No abstract

In the paper, a one-dimensional compressible flow of gas inside the gas turbine’s diffuser has been simulated. The modeling has been performed to the aim of obtaining boundary conditions of outlet gas from diffuser and inlet gas to the combustion chamber. Depending on working flow regimes of fluid including subsonic, transonic, and supersonic flows, changes of diffuser cross-section have different effects on gas flow characteristics. For these effects to be correctly imposed, Mach number of the gas flow in each time-step affected by changes of cross-section would be determined, depending on the local Mach number in the same time-step. Obtaining distribution of Mach number along diffuser length, changes in other main characteristics of flow such as pressure, temperature, speed, and density for all of the points along diffuser length would be obtained. In order to verify the validity of the numerical algorithm used, the gas flow would be solved in a divergent nozzle and compared to other numerical methods. In the end, using gas turbine diffuser’s geometrical information, compressible gas flow inside it would be studied using the actual boundary conditions for a 25 MW gas turbine.

In this paper, a dynamic combustor model for inclusion into a one-dimensional full gas turbine engine simulation model, with high numerical accuracy is developed. Effects of dominant parameters, such as frequency and amplitude of the inlet air and fuel mass flow rate fluctuations, on outlet temperature of the combustion chamber, are investigated. The main goal of this research is to analyze the response of the gas turbine combustor to dynamic events that occur in the compressor. In the present work, for modeling combustion, the equations of chemical equilibrium (a second-law concept) are developed and applied to combustion-product mixtures. Thus the heat released from combustion is computed and used as a source term in the energy equation. Ignition effects either would be considered with a time lag equation as a source term in the energy equation. The combustor flammability limits are determined by using available experimental data for various gases and also Le Chatelier’s law. Source terms of governing equations are added using the operator splitting method. To operate this, the modified version of the PPM algorithm called PPMLR is used which solves the Euler equations in Lagrangian coordinates. At the end of each time step, results calculated in the Lagrangian coordinates would remap to the original Eulerian coordinate. The results revealed that to achieve a grid-independent solution, the accuracy of 0.002 m over the length of the combustion chamber should be applied. By reducing the accuracy of simulation, numerical diffusion causes a rise in flow temperature along with the combustion chamber. Through the dynamic modeling aspect, it is found that by increasing inlet fuel flow rate frequency up to 25 Hz, the amplitude of the fluctuations of outlet temperature, increases. Further increase in frequency up to 100 Hz, the amplitude of the fluctuations remains unchanged. However further increases in frequency from 100 Hz, causes amplitudes of outlet temperature fluctuations to decrease.

In the paper, combustion flammability limits in the combustion chamber of gas turbines and effective factors on these limits would be studied. Considering flammability, initiation of combustion and stability limit are very important parameters in the performance of the gas turbine combustion chamber and to study these factors, flammability of combustion has to be controlled. So, in the paper, the method of calculation of these limits and factors having effects on them would be studied. Also, some of the theoretical models would be reviewed, in which flammability limits would be estimated through experimental data. Finally, with consideration of the aforementioned relations, an optimal method for calculation of upper and lower flammability limits in the gas turbine combustion chamber would be presented.

Within the limitation of this study, reducing the tapering of occlusocervival dimension is the most effective way in increasing resistance form, although, other features were also effective.