Comparison of the Effectiveness of Using Adjustable (Turning) Nozzle Vanes in Turbine Stages of Different Types

The high efficiency of turbine stages with adjustable (turning) nozzle vanes (ANV) is determined in many respects by the possibility of achieving the minimum permissible clearance between the tips of the turning nozzle vanes and the fixed root and peripheral meridional outlines and maintaining it when turning the blades, since the working fluid flow-over through the clearances is the main source of losses. The requirement for ensuring the minimal size and intactness of clearances in the turning nozzle vane systems is possible through the use of various types of turbine stages - axial, radial, radial-axial with impulse- or reaction-type blading of the blade rows. In so doing, it is necessary to take into account the level of complexity and cost of manufacturing the stage of a particular type. The article presents the results of a computational (in the ANSYS CFX environment) study of the influence of variable working fluid flowrates on the relative internal efficiency for four turbine stage versions: an axial impulse-type stage (AI-S); a radial-axial stage (RAS); a stage with radial nozzle vanes (RNV), a annular bladeless radial-axial channel (ARAC) and axial blade row (ABR); and an axial reaction-type stage (AR-S). The calculations have been carried out over a wide variation range of rotation speed and flowrate (0.5 < Gi/G0 < 1.5). The influence of individual loss components on the efficiency hoi has been analyzed in detail. The highest values of efficiency hoi over the entire working fluid flowrate variation range have been obtained for the radial-axial stage (RAS).