Development of a Software for Rotodynamic Analysis Of Flexible Rotor.

Abstract

Rotating shafts are employed in industrial machines such as steam and gas turbines, cryogenic turbo expanders, turbo generators, internal combustion engines, centrifugal compressors for power transmission. On account of the ever increasing demand for power and high speed transportation, the rotors of these machines are made extremely flexible to allow bending. The shafts of these machines are subjected to torsional and bending vibration and in some cases unstable condition of operation. These machines can develop excessive stress in torsion because of low torsional natural frequencies of the system involving flexible couplings. Determination of natural frequencies and mode shapes is thus important from design point of view. Lateral bending and subsequently whirling of a rotor may arise due to residual unbalance (present due to corrosion, material inhomogeneity etc.) which would cause the simple circular shaft on rigid supports carrying concentrated masses experience synchronous whirl and when the shaft runs at a speed equal to its natural frequency in lateral bending, the whirling becomes predominant. This phenomenon is different from conventional resonance since large amplitude vibration cannot be controlled by additional damping. As the resonance occurs the shaft develops stresses violently, causing the shaft to fail suddenly or decreasing its life. Considering the importance of critical shape and unbalance responses, an effort is made to develop interactive and user-friendly software capable of evaluating the much needed data like critical speed, the associated mode shapes and unbalance-response of a given rotor.