Off-design flow analysis and performance prediction of axial turbines

Abstract

Through-flow methods for calculations in axial flow turbines are limited by two facts: They cannot handle local flow reversal, and loss prediction at off-design operating conditions is not sufficiently accurate. An attempt to overcome these limitations is presented in this paper. The developed calculation method is based on the through-flow theory and the finite element solution procedure, but it also includes extensions and improvements. Consequently, the method may be used to predict the flow field and the turbine performance at the design load as well as for wide range of part loads. The code is able to calculate flow in axial turbines at subsonic and transonic conditions. The reliability of the method is verified by calculations for several gas and steam turbines. Results of flow calculation and performance prediction of 4-stage experimental air turbine and LP steam turbine are also presented herein. Low load operation with flow reversal in the hub region behind the last rotor blade row and loads, at which part of blading operates with power consumption, are especially analyzed. All numerical results are compared to the results of extensive experimental investigations. The correspondence, even for low loads, is very good.