Numerical Analysis of T353 Steam Turbine to Investigate the Effect of Unbalance Masses on Harmonic and Transient Cases

Abstract

The study of the rotor-bearing system is always regarded the rotary structures, and it is important to take in considerations the motion characteristics; the numerical representation of T353 steam turbine, which is working as a drive to many pumps in Daura Refinery, has been taken and described the flexibility for this rotor turbine with transient and harmonic cases with the variation of the unbalance masses, the analysis has been done numerically as finite element analysis by using ANSYS, this paper shows that the selection of beam element type BEAM188 for the rotor shaft and element type COMBI 214 for journal bearings for both sides  are best representation getting good agreement. The calculations of the coefficients of stiffness and damping because of oil film in horizontal, vertical and cross directions has been done and their variations with rotation speed, eccentricity, and Sommerfield number by MATLAB, The turbine's critical speed has been determined. by Campbell diagram, it is a speed at which the response will be maximum hence, its called the resonance case, the variation of unbalance masses with speeds of turbine has been studied with obtaining the maximum response for each case, then the system stability has been investigated and found the stability line which gives a clear results, so if rotation lies up or under this line, the system will be stable, but if the turbine speed locates on the line, it mean we have a resonance case and it will be unstable case, that will help engineers to know the dynamic characteristics of the system furthermore, could know the critical speed and the effect of increasing the unbalance mass on the response and the system stability.