低温轴承润滑模型及快速起动理论与试验

Theoretical and Experimental Study on the Lubrication Model and Transient Start-up Process of the Cryogenic Rolling Bearing

液体火箭发动机高速涡轮泵的起动是在高压、低温等极端工况下的典型瞬态起动,极易导致其支承轴承的失效。本文构建了低温滚动轴承全液膜润滑和起动摩擦力矩的求解模型,获得了在特定工况下不同滚动体位置的液膜压力分布和最小液膜厚度等;计算得到了起动过程不同载荷和转速下特定低温轴承的起动摩擦力矩,并以此提出了确保轴承瞬态安全起动的最小径向预载方法。开展了液氮工况下的两组快速起动低温滚动轴承的试验测试,获得了高速起动下轴承的动态响应特征,其结果定性地验证了最小径向预载定义方法的合理性;动态响应的快速特征提取也表明了轴承在起动阶段的失效可能为局部碰磨,甚至存在不同轴承组件间严重的金属摩擦或者刮擦。研究结果对于提高低温液体火箭发动机高速涡轮泵的安全服役性能具有重要的理论和试验价值。

The start-up process of the high-speed turbopumps for the liquid rocket engine is a typical transient start-up process under the harsh conditions, such as high pressure and cryogenic, which easily leads to the failure of the support bearings. The lubrication model and the friction-torque model for expressing the start-up process of the cryogenic roll-bearing are constructed, and the fluid film pressure distribution and the minimum film thickness for the different rolling elements are obtained under the specific operating conditions. The start-up friction-torque of a specific cryogenic rolling bearing under the different loads and speeds is calculated,according to which a method for defining the minimum radial preload to ensure the bearing’s safety in the transient start-up processing is proposed. Two sets of experimental tests for the rolling bearing under the transient start-up and cryogenic nitrogen condition are carried out, and the the dynamic responses of the bearing are obtained. The experimental results qualitatively verify the reasonablenes of the above defined minimum radial preload for the cryogenic bearing. The fast feature extraction results of the dynamic responses also indicate that the failure of the bearing in the start-up processing may come from a localized rubbing, or even from serious metal friction or scraping between the different bearing components. The study has an important theoretical and experimental value for improving the safe service performance of the high-speed turbopumps in the cryogenic liquid rocket engine.