Coherent Structures in Turbulent Flows: Experimental Studies on the Turbulence of Multiphase Plumes and Tidal Vortices

• Main Author: Bryant, Duncan Burnette
• Other Authors: Socolofsky, Scott A.
• Format: Others
• Language: en_US
• Published: 2011
• Subjects: Plumes; Vortex; Tides
• Online Access: http://hdl.handle.net/1969.1/ETD-TAMU-2010-05-7893

This dissertation presents the turbulence of multiphase plumes and tidal vortices by studying and quantifying coherent structures that affect the dynamics of the flow. The measurements presented in this dissertation were taken using particle image velocimetry (PIV). After preprocessing the images and conducting the PIV analysis to get the final velocity fields, the local swirl strength was used to identify coherent structures (vortices) in the flow. This dissertation used the identified vortices to quantify the turbulent properties of the flows. The mean and turbulent properties of bubble plumes are found to be self-similar within the measured air flow rates when appropriately nondimensionalized. The timeaveraged velocity profile was shown to have a Gaussian distribution when nondimensionalized by the centerline velocity and plume radius. The bubble plumes were found to have the most energetic vortices along the plume edge and a modulated turbulent energy spectrum with a slope in the inertial subrange from -7/6 instead of the classical -5/3. The mean and turbulent properties of an inertial particle plume are presented, revealing the time-averaged velocity and vorticity profiles to be self-similar for all cases when nondimesionalized by the centerline velocity and plume radius. The average vortex properties were not self-similar for all flow cases with the largest two particles sizes being self-similar and the smallest particle vortex properties being similar to bubble plume data. Despite the difference in vortex properties, the turbulent energy spectra in inertial particle plumes followed the same modulation as the bubble plumes. PIV experiments from the tidal starting-jet vortices detail the influence of a finite channel length using identified vortice. The results show the trajectory and development of the tidal starting-jet vortices to be changed by a region of vorticity that develops inside the channel and is expelled as a vortex during the ebb tide. This expelled lateral boundary layer vortex is shown to move the starting-jet vortex away from the tidal jet shear layer thus reducing the input vorticity. When the expelled boundary layer vortex strength is 1/5 the starting-jet vortex the system dynamics change resulting in a deviation in the starting-jet vortices' trajectory. This dissertation successfully uses the local swirl strength to quantify the turbulence of multiphase plumes and tidal starting-jet vortices. Using these results, engineers will be able to better predict the efficiency of CO2 ocean sequestration and tidal flushing. Furthermore, the techniques of quantifying coherent structures developed in this dissertation can be applied to a multitude of turbulent flows.