Study On Nonlinear Dynamical Characteristics Of Impeller-Rotor With Faults And Lateral Fluid Force

As the most important sub-systems of the turbomachinary, all kinds of faults are often happened in the impeller-rotor system, such as mass eccentricity, cracks in rotating shafts, pedestal looseness, rub-impact fault, and etc. Sometimes these faults can make turbomachines break down. It is necessary to study the nonlinear dynamic characteristics of the impeller-rotor system of the turbomachinary, so that we can understand how those faults arise in theory, and to develop the advanced technology of the fault diagnosis about the turbomachinary.For simplification, some very complicated forces on the turbomachinary are ignored in traditional dynamic models, which are lateral fluid forces. When the impeller-rotor whirls, these foces appear. In fact, lateral fluid forces come from the interaction of the solid body and the fluid in the turbomachine.Based on some outstanding models, a new dynamic model about the rotor system of a turbomachine with all kinds of faults is built in this thesis, taking into accout the lateral fluid forces. The main contents and conclusions of this thesis are:(1) A dynamic model for a rigid rotor of a turbomachinary with both nonlinear lateral fluid forces and nonlinear oil-film force is built, and dimensionless equations of the system are derived. The bifurcation characteristics of the system are studied using numerical integral method, such as bifurcation diagrams, phase trajectory, Poincare maps and etc. The results show that when the rotor is in positive whil, the dynamical characteristics of system become more complicated and there are many chaos and quasi-periodic motion in system because of the effect of the lateral fluid forces. Mass eccentricity of the system makes the motion be complicated.(2) A dynamic model for a cracked impeller-rotor with both nonlinear lateral fluid forces and nonlinear off-film force is built and dimensionless equations of the system are derived. The bifurcation characteristics of the system are studied using numerical integral method, such as bifurcation diagrams, phase trajectory, Poincare maps and etc. The results show that when the rotor is in positive whil, the dynamical characteristics of system become more complicated and there are many chaos and quasi-periodic motion in system because of the effect of the lateral fluid forces. Crack on the rotor makes the motion be complicated, and the complexity of the system's motion state increases as the crack depth increases.(3) A dynamic model for a impeller-rotor with pedestal looseness fault, nonlinear lateral fluid forces and nonlinear oil-fiim force is built and dimensionless equations of the system are derived. The bifurcation characteristics of the system are studied using numerical integral method, such as bifurcation diagrams, phase trajectory, Poincare maps and etc. The results show that when the rotor is in positive whil, the lateral fluid forces make the dynamic characteristics of the system become complicated. As thc mass of the bearing base on loose part of the rotor system, that is m₃, increase, the general shape of the system's bifurcation diagrams change intensively, and the system's motion state change frequently from periodic motion to compound movement.(4) A dynamic model of a impeller-rotor with rub-impact fault, nonlinear lateral fluid forces and nonlinear oil-film force is built and dimensionless equations of the system are derived. The bifurcation characteristics of the system are studied using numerical integral method, such as bifurcation diagrams, phase trajectory, Poincare maps and etc. The results show that when the rotor is in positive whil, the lateral fluid forces arc not the domain reason of making the motion of the system bifurcate if the rotational speed of the rotor is below 980rad/s. When the rotational speed of the rotor exceeds 980rad/s the situation is reverse. Mass eccentricity of the system makes the motion be complicated.(5) A dynamic model of a impeller-rotor with nonlinear lateral fluid forces, nonlinear oil-film force and couple faults of pedestal looseness and rub-impact is built and dimensionless equations of the system are derived. The bifurcation characteristics of the system are studied using numerical integral method, such as bifurcation diagrams, phase trajectory, Poincare maps and etc. The results show that when the rotor is in positive whil, the lateral fluid forces isn't the domain reason of making the motion of the system bifurcate, When the rotational speed of the rotor is below 800rad/s t. When the rotational speed of the rotor exceeds 800rad/s the situation is reverse. Mass eccentricity of the system makes the motion be complicated.(6) A dynamic model of a impeller-rotor with nonlinear lateral fluid forces, nonlinear oil-film forces and and couple faults of pedestal looseness and cracked shaft is built and dimensionless equations of the system are derived. The bifurcation characteristics of the system are studied using numerical integral method, such as bifurcation diagrams, phase trajectory, Poincare maps and etc. The results show that when the rotor is in negetive whil the lateral fluid forces stabilize the system's vibration and play a part of "pamp" in system's motion, when the rotational speed of the rotor is between 800rad/s and 2000rad/s. the variation of the depth don't affect system's bifurcation intensively, when the depth of the crack on the shaft is between 0.3 and 0.7, but the situation is reverse when the depth of the shaft is between 0.7 and 1.0.