Generation and Decay of High-Intensity Turbulence
Mentor:John LaRue, Professor , UC Irvine
The combustion process in a gas turbine is not perfect; incomplete mixing causes inefficiencies in the chemical reaction and produces pollution in the form of Mono-Nitrogen Oxides (NOx). In power plants, a gas-turbine pre-mixer is used to mix fuel and air prior to combustion. High-intensity turbulence promotes uniformity of the mixture and increases the rate of mixing. The goal of this study is to provide laboratory data on the velocity and root-mean-square variance of the mixing process. We will create high-intensity near-homogeneous near-isotropic turbulence and study the downstream turbulent decay of the flow. This is accomplished with the use of the UCI wind tunnel and an Active-Grid turbulence generator, an apparatus of randomly spinning diamond flaps. In order to homogenize the turbulent flow further and promote the onset of isotropy sooner, the turbulence generated by the active grid may be attenuated with the use of manipulators, such as wire screens of different solidity and mesh size, a passive grid, or a combination of both. The velocity profile showed that the variance of mean speed along the vertical profile at the entrance and exit of the test section was 2.0% and 1.1%, respectively. A power law curve fit of the turbulence intensity versus normalized downstream position was found to have a decay coefficient of 4.1 and a decay exponent of 1.3. The decay exponent is comparable to traditional, low intensity grid-generated turbulence even though the decay coefficient was significantly higher.