Analysis of turbine performance degradation effects due to geometry variations between actual components and design Intent

Abstract

AbstractThis paper presents a computational analysis regarding the effect of the camber line deformation due to structural errors, on the aerodynamic behavior of a high-pressure steam turbine.In several cases, inaccuracies in the blade geometry can lead to undesirable flow phenomena strongly affecting its overall performance when put in service. The effect of the camber line deformation on the performance of an experimental axial steam turbine is investigated hereafter. A high fidelity inspection of the actual geometry of both a stator and a rotor blades randomly chosen among the similar blades of the same row has been carried out, using a 3D co-ordinate measurement machine. The cross sections of the blades obtained by the measurement were compared with those produced by the design process to evaluate the change in blade inlet/exit angles. The actual (measured) model has been used as input into a streamline curvature solver to evaluate its overall performance assuming a uniform distribution of the geometrical error across the blades of the same blade row, the loss generation mechanisms within the flow field have been further investigated and analysed using a high fidelity 3D Navier-Stokes solver.A measurable change of efficiency as well as in the total power delivered by the turbine was found. This suggests that the accumulated error caused during the manufacturing procedure plays a significant role in the overall performance of the machine by making it less efficient by almost 1% due to the intensification of the hub and casing secondary flows, as well as to the thicker boundary layers on the blade surfaces revealed by the numerical prediction of the flow.