An Algorithm for Finding Optimum Distribution of the Turbine Blades Considering the Initial Wheel Unbalance

Abstract

Turbine rotor unbalance leads to reduction in performance, wear of the parts and damage. Departure of the mass and center of mass of the blades from their ideal values, manufacturing errors in the wheel and uneven distribution of other parts like shims, are considered as the main sources of unbalance in rotors. Before dynamic balancing of rotor, an optimum distribution of the blades and other parts is needed to be found, such that there remains minimum static unbalance in a stage. To achieve such distribution, the weight moment of the individual blades and other parts are measured in advance. There have been several algorithms in the literature for finding the optimum distribution, however they do not take into account the initial unbalance of the wheel and uneven distribution of the shims. In this paper, a method is proposed to find a distribution of the blades and spacer shims, if any, such that the initial unbalance of the wheel is canceled and the unbalance of the stage is minimized. The results of the proposed method is compared with those obtained from other algorithms and two cases worked out by active companies in this area. The residual unbalances obtained from the proposed method are up to 10 times lower than the minimum values that can be achieved by the other method and, shows an improvement of up to 108 times for the two cases mentioned.

Keywords

• optimum blade distribution
• initial wheel unbalance
• distribution of blades and shims
• heuristic method
• number partitioning