Analysis Of Flow Field And Numerical Study Of Seal Structure For High-Speed Gearbox

High-speed driving gearbox is one of the key components of the power bogie. With the improvement of train speed, the pressure distribution within the driving system and the system temperature change become more complicated, which asks for a higher sealing performance for gearbox. Sealing performance will directly affect its operational reliability as well as gear and bearing service life. In this paper, taking the high-speed driving gearbox as the research object, the distribution of the flow field within the gearbox and the lubrication system seal cavity were analyzed, providing theoretical guidance for the design of the gearbox lubrication and sealing system.Basing on the incompressible fluid control equations and the RNG k-ε turbulence model, the two-dimensional simulation model of the flow field within the high-speed EMU driving gearbox was set up. The Navier-Stokes equation and energy equation were discretized with the finite-volume discretization approach and Software FLUENT. The PISO approach was used for pressure-velocity coupling. The dynamic simulation of gear churning process was realized by using VOF two-phase flow and dynamic mesh techniques. The effects of gear rotational speed, immersion depth, lubricating oil viscosity and the rotational direction of gear on flow field within the gearbox were studied.The results show as follows:near the small-gear end of the casing wall surrounding, a flow rotating with a contrary path to the small-gear is generated, while the flow near the big-gear end of the casing wall surrounding is almost stationary. Lubricating oil is stirred up more quickly with increasing of the gear rotational speed; along with lengthening of the immersion depth, more lubricating oil is stirred up and moves with the big-gear wheel towards the meshing area. After some time, the distribution of oil stabilizes. For immersion depth less than three times of the tooth depth, large lubricating oil pellet gathers along the casing wall; for immersion depth reaching three times of the tooth depth, small oil drops could be found in the gearbox internal space, and some oil drops exists in the meshing area which is more conducive to the gear meshing area lubrication. For higher viscosity lubricating oil, more oil adheres to the big-gear teeth flank and circulates with the big-gear motion. For low viscosity lubricating oil, the lubricating oil is easier to get thrown to the casing wall, and eventually adheres to the casing wall uniformly. In the reverse condition, it is more conducive for lubricating oil spreading to the gearbox internal space. Air pressure around the ventilator fluctuates about the standard atmospheric pressure, and its change trend is almost without any rules to follow. Taking the labyrinth seal at the small-gear motor end the driving gearbox motor of the high-speed EMU as the research object, the numerical simulation model of the labyrinth seal with the oil thrower was set up, which was a fully compressible, two-dimensional axisymmetric swirl flow. The distribution of flow field within the labyrinth seal cavity and the leakage characteristics were simulated by using the standard k-ε turbulence model along with enhanced wall treatment. The Navier-Stokes equation, and energy and turbulence equations were discretized with the finite-volume discretization approach and Software FLUENT. The SIMPLE approach was used for pressure-velocity coupling. The effect of the cavity depth on leakage was studied and the optimum cavity depth was determined. The effects of seal clearance, pressure difference and rotational speed on leakage were also studied. The results show as follows:Along with lengthening of the cavity depth, the leakage firstly falls down and then rises up; as the seal clearance decreases, the seal performance becomes better; the leakage increases with increasing of the pressure difference; under the condition of without considering the temperature rise, the rotational speed shows no significant influence on leakage however, raising the rotational speed improves sealing performance.