Abstract
The performance simulation of an axial turbine is achieved in a simple way from the calculation of velocity diagrams. For this purpose, a reliable loss model is needed for the flow through each stationary or rotating axial blade cascade. A loss coefficient assessment is conducted through the establishment of a correlation between the maximum profile velocity ratio and a circulation parameter, dedicated specifically to turbine cascades. A detailed examination of published wind tunnel cascade tests available in the literature provides enough experimental data to support the proposed correlation. Afterwards, the surface diffusion is quantified and the total pressure loss estimation is obtained from the boundary layer momentum thickness and conservation equations for the downstream flow. Further validation of the proposed loss model is presented from published experimental results in turbine cascades and stages. The simulation methodology is also demonstrated in two single-stage steam turbine units applied to the oil refining industry, in comparison with performance factory tests results.
Highlights
Modern turbomachinery design practice counts on CFD techniques to develop three-dimensional blade sections, simple methods with an empirical basis are still needed for the mean-line design
The inlet to exit cascade density ratio will depend on the velocities, as given by the aero-thermal relations, making the velocity diagram problem an intricately coupled system of equations that need to be solved by an iterative procedure
A loss model for the mean-line flow through an axial turbine stage is proposed in this work, based on the works of Baljé [11] and Stewart et al [14]
Summary
Modern turbomachinery design practice counts on CFD techniques to develop three-dimensional blade sections, simple methods with an empirical basis are still needed for the mean-line design This preliminary design phase is the starting point and should provide a solid foundation for the final design, or else adding more complex flow analysis techniques would not contribute to a good result [1]. The axial turbine performance simulation at a preliminary design phase is traditionally achieved from the determination of flow velocity diagrams This task involves the use of aero-thermal relations as well the assessment of a flow loss model. The inlet to exit cascade density ratio will depend on the velocities, as given by the aero-thermal relations, making the velocity diagram problem an intricately coupled system of equations that need to be solved by an iterative procedure
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