A mathematical model is developed for the estimation of rotor forward and backward whirl speeds by considering the stationary and rotational dampings. Stationary damping includes external viscous damping in the bearings and rotational damping includes internal viscous and hysteretic damping in the shaft material. The rotors in gas turbines and steam turbines commonly used in military and commercial rotating machines operate at high speeds. These rotors are provided with a set of holes in the shaft to send the coolant to cool the turbine blades. The estimation of the rotor whirl speeds with the above conditions is very difficult. The developed mathematical model predicts the whirl speeds by considering all the above conditions. As the rotor speed increases, the difference between forward whirl and backward whirl increases due to the gyroscopic effect. The study has been done to understand the percentage change in the ratio of forward whirl to backward whirl speed for normal rotor and rotor with above conditions. The whirl speed prediction is done with the combinations of external damping, internal viscous damping and internal hysteretic damping. The more we understand these effects, the more likely we are to make accurate rotating machine diagnoses and to develop appropriate plans for knowledge based maintenance.Cite this Article Ravindra Gardas, Bangarubabu Popuri. Influence of Internal and External Dampings on Shaft Whirl Speeds. Trends in Machine Design. 2016; 3(3): 1–11p.
