Design Calculation and Shaping of the Hydro-Steam Turbine Flow Path with Helical Nozzles

Abstract

Various design versions of the rotor of hydro-steam turbines (HSTs) and their application fields are reviewed. It is shown that the design with nozzles arranged over the periphery has certain shortcomings resulting in a decreased energy efficiency, including a thermodynamically unjustified increase of pressure at the nozzle inlet, which results in excessively high velocities in the nozzle “throat,” a short period of time for which the evaporating medium resides in the nozzle divergent part, and poor aerodynamic characteristics of the peripheral area, which cause increased friction losses during the impeller rotation in a two-phase medium. A hydro-steam turbine impeller design with helical nozzle-channels is proposed. Such design has features that create prerequisites for increasing the turbine efficiency, including a longer time for which the medium resides in the nozzle, a possibility to obtain aerodynamically smooth lateral and peripheral surfaces of the impeller, and better conditions for moisture separation from the medium surrounding the rotating impeller. The conditions under which superheated water enters the impeller are considered, and statements on shaping the impeller profile part are formulated. A procedure for determining the nozzle-channel divergent part’s camber line shape is proposed proceeding from the minimal force interaction between the liquid phase fragments and channel walls. An algorithm for determining the areas of the channel divergent part’s cross sections when the velocity increase and pressure decrease patterns become monotonic in nature as the flow moves from the inlet to the outlet is developed. A solid-state 3D model of the HST four-nozzle impeller obtained in designing the turbine is presented.