Effects of Swirl Number on Swirled Spray and Flame Characteristics at Small Confinement Ratio

Distributed lean direct injection（DLDI）combustor is a development form of multi-point lean direct injection（MLDI）combustor. The elemental main-stage LDI injector of the DLDI combustor was studied in this paper. Effects of the swirl number（Sn）of the outer swirler varying from 0.65 to 0.33 on the flow field，the spray dispersion and flame characteristics have been studied. The commercial software FLUENT was used to simulate the flow field by using the RANS method. The DPM（Discrete Phase Model）was used to simulate the spray dispersion. Mie scattering and Laser-particle-sizer were used to measure the spray dispersion and SMD，respectively. The accuracy of simulation calculation can be checked by measured results. The high-speed camera was used to capture the flame structure. Results show that the flow field distribution is directly affected by the change of the swirl number. With the decrease of swirl number，the outer swirling air jet makes a stronger suppressing effect upon the inner swirling air，which leads to the both decrease of the opening angle of the inner swirling air and the size of the center recirculation zone. Especially when Sn=0.33，the corner recirculation zone gradually evolves into the wall recirculation zone. Changes of the flow field affect the spray distribution. When Sn varies from 0.65 to 0.38，the spray core is mainly dispersed under the transportation of the inner swirling air jet，due to which the opening angle is determined by characteristics of the inner swirling air jet. When Sn=0.33，the spray can inject into the outer swirling air jet under the inertia effect，and then distributed by the simultaneous action of the outer swirling air jet and the wall recirculation zone. It can be concluded that it is benefit for even spray distribution when the spray core can inject into the outer swirling air jet. Flame structure shows that at small confinement ratio，when Sn=0.33，the small recirculated air flow rate reflects the poor recirculation capability of the center recirculation zone，which cannot hold the flame. At this time，the wall recirculation zone can help to hold the flame. © 2022 Journal of Propulsion Technology. All rights reserved.