Fluid- and structural mechanical study of the inflow of a steam turbine

This work presents design guidelines for two categorically different concepts of a power plant turbine inlet duct; a ring-type inlet chamber and an inlet scroll. Subjects of the analysis are aerodynamic considerations of the flow field in the ducts as well as the impact of the chamber topology on the radial clearances influencing casing deformations in stationary and transient load cases. To show the reliability of the CFD-program used, calculated results are compared with measured data. The numerical method catches the main physical effects observed in the reference cases with high accuracy. The flow field in the ring-type inlet chamber strongly depends on the Reynolds number Re; according to Re a symmetrical or swirling flow field can be observed. The calculations indicate that measured values in test stands of inlet ducts with a Reynolds number that is not comparable to the full-size model should be examined carefully. The optimization of the ring-type inlet chamber leads to a geometry with minimum losses from an aerodynamic and mechanical point of view. The greatest benefit can be realized by an optimized flow into the downstream following stator blades. The analysis of the inlet scroll unveils a negative influence of eccentrically arranged pipe ends on the leakage losses. For the casings investigated a very compact design leads to minimum total losses. When choosing the scroll topology, the leakage losses should be minded, as the link between scroll size and casing deformation is not negligible. A comparison of both optimized inlet chambers shows that they have the same loss level. The selection of one concept should take into account stress distributions and the offsets of casing flanges including their consequences.