Yoshiharu Nonaka

Numerical Simulation of Flame Propagation in a Staged Combustor

Highly unsteady flow fields are generated in recent low-emissions gas turbine combustors. Numerical simulation of such flows using conventional numerical code using a time-averaged turbulence model is difficult and time-accurate LES (Large Eddy Simulation) is expected to predict them. Calculation of turbulent combusting and non-combusting flow field in a staged combustor were conducted using LES. To validate the LES calculation, a prediction of time-averaged velocity field is compared with those by an experiment and a conventional numerical method based on RANS model. Turbulence intensity affects flame speed so much that velocity fluctuations were measured to obtain turbulence intensity in the non-combustion test. Strongly turbulent regions between the pilot and main stages, which are important for the flame propagation, were simulated. The combustion was calculated using a laminar flamelet model and the flame propagating phenomenon was simulated properly, which is impractical by the conventional simulations using time-averaged turbulence models. The feasibility of the LES calculation is discussed.© 2002 ASME

Large-Eddy Simulation of Turbulent Combustion in Multi Combustors for L30A Gas Turbine Engine

When designing a combustor, numerical analysis should be used to effectively predict different performances, such as flame temperature, emission, and combustion stability. However, even with the use of numerical analysis, several problems cannot be solved by investigating single combustors because, in an actual engine, interactions occur between multiple combustors. Therefore, to evaluate the detailed phenomenon in an actual combustor, the interactions between all combustors should be considered in any numerical analysis. On the other hand, a huge amount of computational cost is required for this type of analysis. Here a large-eddy simulation employing a flamelet/progress variable approach is applied to the numerical analysis of industrial combustors. The combustor used for this study is the L30A from Kawasaki Heavy Industries, Ltd. Computations are conducted with a supercomputer (referred to as the “K-computer”) in the RIKEN Advanced Institute for Computational Science. All combustors in the L30A engine (from the compressor outlet to the turbine inlet) are simulated, including the fuel manifold. This engine has eight can combustors that are connected through the fuel manifold and compressed air housing unit. The total number of elements is approximately 140 million. The flow patterns for each combustor are similar in all cans. A swirling flow from the main burner is formed and accelerated by the supplemental burner. There is a high-temperature region before the supplemental burner. The flow field and temperature distribution in an actual combustor interacting with other combustor cans are simulated adequately. The mass flow rate of the air and those of the fuels are distributed equally for each can. Therefore, the outlet temperature difference for each can is also very small.Copyright

Large-Eddy Simulation in an Industrial Gasturbine Combustor for NOx Prediction

NOx emission reduction is important for developing gas-turbine engines. Predicting the thermal profile and pollutant-emission factor by numerical simulation is effective for reducing the development costs. Here a large eddy simulation coupled with a 2-scalar flamelet approach is applied to the numerical analysis of an industrial gas-turbine combustor. The combustor of an L20A-DLE gas-turbine engine is calculated. Combustor performance under different loads is investigated. NOx production decreases with reducing load, and this tendency agrees well with the experimental results. It is said that NOx production due to a large amount of supplemental burner fuel. NOx production in the simulation is lower than in the experiment. The simulated temperature in the combustor outlet is also lower than the adiabatic temperature. Moreover, the fuel is not burned completely within the combustor region. The difference in the combustion status in a supplemental burner is investigated. For the diffusion flame, a high-temperature region is observed locally owing to the presence of a fuel-rich region. For NOx production, NOx emission reduction is expected using a burner that introduces a premixed flame. From the simulation results, we can estimate NOx production in a gas-turbine combustor. The tendencies in the differences of the loads agreed well with the experimental data, and the superiority of a premixed flame was indicated.Copyright

Gas flow simulation and visualization in cylinder of motor-cycle engine

In gasoline engines for motorcycles, there are various restrictions on the intake duct shape imposed by the limitations of the engine mounting space and layout. The intake duct shape (intake port and manifold shape) has a great influence on the in-cylinder flow (swirl and tumble flow). Therefore, the fundamental technologies of flow visualization experiments and numerical simulation are needed for the design of high-performance engines. In this paper, we present good agreement of results by visualization experiments and numerical simulations of in-cylinder flow for such factors as flow pattern and swirl ratio.