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工程设计学报
Chinese Journal of Engineering Design  2026, Vol. 33 Issue (1): 138-146    DOI: 10.3785/j.issn.1006-754X.2026.05.182
Mechanical parts and equipment design     
Mechanism analysis and relief measure verification of trapped-oil phenomenon in Roots pumps
Yulong LI1(),Anran SONG1,Luhao SONG2,Tianya LIU2
1.School of Mechanical and Electrical Engineering, Suqian University, Suqian 223800, China
2.School of Intelligent Manufacturing and Emergency Equipment, Jiangsu College of Safety Technology, Xuzhou 221011, China
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Abstract  

To address the problems of pressure pulsation, power fluctuation and flow instability caused by the trapped-oil phenomenon when Roots pumps transport high-viscosity hydraulic oil, it is necessary to clarify the trapped-oil mechanism and compare the differences in trapped-oil characteristics induced by different rotor profiles, and propose targeted mitigation measures, thus providing theoretical support for the structural optimization and working condition adaptation of Roots pumps. Firstly, according to whether there was a circular arc transition at the top and root of the rotor profile, it was divided into full working type (such as circular arc profile) and non-full working type (such as involute profile). At the same time, the rotor profile was constructed through parametric modeling, the key structural parameters were defined, and a unified mathematical equation was established. Then, the three-dimensional geometric model of the Roots pump was generated using Siemens NX software, and the CFD (computational fluid dynamics) simulation model was built by Pumplinx software to analyze the operating characteristics of the pump with hydraulic oil as the medium. Finally, square relief grooves were machined at the rotor root, and the differences in trapped-oil characteristics between the pumps with and without relief grooves were compared. The simulation results showed that significant trapped-oil phenomenon occurred in both types of Roots pumps: the maximum pressure increase of the pumps with involute and circular arc profiles was 113.3% and 68.7%, respectively, and no cavitation occurred. After opening the relief grooves, the instantaneous pressure fluctuation amplitude of the pump with involute profile was reduced by 29.5%, and the maximum pressure increase was decreased to 50.4%, whereas the average output flow rate was reduced by 1.2%. In summary, the trapped-oil hazard of non-full working rotor profiles was more serious, and the relief grooves at the rotor root could effectively suppress the trapped-oil phenomenon, but it would lead to a slight reduction in the output flow rate. The research results provide a theoretical basis and technical references for the engineering application of Roots pumps in the high-viscosity liquid transportation field.

Key words： Roots pump      trapped-oil phenomenon      pressure pulsation      rotor profile      relief groove     
Received: 01 August 2025      Published: 01 March 2026
CLC:  TB 752+.26  
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Yulong LI
Anran SONG
Luhao SONG
Tianya LIU
Cite this article:

Yulong LI,Anran SONG,Luhao SONG,Tianya LIU. Mechanism analysis and relief measure verification of trapped-oil phenomenon in Roots pumps. Chinese Journal of Engineering Design, 2026, 33(1): 138-146.

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https://www.zjujournals.com/gcsjxb/10.3785/j.issn.1006-754X.2026.05.182     OR     https://www.zjujournals.com/gcsjxb/Y2026/V33/I1/138


罗茨泵困油现象机理剖析与缓解措施验证

为解决罗茨泵在输送高黏度液压油时由困油现象引发的压力脉动、功率波动及流量不稳定问题，需明确其困油机理，对比不同转子轮廓下的困油特性差异并提出针对性缓解措施，从而为罗茨泵的结构优化与工况适配提供理论支撑。首先，按转子轮廓顶部与根部是否有圆弧过渡，将其划分为全工作型（如圆弧轮廓）与非全工作型（如渐开线轮廓）两类；同时，通过参数化建模方法构造转子轮廓，定义关键结构参数并建立统一数学方程。然后，利用Siemens NX软件生成罗茨泵的三维几何模型，并借助Pumplinx软件建立CFD（computational fluid dynamics，计算流体力学）仿真模型，以分析液压油介质下该泵的运行特性。最后，在转子根部开设方形卸荷槽，并对比有无卸荷槽时的困油特性差异。仿真结果表明，2种罗茨泵均存在显著的困油现象：渐开线和圆弧轮廓下泵的最大压力增幅分别为113.3%、68.7%，且均未发生空化现象；在开设卸荷槽后，渐开线轮廓下泵的瞬时压力波动幅度缩小了29.5%，最大压力增幅降至50.4%，但平均输出流量下降了1.2%。综上，非全工作型转子轮廓的困油危害更为严重，转子根部的卸荷槽可有效抑制困油现象，但会导致输出流量小幅衰减。研究结果可为罗茨泵在高黏度液体输送领域的工程应用提供理论依据与技术参考。


关键词： 罗茨泵,  困油现象,  压力脉动,  转子轮廓,  卸荷槽 
Fig.1 Parametric construction of rotor profile for Roots pump
参数数值参数数值
转子叶数3径向间隙/mm0.10
形状系数1.45啮合间隙/mm0.20
节圆半径/mm30轴向间隙/mm0.15
转子宽度/mm120轴孔半径/mm12
壳壁半径/mm43.5
Table 1 Key parameters of rotor profile and geometric model of Roots pump
Fig.2 Geometric models of Roots pumps
Fig.3 Roots pump simulation model and monitoring point setting
参数数值
液压油动力黏度/(Pa·s)0.03
液压油密度/(kg·m-3)850
液压油体积弹性模量/Pa1.5×109
液压油饱和蒸气压/Pa400
转速/(r/min)1 000
角速度/(rad·s-1)104.72
进口压力/Pa1.013 2×105
出口压力/Pa1.013 2×106
Table 2 Parameters of simulation medium and boundary condition
Fig.4 Performance simulation results of Roots pump
参数渐开线罗茨泵圆弧罗茨泵
p/Pa2 062~2.16×1061 794~1.71×106
?pmax/%113.368.7
?pmin/%98.098.2
P/W3 617~8 5293 340~8 396
Q???/(m3/s)0.010 280.010 16
Table 3 Comparison of medium pressure, input power and output flow rate of Roots pump
Fig.5 Relief groove structure in gear pump
Fig.6 Relief groove structure for involute Roots pump
Fig.7 Medium pressure curves of involute Roots pumps with/without relief grooves
参数无卸荷槽有卸荷槽变化率/%
p/Pa2 062~2.16×10620 461~1.52×106-29.5①
?pmax/%113.350.4-55.5
?pmin/%98.079.8-18.6
Q???/(m3/s)0.010 280.010 16-1.2
Table 4 Performance comparison of involute Roots pumps with/without relief grooves
 
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[1] Yulong LI,Luhao SONG,Tianya LIU,Anran SONG. Research on prediction models for limiting vacuum degree and its pre-pumping time of Roots pump[J]. Chinese Journal of Engineering Design, 2025, 32(6): 856-864.
[2] LI Yu-long, SUN Fu-chun. Research on H-shaped backlash structure on gear pairs for relief of trapped-oil in pumps[J]. Chinese Journal of Engineering Design, 2019, 26(1): 15-19,28.