Pivot design and angular misalignment effects on tilting pad journal bearing characteristics: Four pads for load on pad configuration
Suh, Junho(Korea Railroad Research Institute)
Nederland | Tribology International
2016-02-25 | 바로가기
Cited by 7
■ View full text
Received 25 February 2016, Revised 26 May 2016, Accepted 31 May 2016, Available online 7 June 2016.
Junho Suha, Yeon-Sun Choib
a Technical Regulation Team, Korea Railroad Research Institute
b School of Mechanical Engineering, Sungkyunkwan University
This paper focuses on angular misalignment between tilting pad journal bearing (TPJB) and spinning journal. Three-dimensional (3D) TPJB numerical model is presented considering the tilt, pitch and yaw motions of the pad, pivot deformation, journal angular motion, and thermo-hydro-dynamic (THD) lubrication model. Cylindrical pivot is assumed to produce only tilting motion with a line contact, whereas the spherical pivot is to provide three angular motions with a point contact. Numerical modeling and simulation results are provided and discussed. Angular misalignment effects on bearing performance are predicted. Spherical pivot design produced invariant characteristics with varying misalignment ratio and phase, whereas the cylindrical pivot showed noticeable variation. Pad yaw and pitch motions led to the differential between the two pivot configurations.
The cylindrical pivot TPJB producing only pad tilt motion and the spherical pivot of tilt, pitch and yaw motions were examined and compared with the varying misalignment ratio and phase. This research can be summarized as follows:
(a) 3D bearing-journal numerical model was provided, where the pad׳s three angular motions, journal angular motion, pivot deformation, thermal distortion and THD lubrication were taken into account. The numerical algorithm for the analysis of the journal-bearing static equilibrium condition was provided.
(b) The equations of motion for the pad tilt, pitch and yaw were presented. Pad self-alignment was achieved with the journal angular motion, which means that the numerical modeling method presented in this research works well. With the varying misalignment ratio and phase, the spherical pivot design produced the invariant static, dynamic and thermal characteristics.
(c) For the evaluation of the force coefficients of the spherical pivot TPJB, two additional terms, perturbing pad pitch and yaw, were considered. These two added terms did not produce any change in the bearing performance being compared to the cylindrical pivot TPJB with the identical input parameters except for the pivot configuration.
(d) Predicted influence of increasing the angular misalignment ratio was examined. The increased misalignment leads to the stiffened bearing in the misalignment direction while the decreased minimum film thickness and the resultant increased lubricant peak temperature were observed.
(e) Pad tilt, pitch and yaw motions were examined with the varying misalignment phase. In the case of the spherical pivot design, pad pitch and yaw angles showed sinusoidal forms whereas the tilt angle stays constant. Tilt angle of the cylindrical pivot also showed the sinusoidal form whose amplitude is less than 5% of the pitch and yaw of the spherical pivot. The maximum pitch and yaw angle coincided with the journal misalignment angle, which means that the pad of the spherical pivot is fully parallel with the shaft׳s angular motion.
(f) Bearing static, dynamic and thermal characteristics with varying misalignment phase and ratio was examined. The angular misalignment stiffened the cylindrical pivot TPJB in the same direction. The lubricant peak temperature was observed on the bottom pad where the most of the bearing load is applied and the resultant decreased minimum film thickness and the heat dissipation occurs.
(g) The angular misalignment in the cylindrical pivot TPJB produced the asymmetric film clearance and pressure distribution in the axial direction. The minimum film thickness drop proportional to the angular misalignment angle was observed in this configuration.
The newly developed 3D TPJB numerical model can be applied to rotordynamic analysis with long rotor simulation where the angular misalignment between spinning journal and bearing easily takes place, and provide accurate predictions of the bearing performance. This research provides a meaningful consideration of the 3D TPJB numerical model and the simulation results employing the pad-journal 3D motion and the new film thickness formula employing the axial variation of the film clearance with pad tilt, pitch and yaw. This study also provides guidance to engineers of rotating machinery for avoiding misalignment induced problems and choosing the optimum pivot design in accordance with the system configurations.
* 관련 자료