Air cooling via evaporation of water droplets injected at the compressor intake duct is the process known as Fogging System, which is among the most used technologies for increasing output power of gas turbines nowadays. The optimal design of this system must consider numerous variables, such as: air temperature (Ta), air relative humidity (RH), duct geometry, amount of water injected (mw), droplets size (Dd), and nozzles location. Since there are so many variables the flow under study is very complicated. In consequence the analytical determination of an optimal Fogging System design is not feasible. In this paper, a numerical model was developed in order to characterize the injection of water at the air intake duct of a Gas Turbine. First, the expressions characterizing the model were included in the CFD software ANSYS CFX v-11 and simulated in a simple geometry (rectangular duct). Validation of CFD results was carried out by comparison with experimental data. Good agreement between numerical results of a control case and experimental data was achieved (deviation < 2%). Then, the influence of key parameters such as: Ta, RH, Dd, mw over the performance of the air cooling system was investigated. Finally, the model was used to design a Fogging System for an existing 120 MW Gas Turbine. For this gas turbine operating under real conditions, the model predicts a net power increment of 2% [7].
A useful methodology in the design of a Turgo Type Turbine (TTT) has been accomplished through the study of a particular three dimensional potential flow, known as Rankine Ovoids. The obtained streamlines solution for this flow was modified implementing several algorithms in order to select a suitable flow profile that could be adapted as a prediction of the flow passing through the buckets of a Turgo runner. Afterwards, the selected profile was incorporated with other geometric parameters, which were based on the hydrodynamic and geometric conditions presented in a TTT, in the design methodology proposed for this investigation. In addition, the equations to calculate power and efficiency of this kind of turbines are included. The global efficiency in the 3DT methodology was reported to be 80.8% for the designed TTT, which it is an expected value for this kind of turbines.
A useful methodology in the design of a Turgo Type Turbine (TTT) has been accomplished through the theoretical calculation of the runner performance and efficiency, using 1D, 2D and 3D theory with certain simpliflying assumptions. The adaptation of several geometric and hydrodynamic parameters into the solution of the Rankine ovoids streamlines function, a three-dimensional potential flow, resulted in the design of a three dimensional TTT runner. A significant CFD simulation of this turbine was achieved, showing its hydrodynamic performance and the behaviour of the streamlines path through the buckets hit by the jet. The distribution of the water volumetric fraction was reported from the nozzle to the buckets In the same way, this numerical approach described the evolution of the velocity vectors from the water crossing the buckets. Furthermore, a comparison between the relative velocity angles from the three dimensional potential theory and the CFD simulation results was done, in order to find potential similarities from the water that actually passes into the buckets.
Our previous work, on development of a design methodology inspired in the analysis of One-Dimensional and Three-dimensional Theories [1], allowed to obtain a Turgo Type Turbine (TTT) bucket using 8 geometric parameters as a function of the jet diameter, and Rankine Ovoids potential flow. CFD models under steady state regime [2] made possible to verify deduced expressions for torque, output power and hydraulic efficiency. In this paper, the effects of the water volumetric fraction distribution in the runner have been included, which are significantly conclusive to understand the runner hydrodynamic behavior and highlighted several optimizations to the performance equations that could be considered as a potential novelty for these turbines. In the same way, an influence study of nozzle parameters determined that the most profitable performance is achieved for an absolute velocity angle coming from the jet of 19.8°. Finally, several differences in the flow distribution in the runner were evaluated through a non-steady state regime CFD simulation, when comparing with the steady state.
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