Computational Modeling of Coupled Acoustic and Combustion Phenomena Inherent to Gas Turbine Engines

ABSTRACT:The pressure oscillations associated with thermoacoustic combustion instabilities are a serious hazard to combustion systems such as gas-turbine-engine combustors, augmentors / afterburners, ramjets, and rocket engines. Unfortunately, combustion engineers currently face a dilemma when trying to estimate these potentially destructive phenomena. Engineers can obtain a quick insight into these instabilities with tools of very limited predictive capability, or they can use CFD, which can be deemed predictive but is too computationally expensive for practical use. A tool must be developed to bridge this huge gap in predictive capability and computational cost. With this in mind, Combustion Science & Engineering, Inc. will develop a software suite to estimate thermoacoustic combustion instabilities that will use a novel CFD / acoustic-solver strategy. This hybrid strategy uses mature concepts from CFD, acoustics modeling, and multiscale methods not applied yet to problems in combustion instabilities. Although this strategy is not trivial to implement, it can be developed in 2 years with a high probability of success. This software suite will also be able to conduct classic analyses and CFD simulations, providing combustion engineers with a well-rounded tool. At the end of Phase II, a software suite will be validated and ready for beta testing.BENEFIT:An important product from this project will be a suite of computational tools to analyze the thermoacoustic behavior of augmentors and combustors. These modeling tools can be used for a variety of applications, including the design and testing of these systems. This will be an important design tool for most propulsion systems, including gas turbines applications, for predicting combustion instabilities. This suite of modeling tools is very versatile such that the user can conduct a variety of analyzes of varying complexity and operating conditions. This product will give the design engineer much more freedom to test new combustor designs operating at wider range of pressures, temperature and fuel / air mixtures. The software suite proposed here will bridge a current gap in predictive power to estimate combustion instabilities and, consequently, will have a broad range of applicability, something which contrasts with traditional combustor-dependent tools. As a result, the proposed software will be readily useful to a wide range of combustion systems of interest to the military, such as gas-turbine-engine combustors, augmentors/afterburners, and ramjets, all of which are prone to the damaging pressure oscillations associated with combustion instabilities. Gas-turbine-engine combustors are widely used in the military since they are the prime movers of aircrafts, tanks, and some combat ships. Regarding augmentors/afterburners, these devices are of military importance because aircrafts use them to obtain bursts in thrust, such as those needed during takeoff, climb, missile evasion, and combat maneuvers; some of the aircraft in service that use augmentors include the F15, F16, F18, F22, and F35 (still in production). There is a need for tractable, design-specific thermoacoustic analyses in the gas-turbine community. This software will be used by both the design and testing communities. The product developed in this work will be a useful tool for subsonic, supersonic and hypersonic vehicle design applications for the US Air Force. Discussions with engine design teams indicate that the capabilities of this project will greatly enhance current design tools in use by equipment manufacturers. Also the market for this product will include gas turbine designers and manufacturers for both military and civilian aircraft. The use of this tool will significantly reduce development costs by eliminating some design iterations and hardware testing, which is quite expensive and time-consuming. This tool will be applicable to any propulsion system that utilizes combustion for energy input, including afterburners or augmentors, interturbine burners or any new concept for increasing gas turbine efficiency and power. In addition, the capability to model thermoacoustic processes is also important in a variety of stationary power generation applications, including large gas turbines used for electrical power generation or microturbines used for distributed power generation. Furthermore, this capability is useful to other combustion systems, such as used in boilers or furnaces.