| Modern aeroengine put forward technical requirements of high load and high stability for compressor,however,there are some contradictions between high load and high stability,high load often makes the compressor stability margin reduced,therefore,exploring advanced technology and clarifying the corresponding mechanism for expanding stability has important guiding significance to improve the load and stability of compressor.Taken NASA Rotor 67 as the research object,this paper carried out the investigation of improving performance for transonic axial flow compressor with slot casing treatment under unsteady numerical simulation method.The content of this article is divided into the following four points: 1.Revealing the mechanism of internal flow instability for transonic axial flow compressor with solid wall under different rotational speeds;2.Clarifying the mechanism of improving performance for transonic axial flow compressor with reversed blade angle slot under different rotational speeds;3.Through orthogonal test design and range analysis,exploring the influence ranking,optimal level and best combination of each design parameters for slot casing treatment under different rotational speeds;4.Through the control variable method,investigating the effects of single design parameter changing for slot casing treatment on the mechanism and ability of expanding stability under design rotational speed.Hoping to provides the theoretical basis of integrated design for new generation compressor and casing treatment.Through the above research,this paper draws the following conclusions:1.The instability mechanism of solid wall.The mechanism of internal flow instability for NASA Rotor 67 with solid wall under different rotational speeds are equal,are all induced by the blockage and fluctuation formed by leakage flow diffusing to the pressure surface of adjacent blade tip,belonging to a type of spike stall,but the forms are different:(1).The blockage resulted from the interference between leakage flow and shock wave is the main mechanism under 100% design rotational speed,and the shock wave occupies dominant factor at this time;(2).The blockage resulted from leakage vortex broken is the main mechanism under 80% design rotational speed,and leakage vortex occupies dominant factor at this time;(3).The blockage resulted from leading edge overflow is the main mechanism under 60% design rotational speed,and leakage vortex occupies dominant factor at this time.Besides,there doesn't exist unsteady fluctuation under 100% design rotational speed,while the unsteady fluctuation is shown the self-excitation unsteadiness of leakage vortex under 80% and 60% design rotational speeds.2.The mechanism of expanding stability with reversed blade angle slot.All reversed blade angle slots all expand the stability margin of NASA Rotor 67 and the mechanism are basically equal under different rotational speeds,but all of them reduce the peak efficiency of NASA Rotor 67.Though feeling and changing the pressure difference of blade tip passage axial direction,circumferential direction and between blade tip suction/pressure surface by the reversed blade angle slot,on the one hand,the driving force of leakage flow is changed and the negative effect of corresponding leakage vortex is weaken,on the other hand,the suction and injection effect of air flow on the blade tip passage are carried out,which blowing off and stimulating the low velocity air flow of blade tip passage,thus eliminating the blockage resulted from leakage flow diffusing to the pressure surface of adjacent blade tip when solid wall,in this way,improving the flow field of blade tip passage and expanding the stability margin of NASA Rotor 67.The reversed blade angle slot is shown to increase the blade tip load under 100% and 60% design rotational speeds,while the reversed blade angle slot is shown to reduce the blade tip load under 80% design rotational speed,a part of energy provided by the reversed blade angle slot is used to eliminate the leakage vortex broken,which resulting the effect of expanding stability for the reversed blade angle slot is lower under 80% design rotational speed than 100% and 60% design rotational speeds.The suction and injection effect of the reversed blade angle slot to the air flow of blade tip passage must be mixed with the mainflow of blade tip passage under different rotational speeds,which will bring tragic loss,in addition,the backflow inside the reversed blade angle slot will also bring loss,the combined effect between these will reduce the efficiency of NASA Rotor 67.Although the reversed blade angle slot eliminates the unsteady fluctuation of NASA Rotor 67 when solid wall under different rotational speeds,its suction and injection effect bring new unsteady fluctuation.3.The investigation of orthogonal test design for slot casing treatment.In addition to SCT1 doesn't have the ability of expanding stability under 80% design rotational speed,all slots have the ability of expamding stability under different rotational speeds,but all bring efficiency losses.(1).The result of orthogonal test design is that the effect of expanding stability for SCT4 is the best under 100% design rotational speed,about 30.15%,while the result of range analysis is that the effect of expanding stability for SCT10 is the best under 100% design rotational speed,about 28.80%,the absolute error is about 1.35%.The results of orthogonal test design and range analysis are all that the effect of expanding stability for SCT3 is the best under 80% and 60% design rotational speeds,about 27.89% and 29.35% respectively.(2).The main order of each factor is listed below under 100% design rotational speed: Cod>Angle>Depth>Area;The main order of each factor is listed below under 80% and 60% design rotational speeds: Area>Depth>Angle>Cod.4.The investigation of single design parameter for slot casing treatment.Slot casing treatment with different design parameters all expand the stability margin of NASA Rotor 67,but all reduce the peak efficiency of NASA Rotor 67.(1).As the axial deflection angle of slot changes from negative to positive,the ability to expand stability weakens gradually,and the loss of peak efficiency also reduces gradually,its suction effect is firstly enhanced and then weakened,while its injection effect enhanced gradually.(2).As the reversed blade angle slot extends forward or backward,the ability to expand stability weakens,and the loss of peak efficiency also reduces,its suction and injection effect are all weakened.(3).As the depth of the reversed blade angle slot increases,the ability to expand stability is firstly enhanced and then weakened,and the loss of peak efficiency is also firstly increased and then reduced,its suction and injection effect are all firstly enhanced and then weakened.(4).As the open area ratio of the reversed blade angel slot increases,the ability to expand stability enhances gradually,and the loss of peak efficiency also increases gradually,its suction and injection effect are all enhanced gradually. |
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