No abstract

Power plants operating in combined cycle present higher thermal efficiency (over 60%) and increased power generation when compared to traditional simple cycles, such as gas or steam turbines operating alone. Considering that the power plant evaluated in this paper is already operational, a further development concerning to the power plant control system is required in order to evaluate disturbances and frequency variations, generated by the electrical grid during normal operation, as the loads applied to the turbines are intrinsically associated to the grid frequency. A computer program able to simulate the control system was developed to cope with these instabilities and to guarantee the necessary protection to the power plant operation. The develop program was made using MATLAB Simulink®. The main components of the power plant consists of 2 gas turbines of 90 MW each and a steam turbine of 320 MW, totalizing 500 MW. Firstly, the power plant main components were constructed separately. Once obtained stable models, the exhaust from the gas turbine was connected to the water-steam cycle through the heat recovery steam generator. The main parameters necessary to adjust the model such as gains, limits and constants were obtained from the power plant operational data. The simulation results allowed the evaluation of some key parameters; others are possible but not shown, such as power, exhaust gas temperature, fuel flow and variable stator angles during grid instabilities. The studies were conducted by testing the robustness, response time, transient analysis, steady state analysis and reliability of the proposed model.

This work describes the continuous study that is being done in a small gas turbine that can be used for power generation purposes. Previous studies were conducted aiming to develop a gas generator able to be used in both applications, as a turbojet or as a turboshaft. The gas generator was designed, manufactured and is still under test. The thermodynamic cycle calculation was evaluated as a project-based class, hence, a power turbine was specified and its requirements were determined. The outlet conditions from the gas generator were used to perform the preliminary size of the power turbine. At this phase, the students must use 1D design models considering loss modeling to improve the machine design prediction. The meanline technique was used and the calculations at leading and trailing edges were extrapolated from hub-to-tip, using vortex design methods. With the airfoil stacking for each blade row was possible to determine the 3D geometry of the single stage axial flow turbine. This geometry was assembled in a CAD software to start the mesh generation procedure. After this step, a commercial CFD software was used to calculate the continuity, momentum and energy equations from fluid mechanics. The flow was considered fully turbulent and the two-equation SST turbulence model was set to determine the flow eddy viscosity. The results from preliminary design and 3D techniques were compared and evaluated to complete the first round of the design phase. In this work, experiences from the project-based class on turbomachinery design are described together with the challenges and difficulties that appeared during the project.

Passive wall treatments with circumferential grooves in axial compressors proved to be effective in increasing the compressor stall margin in previous researches by creating a resistance to the flow that leaks in the tip clearance region of the compressor, from the rotor blade pressure side to the suction side. In the present work, a passive wall treatment with circumferential grooves was implemented in a multi-stage axial compressor. Different configurations of circumferential grooves were created at the casing of the first rotor row used in a four-stage axial flow compressor. 3D CFD flow simulations were performed in order to evaluate all the specified configurations aiming to find improvements on compressor stall margin. Investigations on the compressor flow characteristics were realized and the stall margin variations were determined. The numerical simulations were performed based on the Reynolds-Averaged Navier Stokes equations and the turbulence model was the k-ω SST. After the simulations, several rotational speeds of the compressor map characteristics, including the design-point rotational speed, were obtained for the case without casing treatment (smooth wall case) and for the case with circumferential grooves. In the results, passive wall treatment with circumferential grooves demonstrated an improvement in the compressor stall margin, especially for N = 0.60 and N = 0.90 rotational speeds.

Nowadays the environmental and economic aspects emerge as essential alternatives in the design phase of microturbines. In design point definition for micro gas turbine cycles, not only engine performance requirements are necessary to have competitive microturbines but also external requirements, as cost and environmental issues must be in agreement simultaneously. To support engineers in defining the engine design point considering thermodynamic, economic, and environmental aspects, a gas turbine code was developed. The code uses a methodology that includes the sum of microturbine costs as power plant, fuel, and environmental emissions. The developed computer program was written in MATLAB® and is able to simulate the economic and thermodynamic performance of a given micro gas turbine cycle through an optimization process using genetic algorithm. The code is capable of calculating the suitable design point for a specific application. In this work, a 200 kW micro gas turbine recuperated cycle was chosen to study. As initial analysis, a parametric study was made to investigate the behavior of the main decision variables, considering costs and emissions. Afterward, single-objective and multiobjective optimizations were carried out using the objective function according to the proposed methodology. In sequence, a comparison was presented between the design point of a reference available microturbine and the same optimized by the code. The results reveal the importance of the cost optimization, showing how much savings can be achieved in choosing an appropriate design point for microturbines using the methodology implemented in the present work.