Analysis Of Heat Generation And Cooling Of High-speed Ball Bearings For LOX/LH2 Rocket Engine Turbopump

Rolling bearing is an important rotating supporting part in general machinery.In the aerospace field,due to the continuous improvement in the performance of LOX/LH2 rocket engines,the requirements for turbopump have also been continuously increased,and high-speed ball bearings,which are key components of turbopump,have also become important parts influencing the reliability and performance of turbopump.High-speed bearings for turbopump are usually cooled with liquid hydrogen and liquid oxygen.They work under the harsh conditions of low temperature and difficult lubrication.In order to ensure their normal operation,the calorific value and cooling capacity of bearings need to be calculated.However,there is little information about the thermal analysis of the cryogenic bearing for turbopump.In this paper,a high-speed ball bearing for a turbopump of a LOX/LH2 rocket engine has been studied,and the mechanical properties,friction heat generation,and working temperature has been calculated.The cooling effect of cryogenic liquid hydrogen and normal temperature gas for ball bearing is analyzed,and the basis for the design of the turbopump and related experiments has been provided.In this paper,the pseudo-static modeling of high-speed ball bearings is firstly calculated,the force and the movement state are analyzed,the frictional power consumption inside the ball bearing is calculated,and the calculated results are used as the input conditions to perform the two-dimensional temperature field of the bearing.Based on these calculations,the three-dimensional flow field of the bearing under different coolant conditions has been calculated,and the influence of the ball bearing using conditions,heat generation and cooling of the bearing has been discussed.The following conclusions can be drawn:1)For the bearings calculated in this paper,the results of the total heat generation calculated by the lumped method and the local method are not much different.In the heat source of the bearing,the most important frictional power consumption comes from the self-rotation of the rolling elements,which leads to the obvious heating in the rolling element and the inner raceway contact area,forming a high temperature area.An increase in the axial load and the rotational speed of the bearing causes a significant increase in the frictional heat generation,while the radial load has no obvious effect on the frictional heat generation of bearing.2)During the heat exchange process of the bearing,the convection heat transfer of the coolant is the main heat transfer mode.So when the frictional heat of the bearing increases significantly,the temperature of the entire bearing does not rise significantly,but a clear high temperature area can be formed at the contact area between the rolling element and the inner raceway.In addition,an increase in the kinematic viscosity of the coolant also increases the power consumption and temperature of the bearing.3)There is a clear difference between the state of fluid flow when cryogenic liquid hydrogen and normal-temperature gas are cooled.Under the conditions of cryogenic liquid hydrogen cooling,the bearing works better.When the cooling flow of the single rolling element is increased or the pressure is increased,the cooling performance of the bearing can be improved.However,when the cooling flow rate of a rolling element reaches more than 14 g/s,it is of little use to continue to increase the cooling flow rate to improve the cooling effect.4)In the current calculation of normal temperature hydrogen,helium and nitrogen coolant,the bearing cooling effect is not as good as liquid hydrogen cooling,and in these three gases,hydrogen's cooling effect is the best;and the gas cooling bearing must be under high pressure conditions to achieve the need for cooling the bearing.For gas-cooled bearings,increasing the cooling flow does not necessarily improve the cooling of the bearing.Excess coolant can improve the heat dissipation in the non-contact zone,but it can also make the fluid temperature higher in the contact zone which is the high temperature area,which requires full consideration for the bearing effect.