The design and operational development of gas turbine combustors is a complex process, involving a great volume of design and experimental work. The application of computational fluid dynamics (CFD) methods allows to lower the volume of experimental works on operational development of combustors and to make changes to the design of combustion chambers on early design stages. In this paper the application of commercial CFD package CFX-TASCflow for calculation of flow structure and analysis of nitric oxide formation process in the combustion chamber of the PS-90A gas turbine and its modifications is considered. The results of the analysis show, that the basic determinative criterion of a nitric oxide emission level is the residence time of a combustion products in high-temperature zones. With help of this criterion, an optimization of the PS-90A combustion chamber was performed. A design of an optimized combustion chamber allows to achieve a low level of nitric oxide emissions.

Modern concepts for reducing thermal NO emissions require the use of very lean fuel/air mixtures. Therefore a problem of lean quench should be solved during design process of gas turbine combustor and it’s operational development. Since maintenance of flame stability for wide range of gas turbine engine operational modes is essential, therefore there is a great demand for models which are able to predict lean blow out limits of turbulent, premixed and partially premixed, aerodynamically stabilized flames. In this paper a model describing flame destabilization process is presented. This model takes into account various physical processes, which lead to flame destabilization. The model is based on equation for reaction progress variable. An expression of source term of this equation contains turbulent flame speed, which is calculated with the use of Zimont’s formula modification, proposed by authors. The results of simulation were compared with test results for our lean premixed combustor. Fuel mass flow rate of pilot zone was decreased during test until heat release of pilot flame front became insufficient and couldn’t support a combustion process in a lean premixed zone. Our simulation with modified model allows to get prediction of lean blowout limit.

Most of the modern combustor’s designs use staged concepts for reducing thermal NO emissions. Usually, a combustion process takes place inside the main zone, which uses very lean premixed fuel/air mixtures. A diffusion pilot zone supports combustion process inside a lean main zone. Thermal NO formation process takes place predominantly inside hot diffusion flame. So, operation modes of pilot and main zones must be arranged to provide low NO emissions of pilot zone and maintain flame stability inside the main zone simultaneously. In this paper a concept of new turbulent model combustion model is presented. This model allows to model diffusion and premixed flames and takes into account various physical processes, which lead to flame destabilization. The model uses an equation for reaction progress variable. In the frameworks of considered approach this equation has three source terms. These terms are responsible for different conditions of combustion process: diffusion flames, premixed flames and distributed reaction zones. A proposed model was widely validated for different types of combustion chambers such as: 1) Bluff-body flameholder (lean premixed combustion: modeling of lean blow out); 2) Conventional diffusion regime of combustion chamber of gas turbine engine (modeling of flame stabilization and NO emissions); 3) Combined combustion regime of combustion chamber: burning process is inside pilot diffusion and main premixed zones (NO emissions and lean blow out limits for several operational modes). These tests had shown a good agreement of experimentally obtained data with results of simulations.

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A combustor is a crucial unit of gas turbine engine because it should work reliably at high temperatures; provide a suitable temperature distribution at entry to the turbine and supply a low emission level of harmful substances. An operational development of combustors is a very complex process, involving a great volume of design and experimental work. The application of computational fluid dynamics (CFD) methods allows to decrease the volume of experimental works on operational development of combustors and to make changes to the design of combustors on early stages. This paper describes development and validation of CFD-based analysis methodology, used to predict NOx emission level for different types of gas turbine combustors. This methodology includes comprehensive modeling of physical and chemical processes that take place in gas turbine combustors: turbulent flow of reacting gases, heat transfer, chemical kinetics and formation of nitric oxide. To simulate these processes the following mathematical models were used and validated: • Navier-Stockes equations; k-ε RNG, k-ε RSM, k-ω SST turbulence models; • Flamelet and Flamefront combustion models; • Different chemical kinetics mechanisms, describing methane and aviation kerosene oxidation processes; • Diffusion radiation model and discrete ordinates method to calculate radiation heat fluxes; • Extended n-heptane oxidation mechanism to simulate PAH and soot formation; • Prompt and thermal NO formation mechanisms; • Wide band exponential model for gases and empirical correlation for soot to calculate radiation properties of medium. Different factors that affect NOx formation process are considered. They include O and OH prediction methods, influence of radiation heat transfer, and choice of combustion and turbulence models. Developed methodology was used to simulate combustion process in gas turbine combustors that use RQL, LPP, wet NO technologies of low NOx combustion. Merits, demerits and peculiarities of considered low NOx combustion technologies are discussed. According to the results of the analysis, the most efficient technology for NOx reduction was selected.