Parametric Study of Flexure Pivot Bearing Induced Thermal Bow-Rotor Instability (Morton effect)

This paper investigates the journal asymmetric temperature induced thermal bow vibration of a rotor, as supported by a flexure pivot journal bearing (FPJB). Thermal bow induced vibration, known as Morton effect (ME) is caused by non-uniform viscous heating of the journal, and the resulting thermal bow often causes increasing vibration amplitudes with time-varying phase. Full FJPB's structural and thermal finite element models are developed and integrated into the flexible rotor model. The model is validated by comparing its predicted ME response with experimental results. A FPJB model, which uses predicted “equivalent” radial and tilting stiffness of the bearing is compared with the full FEM-based model. The impact of FPJB's design parameters such as web thickness, bearing material, and housing thicknesses are investigated with parametric studies. The results show that FPJB parameter values may have a major effect on the speed range of ME vibration, and its severity.

Tilt Pad Bearing Distributed Pad Inlet Temperature with Machine Learning -Part I: Static and Dynamic Characteristics

Uncertainty in mixing coefficients MC for estimating pad leading edge film temperature in tilt pad journal bearings, reduces the reliability of predicted characteristics. A 3D Hybrid Between Pad (HBP) model, utilizing CFD and machine learning ML, is developed to provide the radial and axial temperature distributions at the leading-edge. This provides a ML derived, 2D film temperature distribution in place of a single uniform temperature. This has a significant influence on predicted journal temperature, dynamic coefficients, and Morton Effect response. An innovative Finite-Volume-Method (FVM) solver significantly increases computational speed, while maintaining comparable accuracy with CFD. Part I provides methodology and simulation results for static and dynamic characteristics, while Part II applies this to Morton Effect response.

Tilt Pad Bearing Distributed Pad Inlet Temperature with Machine Learning -Part II: Morton Effect

The Morton Effect (ME) occurs when a bearing journal experiences asymmetric heating due to synchronous vibration, resulting in thermal bowing of the shaft and increasing vibration. An accurate prediction of the journal's asymmetric temperature distribution is critical for reliable ME simulation. This distribution is strongly influenced by the film thermal boundary condition at the pad inlets. Part I utilizes machine learning ML to obtain a 2D radial and axial distribution of temperatures over the leading edge film cross section. The hybrid finite volume method FVM – bulk flow method of Part I eliminated film temperature discontinuities, and is utilized in Part II for improving accuracy and efficiency of ME simulation.

Squeeze Film Damper Suppression of Thermal Bow-Morton Effect Instability

The Morton effect (ME) is a synchronous vibration problem in turbomachinery caused by the nonuniform viscous heating around the journal circumference, and its resultant thermal bow (TB) and ensuing synchronous vibration. This paper treats the unconventional application of the SFD for the mitigation of ME-induced vibration. Installing a properly designed squeeze film damper (SFD) may change the rotor's critical speed location, damping, and deflection shape, and thereby suppress the vibration caused by the ME. The effectiveness of the SFD on suppressing the ME is tested via linear and nonlinear simulation studies employing a three-dimensional (3D) thermohydrodynamic (THD) tilting pad journal bearing (TJPB), and a flexible, Euler beam rotor model. The example rotor model is for a compressor that experimentally exhibited an unacceptable vibration level along with significant journal differential heating near 8000 rpm. The SFD model includes fluid inertia and is installed on the nondrive end bearing location where the asymmetric viscous heating of the journal is highest. The influence of SFD cage stiffness is evaluated.

Squeeze Film Damper Suppression of Thermal Bow: Morton Effect Instability

The Morton Effect (ME) is a synchronous vibration problem in turbomachinery caused by the non-uniform viscous heating around the journal circumference, and its resultant thermal bow and ensuing synchronous vibration. This paper treats the unconventional application of the SFD for the mitigation of ME-induced vibration. Installing a properly designed squeeze film damper (SFD) may change the rotor’s critical speed location, damping and deflection shape, and thereby suppress the vibration caused by the ME. The effectiveness of the SFD on suppressing the ME is tested via linear and nonlinear simulation studies employing a 3D thermo-hydrodynamic (THD) tilting pad journal bearing, and a flexible, Euler beam rotor model. The example rotor model is for a compressor that experimentally exhibited an unacceptable vibration level along with significant journal differential heating near 8,000 rpm. The SFD model includes fluid inertia and is installed on the non-drive end bearing location where the asymmetric viscous heating of the journal is highest. The influence of SFD cage stiffness is evaluated.

Experimental Study of Cyclic Synchronous Vibration of an Integrally Geared Centrifugal Compressor for Air Separation Application

This paper presents an experimental study of high cyclic synchronous vibration observed on the top pinion of an integrally geared centrifugal compressor. This cyclic synchronous vibration was different from the previously reported Morton effect. In a typical cycle, the vibration began with a long quiet period, then took off and followed by settle-down. Sometimes, vibration peaked above a shutdown limit, which subsequently tripped the compressor and then the air separation plant. Frequency spectra showed this new cyclic vibration was dominated by synchronous vibration. To obtain reliable and meaningful phase information for the diagnosis, a new signal processing technique was developed to analyze the historic vibration data captured without a key phasor. An experimental study of this new rotordynamic phenomenon was conducted on the machine in operation. Test data showed the high cyclic synchronous vibration was closely related to Morton effect though it does not have a significant phase shift. An effective remedy measure was therefore taken, and the cyclic synchronous vibration was eliminated. Since then, this compressor has been running smoothly for 17 months. A possible mechanism of the cyclic vibration is discussed in this paper.

Stability Analysis of the Morton Effect of Rigid and Flexible Rotors

This paper presents a stability analysis of the Morton effect. The analysis is an extension of the Murphy and Lorenz method [11] and is based on better estimates of three influence coefficients linking the phenomena contributing to the Morton effect: the total response to the rotor unbalance, the temperature difference on the rotor surface induced by synchronous vibrations and the thermomechanical deformation of the rotor. The models used in the present work are more complex and accurate because they are based on the non-linear unbalance response (large amplitude vibrations) of the rotor, on the non-isothermal analysis of the journal bearing flow and on a three-dimensional thermos-elastic analysis of the rotor. The results obtained with the original stability analysis of Murphy and Lorenz and with the modified one are compared with original experimental data obtained for a short (rigid) and long (flexible) rotor guided by a ball bearing and by a cylindrical bearing and presented in a previous work [20]. Both methods confirm the experimental results obtained for a short (rigid) rotor. They show that this rotor is not subject to instabilities generated by the Morton effect. However, the results obtained for a long (flexible) rotor are different. The simplified method of Murphy and Lorenz shows a stable behavior while the modified method presented in this work confirms the findings of [20] and indicates that the rotor could be subject to a Morton effect at rotational speeds close to the experimental conditions. The improvements obtained by using the modified stability analysis are therefore clearly underlined, as well as its inherent limitations.