Background

A turbopump is an important and critical component in the liquid rocket engine assembly where a small deviation in the system parameters such as unbalance level, dimensional tolerances, rotor–stator clearance, etc. can have significant influence on its dynamic behavior and may lead to various faults such as rub. Hence, a detailed rotordynamic study is essential for the entire operating speed range.

Purpose

Most of the earlier studies on rotor-stator rub were carried out for simplified rotor models and its implementation on a rotor assembly such as turbopump will be of immense practical relevance for researchers and engineers. Contact mechanics-based Lagrange multiplier method is used to enforce the contact constraints that incorporate compliant stator model which respond to the axial and lateral forces during contact.

Methods

A full-scale cryogenic engine turbopump rotor system consisting of turbines, impellers, inducer, bearings and seals is modelled using FE framework to investigate the rotor–stator contact interaction during coast-up. The stator model the a circumferentially positioned beams around rotor disc and investigated using more realistic contact mechanics-based Lagrange multiplier method.

Results

The eigenvalue analysis on the FE model gives the rotor critical speeds and the corresponding vibration modes. The constraints imposed by the stator beams and tangential friction due to rub cause a continuous phase shift in the rotor vibration during contact. The physical insights into the distinct rotor vibration features in the two lateral directions are discussed in detail. The influence of clearance level on the observed backward whirl nature of the turbine is established through a full-spectrum analysis.

Conclusion

The tighter clearance between rotor and stator gives rise to dominating presence of backward whirl components that may be detrimental to the fatigue life of the shaft due to stress reversal. Duration of the contact interaction is found to decrease significantly with increase in rotor–stator clearance and decrease in friction coefficient. With tighter clearances, the influence of stator stiffness becomes more significant and the rotor response during contact exhibits nonlinear and complex vibration.

中文翻译：

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低温发动机涡轮泵惯性滑行运行过程中的摩擦现象研究

背景

涡轮泵是液体火箭发动机总成中的重要组成部分，系统参数（例如不平衡水平，尺寸公差，转子-定子间隙等）的微小偏差可能会对其动态行为产生重大影响，并可能导致擦等故障。因此，详细的转子动力学研究对于整个运行速度范围至关重要。

目的

转子-定子摩擦的大部分早期研究都是针对简化的转子模型进行的，并且在诸如涡轮泵之类的转子组件上的实施对研究人员和工程师具有巨大的实际意义。基于接触力学的拉格朗日乘数法用于加强接触约束，该约束包含了顺应性定子模型，该模型响应接触过程中的轴向力和横向力。

方法

使用有限元框架对由涡轮，叶轮，诱导器，轴承和密封件组成的全尺寸低温发动机涡轮泵转子系统进行建模，以研究滑行期间转子与定子的接触相互作用。定子对围绕转子盘的沿圆周方向定位的梁进行建模，并使用基于接触力学的逼真的拉格朗日乘数法进行了研究。

结果

FE模型的特征值分析给出了转子的临界转速和相应的振动模式。定子梁施加的约束以及由于摩擦引起的切向摩擦会导致接触期间转子振动的连续相移。详细讨论了在两个横向方向上不同的转子振动特征的物理见解。通过全频谱分析确定了间隙水平对观察到的涡轮后向涡流特性的影响。

结论

转子和定子之间更紧密的间隙导致主要存在向后涡流部件，这可能会由于应力逆转而损害轴的疲劳寿命。发现接触相互作用的持续时间随着转子-定子间隙的增加和摩擦系数的降低而显着减少。间隙越小，定子刚度的影响就越明显，并且接触期间的转子响应会表现出非线性和复杂的振动。