small scales of turbulent flows. The TR SPIV system was designed, set-up and tested. A criterion based on the PIV nature of the measurements and basic turbulence concepts is proposed for the determination of the minimum turbulent scales that the system can measure. Quasi-instantaneous volumetric vector fields at the far field of a round turbulent jet in water (Re~1,500) were reconstructed and studied. The spatial and temporal resolution of the system allowed the visualization of velocity fields at Taylor length scales of the flow and its evolution in time. According to the quasi-universality theory on turbulent inner scales, the inner-variables scaling become Reynolds independent, and this was validated with the probability density functions of the velocity gradients.M.S.Includes bibliographical references (p. 113-114)by Maria del Mar Torregros