Multitime structure functions and the Lagrangian scaling of turbulence

Abstract

We define and characterize multitime Lagrangian structure functions using data stemming from two swirling flows with mean flow and turbulent fluctuations: A Taylor-Green numerical flow and a von Kármán laboratory experiment. Data is obtained from numerical integration of tracers in the former case and from three-dimensional particle tracking velocimetry measurements in the latter. Multitime statistics are shown to decrease the contamination of large scales in the inertial range scaling. A timescale at which contamination from the mean flow becomes dominant is identified, with this scale separating two different Lagrangian scaling ranges. The results from the multitime structure functions also indicate that Lagrangian intermittency is not a result of large-scale flow effects. The multitime Lagrangian structure functions can be used without prior knowledge of the forcing mechanisms or boundary conditions, allowing their application in different flow geometries.