Dynamic Analysis of a Turbocharger Rotor-Bearing System in Transient Operating Regimes
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ORIGINAL CONTRIBUTION
Dynamic Analysis of a Turbocharger Rotor-Bearing System in Transient Operating Regimes Rajasekhara Reddy Mutra1
•
J. Srinivas2
Received: 30 July 2019 / Accepted: 5 June 2020 The Institution of Engineers (India) 2020
Abstract This paper presents a hydrodynamic analysis of the rotor-bearing system of a high-speed turbocharger (TC) rotor supported on the floating ring bearings in transient operating conditions. By considering the temperature-dependent oil-film viscosity of lubricant and film clearances, the pressure distributions and dynamic bearing forces are calculated from the two-dimensional Reynolds equation. The dynamic behavior and stability-related issues are explained while the rotor is in start-up and shut-down conditions. The effects of various parameters including inphase and out-of-phase unbalances at the disks on the dynamics of the overall system are studied. The generalized approach facilitates the user to select the optimum clearances and lubricant type as per the temperature rise in the system. Keywords Finite element (FE) model Transient analysis Temperature-dependent viscosity Floating ring bearings
Introduction A turbocharger is a common platform in several modern automobiles and passenger vehicles. It is used for pressurizing the inlet air at the diffuser end with the help of
& Rajasekhara Reddy Mutra [email protected] 1
Machine Dynamics Lab, School of Mechanical Engineering, Vellore Institute of Technology, Vellore, Tamil Nadu 632014, India
2
Department of Mechanical Engineering, National Institute of Technology, Rourkela, Odisha 769008, India
expanded exhaust gases striking at the turbine end. As these turbocharger rotors are rotating at high speeds, frequent inspections are required to identify the time-to-time developed faults at various locations on the rotor. Bearings, couplings and vanes of compressor and turbine in the assembly are susceptible to several kinds of failures due to abnormal thermal and flow conditions within the casing. Often, semi or full floating ring journal bearings are used to support these high-speed rotors due to their high damping capacity and effective drag forces. Apart from synchronous vibrations occurring from rotor imbalances at low speeds of operation, sub-synchronous oscillations are also generated due to oil whip/whirl instabilities at the bearings [1]. Often the inner and outer bearing film eccentricities around the ring are maintained very low because the outer lubricant film act as a damper for the inner film whirl/whip and vice versa. As the speed increases, the oil whirl/whip instabilities are crossed and the stable-unstable limit cycle behavior is observed. Various types of sub-synchronous oscillations of the system are dictated by the stiffness of the rotor, its inertia, and the bearing parameters. Modeling of the shaft with floating ring bearings has been illustrated with both lumped-parameter [2] and finite element models [3, 4]. Analytical, numerical and approximate techniques were found widely [5–7] to sol
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