<p>Nowadays, the ever-increasing world electricity generation by renewable energy sources has brought about changes in conventional power plants, such as large steam turbines, which were used to contribute widely to meet the world’s energy needs by operating mostly at fixed conditions. Now, instead, they have to be capable to operate with greater flexibility, including rapid load changes and quick starts as well, in order to make the most of the renewable resources while guaranteeing the coverage of any shortcomings of the latter with traditional fossil fuel systems. Such service conditions are particularly challenging for the exhaust hoods, which have a great influence on the overall turbine performance, especially at off-design conditions, converting the residual kinetic energy leaving the last stage turbine blades into static pressure. In fact, the complex and high rotational 3D flow generated within the diffuser and the exhaust hood outer casing can cause an increase in aerodynamic losses along with the detriment of the hood recovery performance. For these reasons, an optimized design and adequate prediction of the exhaust hood performance under all the machine operating conditions is mandatory. Since it has been widely proven that the exhaust hood flow structure strongly interacts with the turbine rear stage, the necessity to discretize it as well becomes crucial, requiring a remarkable computational effort, especially for full unsteady simulations. Even if adopting simplified approaches to model the last stage and exhaust hood interfaces, such as the so-called Frozen Rotor and the Mixing Plane ones, helps to keep the computational cost low, it can be not enough to optimize the exhaust hood design, since a significant number of CFD simulations are required in order to identify the most performing geometry configuration. For these reasons, a simplified model of the exhaust hood must be adopted to analyze all the possible design variants within a feasible time.</p><p>The purpose of this work is to present a strategy for the exhaust hood design optimization through a Design of Experiment analysis by using CFD simulations. Hence, a parametric model has been developed as a function of key geometrical parameters of both the exhaust hood and the diffuser, taking into account the strong fluid-dynamic coupling between the two components. A periodic approximation was introduced in the modeling, making it possible to raise the number of the geometrical parameters of the DOE, while keeping the computational effort low. A response surface has been achieved as a function of all the key geometrical parameters, allowing to identify the region of maximum pressure recovery coefficient, which has been also investigated by using a full 3D model, to demonstrate the effectiveness of the procedure here presented.</p>

Development of a Design Approach for the Optimization of Steam Turbine Exhaust System Performance Through Cfd Modelling

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

Turbo Expo 2021

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