Numerical analysis of adaptive control in LP turbines

A new design idea of adaptive control in LP steam turbines under conditions of (1) extraction of steam to the extraction point and (2) seasonal changes of pressure in the condenser is discussed. Nozzle blades of a stage located directly downstream of the extraction point or of the exit stage located upstream of the exit diffuser have adjustable trailing edges that can adapt the geometry of the blading system to the changing flow conditions. The idea has been validated numerically on a group of two exit stages of a 60MW extraction/condensation turbine. A series of flow calculations have been performed using a FlowER code for solving the flow of compressible viscous gas in a 3D turbomachinery environment. As a result, characteristics of the design, including the mass flow rate, flow angles in characteristic sections, enthalpy losses and turbine power, have been obtained in a range of given pressure drops and nozzle blade stagger angles. Based on these characteristics, the adequate position of the nozzle blade has been found to adapt the stage (stage group) geometry to the changing flow conditions. The advantages of adaptive control in the form of increased turbine efficiency and power have also been estimated.