Abstract
Abstract The article discusses the phenomenon of stator Wake/Rotor cascade (W/R) interaction in a steam turbine stage, and the ability to capture it in turbine stage design calculations making use of standard numerical codes. Firstly, the W/R interaction is analysed by comparing its real, experimentally recorded course with the numerical results obtained using vortex theory models and methods. This part of the analysis ends with formulating a conclusion about stochastic nature of the W/R interaction and indicating its reason, which is the vortex structure of the stator wake. Next, a question is discussed whether and how this stochastic nature of the examined phenomenon can be taken into account in calculations of Reynolds Averaged Navier-Stokes (RANS) equations. Differences are indicated between the uniform pattern of the stator wake obtained using a RANS code and the vortex structure of the real wake. It is concluded, however, that despite these differences the RANS results correctly reflect the time-averaged course of the real W/R interaction, and the process of averaging the flow parameters on the sliding plane between stator and rotor calculation areas can be treated as sort of “numerical averaging” of different realisations of the W/R interaction.
Highlights
The article discusses the phenomenon of stator Wake/Rotor cascade (W/R) interaction in a steam turbine stage, and the ability to capture it in turbine stage design calculations making use of standard numerical codes
The analysis described in the previous sections delivers a relatively clear and consistent pattern of the W/R interaction as an unsteady process controlled by the initial distribution of stator wake vortices at the time when the wake is cut apart by the rotor blades
The article discusses the interaction between the stator wakes and the rotor cascade in a turbine stage
Summary
Steam turbines are widely used in shipbuilding industry as the main engines on ships which need huge driving power (large super-tankers, for instance), or the nature of their operation is characteristic for long-distance sailing without calling at a harbour (ice-breakers or marine submarines with nuclear propulsion systems). That is why steam turbine designers attempt to calculate basic turbine parameters very accurately, taking into account as many factors as possible One of these factors which were given special attention in recent years is the effect of interaction of the secondary vortices forming in turbine blade stator and rotor passages on the level of the generated stage loss. The abovementioned vortex interaction in a steam turbine stage can be successfully analysed using Computational Fluid Dynamics (CFD) codes which solve the Reynolds Averaged Navier-Stokes (RANS) equations in computational domains of arbitrary geometry It should be stressed, that these CFD calculations require extremely fine grids to take into account the widest possible range of small-scale vortices. The conclusions resulting from the presented analysis are valid for both inland and marine applications of steam turbines
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