Influence of steam extraction slot width on the flow fields of neighboring steam turbine stages

A numerical flow field simulation model for a turbine stage s flow field in front of and next to an extraction slot as well as within the slot itself is presented together with the way of getting solutions. The flow field structures within the extraction slot and in the neighboring stages are depicted for various slot widths, pointing out that steam extraction causes a lasting vortex zone to appear and that the amount of steam extracted, as well as the pressure and velocity distribution along the blade's height of the neighboring stage, all vary with changing slot width. If the amount of extracted steam is kept constant, the dimensions of the lasting vortex zone extend with increasing slot width, while its intensity gets less. If the pressure difference over the extraction nozzle is kept constant, an increase of the slot's width causes the axial thrust and the torsional moment of the preceding turbine stage to increase as well, while reducing the wheel efficiency of both the preceding and the following turbine stage, the flow resistance in the whole extraction tract is being reduced simultaneously.