Large Scale Turbulent Round Free Jet Far Field Investigations Using Shake-The-Box 3D Lagrangian Particle Tracking

Abstract

In this study, we utilize the Shake-The-Box (STB) Lagrangian Particle Tracking (LPT) algorithm to conduct large-scale measurements in the far field of a turbulent jet. We confirm self-similar mean velocity and Reynold stress profiles across two fields of view (FOVs) spanning 90 to 240 nozzle diameters in streamwise direction. Furthermore, the utilization of a novel version of the data assimilation scheme FlowFit enables the visualization of instantaneous realizations of coherent structures in terms of Q-values. The results indicate that the structures are predominantly tube rather than hairpin-like. The high number of tracked particles and the extensive measurement range allow for the estimation of mean dissipation as a function of the distance from the nozzle using structure functions. A comparison of results derived from longitudinal and transverse approaches with those obtained using the velocity-acceleration structure function indicates that the latter provides more accurate results due to its validity in anisotropic flows. However, the findings also indicate that the anisotropy diminishes downstream. The determination of mean dissipation and acceleration enables the investigation of the validity of the Heisenberg-Yaglom relation in this anisotropic flow. Nevertheless, acceleration is a highly intermittent value, which hinders capturing all relevant events to measure its variance accurately. This paper presents the difficulties encountered in the tracking and filtering of the trajectories, offering a perspective on potential future solutions to the problem.