抄録
Mixing losses due to cavity related flows in axial steam
turbines contribute considerably to overall aerodynamic losses.
The coherent study presented in this paper examines the
influence of rotor inlet cavity geometry on stage efficiency. The
experimental work is supported by computational analysis. Inlet
cavity geometry has been varied by reducing the axial and radial
cavity lengths along with the volume. Six different configurations
have been examined, focusing mainly on the flow interactions
occurring at the zone between the cavity and main flow and their
impact on stage efficiency. An upper stator-casing platform
prolonged by 17% and 34%, and a radial wall length shortened
by 13% and 25% offered a cavity volume reduction of 14% and
28%, respectively, compared to the initial cavity volume. The
axial cavity wall length reduction impacts drastically on the
vortex formation inside the cavity. A 17% length reduction leads
initially to the bifurcation and re-connection of the vortex during
inflow, whereas the 34% length reduction completely eliminates
the presence of any vortex. On the other hand, the radial cavity
wall length reduction affects the vortex positioning. Generally,
the cases with radial wall length reduction show higher efficiency
relative to the axial cavity length reduction. For the 14% cavity
volume reduction cases this difference rises to 1%, and for the
28% cavity volume reduction the difference is even higher,
attaining a 1.7% efficiency increase.
