Influence of Internal Bypass Conditions on the Matching Characteristics of Front and Rear Fans in the Three-Bypass Variable Cycle Engine 

  • WANG Haoran ,
  • ZHAO Shengfeng ,
  • LUO Qiaodan ,
  • ZHOU Shiji ,
  • LU Xin’gen
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  • 1. Key Laboratory of Light-Duty Gas-Turbine, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China
    2. University of Chinese Academy of Sciences, Beijing 100190, China
    3. National Key Laboratory of Science and Technology on Advanced Light-duty Gas-turbine, Beijing 100190, China

Online published: 2025-05-06

Supported by

This study was financially supported by the National Science and Technology Major Project (No. J2019-II-0004-0024) and Youth Innovation Promotion Association CAS (No. 202043).

Copyright

Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2025

Abstract

In this study, a three-dimensional numerical investigation was conducted on the front and rear fans of a three-bypass variable cycle engine under various speeds and internal bypass conditions. The impact of internal bypass conditions and speeds on the matching characteristics of the front and rear fans, as well as the factors limiting the variation of bypass ratio, are summarized. The findings reveal that for near stall, design point, and near choke internal bypass conditions, the operating point of the front fan tends to move towards near-stall while that of the rear fan moves towards near-choke when increasing external bypass back pressure. At design speed, external bypass blockage is identified as a limiting factor for increasing the bypass ratio at the internal bypass design point. Additionally, blockage caused by a significant amount of low-energy fluid at the suction surface of the rear fan stator leads to rear fan stall which limits further increase in bypass ratio at external bypass near stall condition. Similarly, leakage flow overflow passage at the top section of first stage rotor blade in front fan results in front fan stall, which restricts decrease in bypass ratio at internal bypass near stall condition. As corrected speed decreases, there is an upper-left shift observed in the curve depicting variation in relative back pressure with respect to change in bypass ratio due to the phenomenon “pre-surge and post-choke”. This indicates increased air flow into external bypass resulting in higher values for lower speeds. Furthermore, limitation on further increase in bypass ratio at external bypass near stall condition with decreasing speed can be attributed to transition from rear fan stall to external bypass blockage.

Cite this article

WANG Haoran , ZHAO Shengfeng , LUO Qiaodan , ZHOU Shiji , LU Xin’gen . Influence of Internal Bypass Conditions on the Matching Characteristics of Front and Rear Fans in the Three-Bypass Variable Cycle Engine [J]. Journal of Thermal Science, 2025 , 34(3) : 801 -818 . DOI: 10.1007/s11630-025-2111-8

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