Steam turbines are applied in production plants characterized by very large injections of low pressure steam. For this reason the design and optimization of the injection section is fundamental to obtain an adequate level of turbine efficiency and ensure uniform flow at the inlet of the low pressure stages downstream the injection.
This paper illustrate the optimization performed on a Steam Turbine injection system for a unit in which injection flow is 80% of the total outlet mass flow. Optimization was performed varying the shape of the original steam guide with the twofold objective of minimizing the total pressure loss and uniform the circumferential flow distribution.
The analysis has been performed using RANS 2D and 3D CFD solver. The design process has been structured in 3 different steps: i) Axisymmetric CFD screening based on DOE ii) 3D-CFD verification of the profile shape previously obtained with the additional estimation of the flow uniformity on 360° iii) 3D-CFD of the injection module including the reaction stage upstream and the first LP stage downstream, with the stator modeled on 360°.
The main outcomes are presented in terms of total pressure loss and uniformity of circumferential flow, both strongly reduced with respect to the original design. Moreover in order to characterize the excitation associated with flow non-uniformity an analysis in the frequency domain of the flow distribution has been performed.