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Partial admission in the steam turbine is associated with strong unsteady flow effects on aerodynamic performance. This paper presents a first-of-its-kind computational study of the problem. The unsteady flow field in multiple blade passages and multiple blade rows is governed by the quasi three-dimensional unsteady Navier-Stokes equations, closed by a mixing-length turbulence model. The partial admission is introduced by blocking one segmental arc (or several segmental arcs) of the inlet guide vane of the first stage. The flow equations are solved by using a time-dependent finite volume method.

The calculated unsteady force on rotor blades for a turbine stage at partial admission compares well with the corresponding experimental data. The present results show that a cyclic pumping and sucking phenomenon occurs in the rotor blade row of the first stage, resulting in large unsteady loading and marked mixing …