Critical Speed Calculation Of Rotor-Bearing System Of Centrifugal Compressor

Stability of centrifugal compressor depends on rotor-bearing system properties. This paper focus on critical speed calculation of rotor-bearing system of centrifugal compressor. The content of this paper including: 1 Moment of inertia calculation of impeller; 2 Stiffness and damping coefficients calculation of tilting pad journal bearing; 3 Critical speed calculation of rotor-bearing system.Both analytic and discrete methods are applied to calculation of impeller moment of inertia. Analytic method is used for cover and hub calculation; discrete method is used for blades calculation. In this way, not only can the result accuracy be guaranteed, but also calculating speed be improved.Tilting pad journal bearing stiffness and damping coefficients calculation is based on Reynolds equation. First, meshing on the pad surface, and working out static pressure distribution of each pad by both finite differences and SOR methods. Second, calculating stiffness and damping coefficients of each pad when it is balanced. Finally, calculating stiffness and damping coefficients of each pad when it is swing by indirect method. Indirect method can reduce Reynolds equation calculating times, expediting calculation speed and reducing error caused by finite differences.Transfer matrix method will be used to calculate critical speed of rotor-bearing system in this paper. Because applying tilting pad journal bearing to rotor, this is a system with damping. As there are eight elements for each state vector, the order of characteristic polynomial is 8n. For example, a system with 40 lumped masses, its order of characteristic polynomial will reach 320. Further more, because there are huge differences between the coefficients of characteristic polynomial, the difficulty of solving this polynomial equation is how to avoid root missing. QR...