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초임계 CO<sub>2</sub> 발전용 파워 터빈의 회전체 동역학 해석 및 구동 시험
이동현,김병옥,선경호,임형수,Lee, Donghyun,Kim, Byungok,Sun, Kyungho,Lim, Hyungsoo 한국트라이볼로지학회 2017 한국윤활학회지(윤활학회지) Vol.33 No.1
This paper presents a rotordynamic analysis and the operation of a power turbine applied to a 250 kW super-critical $CO_2$ cycle. The power turbine consists of a turbine wheel and a shaft supported by two fluid film bearings. We use a tilting pad bearing for the power turbine owing to the high speed operation, and employ copper backing pads to improve the thermal management of the bearing. We conduct a rotordynamic analysis based on the design parameters of the power turbine. The dynamic coefficients of the tilting pad bearings were calculated based on the iso-thermal lubrication theory and turbine wheel was modeled as equivalent inertia. The predicted Cambell diagram showed that there are two critical speeds, namely the conical and bending critical speeds under the rated speed. However, the unbalance response prediction showed that vibration levels are controlled within 10 mm for all speed ranges owing to the high damping ratio of the modes. Additionally, the predicted logarithmic decrement indicates that there is no unstable mode. The power turbine uses compressed air at a temperature of $250^{\circ}C$ in its operation, and we monitor the shaft vibration and temperature of the lubricant during the test. In the steady state, we record a temperature rise of $40^{\circ}C$ between the inlet and outlet lubricant and the measured shaft vibration shows good agreement with the prediction.
터빈 시뮬레이터용 틸팅패드 저널베어링의 열윤활 해석 및 패드 온도 측정
이동현(Donghyun Lee),선경호(Kyungho Sun) 한국트라이볼로지학회 2017 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.33 No.3
Tilting pad journal bearings(TPJBs) are widely used for high speed rotating machinery owing to their rotordynamic stability and thermal management feature. With increase in the rotating speed of such machinery, an increasingly important aspect of TPJB design is the prediction of their thermal behaviors. Researchers have conducted detailed investigations in the last two decades, which provided design tools for the TPJBs. Based on these previous studies, this paper presents a thermohydrodynamic(THD) analysis model for TPJBs. To calculate pressure distribution, we solve the generalized Reynolds equation and to predict the lubricant temperature, we solve the 3D energy equation. We employ the oil mixing theory to calculate pad inlet temperature; further, to consider heat conduction via the pad, we solve the heat conduction equation for the pads. We assume the shaft temperature as the averaged oil film temperature and apply natural convection boundary conditions to the pad side and back surfaces. To validate the analysis model, we compare the predicted pad temperatures with those from previous research. The results show good agreement with previous research. In addition, we conduct parametric studies on a TPJB which was used in a gas turbine simulator system. The predicted results show that film temperature largely depends on the rotating speed and oil supply condition.
표면이 마모된 틸팅 패드 저널베어링의 열윤활 해석 및 온도 측정
이동현(Donghyun Lee),선경호(Kyungho Sun),김병옥(Byungock Kim),강동혁(Donghyuk Kang) 한국트라이볼로지학회 2017 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.33 No.4
With the increase in adoption of tilting pad journal bearings (TPJBs), various failure mechanisms related to TPJBs have been reported, of which pad wear is a frequently reported one. Pad wear causes change in geometry of the bearing, which can sometimes result in the failure of the entire system. The objective of this research is to investigate the influence of pad wear on the pad temperature, which is one of the widely used condition monitoring methods for TPJBs. For the theoretical investigation, thermohydrodynamic (THD) analysis was conducted by solving the generalized Reynolds equation and the 3D energy equation. The results of the analysis show that the temperature of the loaded pad increases while that of the unloaded pad decreases, when there is wear on the loaded pads. In addition, the minimum film thickness decreases with an increase in the wear depth. A validation test was conducted with a test rig, which mimics the axial turbine when a test rotor is supported by two TPJBs. The test bearing consists of five pads with a diameter of 60 mm, and a resistance temperature detector (RTD) is installed in the pad for temperature monitoring. The test was performed by replacing the two loaded pads with the worn pad. The test result for the TPJB with wear depth of 30 μm show that the temperatures of the loaded pads are 8 °C higher and that of the unloaded pad is 2.5 °C lower than that of the normal TPJB. In addition, the predicted pad temperature shows good agreement with the measured pad temperatures.
이동현(Donghyun Lee),김병옥(Byungok Kim),선경호(Kyungho Sun) 한국트라이볼로지학회 2018 한국윤활학회지(윤활학회지) Vol.34 No.5
A multi-stage compressor (MSC) is comprised of several impellers installed in the pinion gear shaft driven by a main bull gear. In the pinion shaft, a thrust collar (TC) is installed to support the thrust load. The TC makes the lubrication system simpler in the MSC; therefore, it is widely used in similar kinds of machinery. Typically, TCs are installed on both sides of the bull gear and pressure is developed in the lubricated area by creating a taper angle on the TC and bull gear surface. In the current study, we developed a numerical analysis model to evaluate the performance of the TC considering its design parameters. We sloved the Reynolds equation using the finite element method and applied the half Sommerfeld condition to consider cavitation. Based on the pressure calculated in the lubricated area, we calculated the power loss and minimum film thickness. In addition, we calculated stiffness and damping using perturbation method. We performed parametric studies using the developed model. The results of the analysis show that the maximum pressure presents in the center area of the TC and it increases with the taper angle. The area over which pressure is developed decreases with the taper angle. The results also show that there is an optimum taper angle providing minimum power loss and maximum film thickness. Additionally, the stiffness and damping decrease with the taper angle. As the applied load increases, the power loss increases and the minimum film thickness decreases. However, the stiffness and damping increase with the applied load.
초임계 CO₂ 발전용 파워 터빈의 회전체 동역학 해석 및 구동 시험
이동현(Donghyun Lee),김병옥(Byungok Kim),선경호(Kyungho Sun),임형수(Hyungsoo Lim) 한국트라이볼로지학회 2017 한국윤활학회지(윤활학회지) Vol.33 No.1
This paper presents a rotordynamic analysis and the operation of a power turbine applied to a 250 kW super-critical CO₂ cycle. The power turbine consists of a turbine wheel and a shaft supported by two fluid film bearings. We use a tilting pad bearing for the power turbine owing to the high speed operation, and employ copper backing pads to improve the thermal management of the bearing. We conduct a rotordynamic analysis based on the design parameters of the power turbine. The dynamic coefficients of the tilting pad bearings were calculated based on the iso-thermal lubrication theory and turbine wheel was modeled as equivalent inertia. The predicted Cambell diagram showed that there are two critical speeds, namely the conical and bending critical speeds under the rated speed. However, the unbalance response prediction showed that vibration levels are controlled within 10 mm for all speed ranges owing to the high damping ratio of the modes. Additionally, the predicted logarithmic decrement indicates that there is no unstable mode. The power turbine uses compressed air at a temperature of 250°C in its operation, and we monitor the shaft vibration and temperature of the lubricant during the test. In the steady state, we record a temperature rise of 40°C between the inlet and outlet lubricant and the measured shaft vibration shows good agreement with the prediction.