AN EXPERIMENTAL AND NUMERICAL STUDY OF TEMPERATURE UNIFORMITY ENHANCEMENT VIA PASSIVE GEOMETRY MODIFICATIONS IN AIR DILUTION MIXING

Abstract

This work studies the effect of passive geometries on the temperature uniformity downstream of gas turbines dilution zones. The experimental setup simulates the non-reacting hot and cold air mixing in a dilution chamber, with inlet Reynolds number in the range of 40,000 – 95,000. Several CFD models were investigated and validated against experimental results. The proposed passive geometries include dilution jet extender parts that are installed on the large dilution holes (5mm to 25mm). The second proposed geometry is converging nozzle parts, called jet area modifiers, installed on the inner side of the large dilution holes. The converging nozzle parts have lengths of 5mm, 15mm, and 25mm and area ratios of 0.5 and 0.75. The presented research investigates the effect of different factors affecting temperature uniformity. Results indicate that temperature uniformity is the strongest factor affecting the usefulness efficiency, followed by the jet extender length. The Reynolds number does not have a significant effect on the usefulness efficiency. Jet extenders offer improvement on the temperature uniformity index by 0.9% - 14.9% depending on the temperature ratio and extender length. The added pressure drop varies between 5% and 28% depending on extender length. Jet area modifiers result in an improvement in the temperature uniformity index between 2% and 29%, and pressure drop of 8%-36% compared to the baseline extender case. The realizable k-ε model showed good agreement with experimental data and performed well against k-ω (SST) and Reynolds Stress Turbulence (RST) models.