View of the SAFL building from the river
December 17, 2013


Analysis of Turbulent Flow Generated by an Oscillating Grid

Chao Sun, MS candidate in civil engineering
Advisor: Michele Guala, Assistant Professor of Civil Engineering, St. Anthony Falls Laboratory, University of Minnesota

In natural environment, it is very common to have turbulent flow behaviors in the same fluid body. Turbulence in a water body is a major factor for the movement and growth conditions of water-borne microorganisms. Although no microorganism is applied in this research project, it provides a baseline model for future investigation. Temperature stratification is created in order to mimic a natural lake environment, comparing to the non-stratified temperature condition. The turbulence is created by an oscillating grid in order to mimic wind or other activities near the surface of a lake, comparing between different grid durations and frequencies. An important question is proposed that how fast the turbulence can affect or mix the layers across the thermocline with the temperature stratification.

In the purpose of tracking particles and analyzing turbulence in a water body, a series of experiments using designated equipment and devices have been performed to measure temperature stratification, track particle movement and distribution. The experiments are performed in a vertical water tank called Plankton Tower (PT) where turbulence is created by an oscillating grid in the water body near surface. This project employs a system of particle image velocimetry (PIV) to illuminate and track particles. Thus, turbulence flow behaviors can be carefully examined under different conditions by controlling grid frequency, grid running duration and temperature stratification. With the acquired the data, velocity vectors, velocity profiles, velocity fluctuations, vorticity and energy dissipation can be calculated and analyzed.

Furthermore, this project introduces a preliminary investigation on three-dimensional particle tracking velocimetry (3D-PTV) in the sole purpose of exploring new techniques for future reference.