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 byp...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.展开更多
基金financially supported by the National Science and Technology Major Project (No. J2019-Ⅱ-0004-0024)Youth Innovation Promotion Association CAS (No.202043)。
文摘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.
