EFFECTS OF TURBULENCE ON DYNAMIC PERFORMANCE OF ACCELERATED/DECELERATED HYDRODYNAMIC JOURNAL BEARING SYSTEM

Abstract

The hydrodynamic journal bearing system has found wide -spread application :in high speed rotating machines such as compressors, gas turbines, water turbines, steam turbines, alternators, air-chart etc. As rotors generally operate at high speed,. the lubricant flow in the clearance space of journal bearing doesn't remain laminar and for accelerated! decelerated journals the threshold speed of instability`is crossed from both side. Therefore, there is still a need to sutdy.the dynamic response of the hydrodynamic journal bearing system considering superlaminar flow. In this thesis, the analysis have been done for the fluid-flow-field in the clearance space of plane circular hydrodynamic journal bearing system, using short bearing analysis, because short bearing approximation gives more economical solutions. The analysis is carried out for the case of short bearings (LID <0.5)under laminar, transition and turbulent flow conditions,assuming the perfectly rigid journal and bearing. Modified Reynolds equation is used to examine above three flow regimes. The positive pressure zone is establised after deleting subambient pressure around clearance space. Linear and non linear motion trajectories at constant speed have been obtained using the fourth order Runge-Kutta method. The non linear motion trajectories during acceleration and deceleration is also obtained. Journal centre trajectories at constant speed and laminar flow show the expected trend i.e. system is stable below threshold speed curve, unstable above it and makes a limit cycle at the conditions on the curve. But for superlaminar flow stable behaviour is found at some distance away from the stability curve and journal makes limit cycle of decreasing magnitude between this stable point and point on threshold curve. The behaviour during stopping/starting of Journal centre trajectories obtained. from nonlinear