Three-Dimensional Flow Separations in the Diffuser of a Steam Turbine Control Valve

Abstract

A test rig for Steam Turbine Control Valves is operated at the Laboratory of Turbomachinery of the Helmut-Schmidt-University in Hamburg. The control valve unit containing four independently operable valves is a mockup of a typical steam turbine design converted for the use of compressed air with a maximum of 4 bar. The investigations focus on the transient flow behavior and fluid-structure interaction in connection to valve lift and pressure ratio. Validated by the pressure measurements, transient CFD simulations have been conducted identifying the flow separation structures and the transient behavior of the flow inside the valve throat and diffuser in detail. Similar to published separation structures in compressor cascades the transonic flow inside the valve shows three-dimensional flow separation structures and vortices which can be identified by the two-dimensional streamlines on a plane with a constant and infinitesimal distance to the wall. Furthermore a transient development of these patterns can be identified.