The Effects of Subsonic Microjets on Turbulent Properties in Dump Combustors
- Paper number
IAC-07-C4.I.06
- Author
Ms. Karima Russell, University of Illinois at Chicago, United States
- Coauthor
Mr. Kaustav Sengupta, University of Illinois at Chicago, United States
- Coauthor
Dr. Farzad Mashayek, University of Illinois at Chicago, United States
- Year
2007
- Abstract
Fluidic control of shear layers in air-breathing liquid-fuel combustors is essential for better performance. The increasing demand for compact combustion accompanied by low drag, high turndown ratio, and a reliable flame anchor calls for concurrent application of advanced control strategies such as counter-current shear and microjets. Traditional flame holders, such as the rearward-facing dump combustor, provide a protective environment for the flame to reside. But these systems also carry a significant thrust penalty. The focus of this research is to explore the role of microjets as a shear layer control strategy in dump combustors. The goal is to design a compact, low drag, unconventional combustor that will ensure a stable flame which can be used for air-breathing liquid-fuel systems. Microjets have been successfully applied to jet exhausts for noise reduction. Studies have shown that with the appropriate injection strategy, microjets can lead to a reduction in turbulence intensity within a free shear layer. This is essential for suppressing noise sources in jet exhausts. However, the role of microjets within practical combustion systems is quite different and has remained largely unexplored. In such a scenario, microjets would be used to increase turbulence levels and spanwise non-uniformity within the reacting shear layer at a minimum strain rate penalty. Preliminary studies have indicated that microjets can potentially alter the shear layer characteristics to promote higher heat release and inhibit thermo-acoustic instabilities. Simulations have been conducted within the Reynolds-averaged Navier-Stokes (RANS) framework in a 3D geometry. Results have shown that near the step wall, vorticity (or strain rate) is the primary driving force of turbulent production. Whereas, downstream from the step wall, shear is the driving mechanism of turbulent production. Increasing the mass flow rate of the microjets has been shown to increase non-uniformity in the turbulent flow field, which is ideal. In a turbulent reacting flow field, non-uniform, convoluted structures lead to higher heat release rates. Microjets can also affect the recirculation zone, thus influencing flame stabilization. Many parameters such as the location, size, momentum ratio, and injection angle of the microjets determine the overall performance. Therefore, a detailed parametric study will be the primary focus of this work. Numerical results for the microjets will be compared with ongoing experiments for validation.
- Abstract document