FLUENT模拟齿轮转动

Journal of applied science in the thermodynamics and fluid mechanics Vol. 1, No. 1/2007, ISSN 1802-9388
NUMERICAL SIMULATIONS OF UNSTEADY OIL FLOWS IN THE GEAR-BOXES
Frantisek LEMFELD*, Karel FRAŇA**, Jiří UNGER*** *Technical University of Liberec, Department of Power Engineering Equipment Studenstká 2, 46117, Liberec 1, Czech Republic Phone: (+ 420)485353434, Fax: + 420485353644, E-mail: frantisek.lemfeld@email.cz **Technical University of Liberec, Department of Power Engineering Equipment Studenstká 2, 46117, Liberec 1, Czech Republic Phone: + 420485353436, Fax: + 420485353644, E-mail: karel.frana@seznam.cz ***Technical University of Liberec, Department of Power Engineering Equipment Studenstská 2, 46117, Liberec 1, Czech Republic Phone: + 420485353405, Fax: + 420485353644, E-mail: jiri.unger@tul.cz This paper deals with the behavior of oil in the gear-box. For numerical simulations, the commercial software Fluent was used for relatively complicated problems of the two-phase unsteady turbulent flow. First of all, problems are focused on simplified models of one gear and set of gears, then finally on the model of complete gear-box. These cases are solved as unsteady problem - computation leads from start time, where oil pool is in calm, to the stable regime, where oil pool is in balance.The numerical study is consisted of several cases; run-up cogwhell or set of gears with the calm pool of oil, run-up with changes of oil pool sway, influence of viscosity changes on oil flows inside gear-box and run-up complete gear-box with calm pool of oil. Keywords: numerical simulation, oil flows, multiphase flow, gear-box

t = 0.5 s
t=1s
t=2s
t=5s
Figure 4a to 4d : Time procedure for single gear
As we can see from mentioned figures, run-up of cogwheel has influence to splashing of oil around gear-box. Initial amplitude of oil pool, caused by start, becomes stable after time as a splashing himself. In time t = 5 s doesn't happen any changes in the flow and we can say that this state we can call the steady state flow. 3.2 Set of gears – the calm pool of the oil After simulation of single gear, the set of gears was considered. Because mathematically modeled roughness do not involved influence of ejecting oil in place of cogwheels interaction, approximate volume flux of oil was calculated and the distance of cogwheels was modified to fit with this calculation. During computation was necessary to use lower value of the time step then in case of single gear. Following figures show progression of oil flow from start state to stable state of flow (Fig.5a to Fig.5d).
1INTRODUCTION The subject of this study is a numerical simulation of incompressible unsteady oil flows in gear-boxes [4]. First of all this common technical problem involves removal of heat from gear set. Heat is generated on the surface of gears in consequence of mutual friction meshing cogs. The cooling is done by the oil film which simultaneously decreases friction effect on the surface of the gear. Lubrication is solved by the waiding one of the gears in oil bath. Insufficient removal of heat leads to increasing temperature in the oil bath with changing material properties of oil. This leads to decreasing capability reduce friction. The increasing friction increases heat and backward effect is change of temperature in oil bath. Throwing of oil from the wading gear could be used for lubrication of bearings by force of intake area placed in the top of the gear-box. The problem is composed by the oil and surrounding air. These two components create two-phased system. Numerical simulation is performed by the commercial software Fluent. First of all, problems are studied on the simplified model of one gear with spiral gearing. The gear wades with the constant surface speed in the oil pool and effect of changing separate parameters with influence on behavior of the two-phased compound oil-air is observed. In the next step set of gears is involved into calculation. Set of gear is composed from main gear, which wades again in the oil pool with the constant speed and from the second gear, which serves to transmition torque and has no contact to the oil pool. Finally, the complete model of the gear-box is presented. 2 SOLVING METHOD Because reflect real cogs is relatively difficult for the solution, general influence of gearing is replaced by modeling roughness height, which corresponds to height of real cogs. The numerical simulation is realized by the Finite Volume Method (FLUENT) [1]. Implicit scheme for the time discretization is supposed. Twophased model (oil-air) is solved by Volume of Fluid (VOF) model with scheme Geo Reconstruct [2]. For cases of turbulent flows the statistic RANS model k-ω Standard is used [3]. Boundary conditions for all geometry in model are set to be „wall“ [4,7]. Parameters such as rotation movement and roughness height