随着航空发动机推重比不断提高，高负荷单级压气机的流动与损失问题成为研究热点。叶栅负荷的提高意味着粘性效应、逆压梯度、非定常特性以及复杂的几何构型主导了流场以复杂的分离流动与旋涡结构为主要特征，而上述典型流动从根本上影响着压气机的工作性能。因此，在叶栅负荷提高的前提下如何通过合理选取设计参数及其匹配关系，有效组织端区二次流动实现高效稳定流动，是提升高负荷叶栅性能需要解决的关键问题。弯曲叶片通过改变端区压力场合理有效的组织三维流动改善和提升叶栅性能。弯叶片在常规叶栅设计参数选择范围内的基础研究和工程设计工作已经表明：弯叶片对压气机叶栅和多级压气机整体性能的提升有着显著效果。但是，在非常规叶栅参数范围内，弯曲叶片和叶栅设计参数的耦合作用对端区压力场、附面层发展机制、旋涡组成及其发展机制、角区分离控制方法、叶栅阻塞和失速工况下的流场特征的影响仍然有待探讨。 本文借助弯叶片对端区压力场的重构作用，采用经实验结果校核的数值模拟方法进行了大量的弯曲叶栅方案计算。分析了不同叶栅参数下弯曲叶栅流场结构的影响，探讨非常规设计参数范围下的高负荷流动中的附面层、旋涡运动的发展机制及其控制机理；建立弯叶片设计参数和传统关键叶栅设计参数与叶栅损失、端区流动间的依变关系。 首先分析了叶片弯曲对叶栅流场结构的演化及叶栅损失的影响。结果表明：角区分离为开式分离的低负荷叶栅中，端区损失的主要来源是通道涡卷吸端壁附面层内低能流体产生的高损失。正弯叶片增强了叶片径向压力梯度，削弱吸力面分离涡，但前缘马蹄涡增强，前缘进口段附面层增厚，端壁损失增加；同时栅内端壁上气流的横向运动增强，导致叶栅通道涡增强，通道涡起始位置前移，强度和尺度增加。通道涡卷积的低能流体产生的高损失及尾缘脱落涡内低能流体产生的叶型损失占据主导，因此叶片弯曲无法获得积极效果。随着负荷的增加，马蹄涡和通道涡增强，角区分离由开式分离向闭式分离转变，吸力面分离涡和集中脱落涡增强，分离起始点前移。叶栅高损失主要来源于吸力面分离涡和集中脱落涡。叶片正弯后，尽管端壁横向压力梯度继续增强，横向二次流增强，尺度和强度增强，尾缘回流强度和范围增加，但有效削弱了角区分离流动，减小吸力面分离涡和集中脱落涡，使叶栅损失有效降低，提升叶栅的扩压能力。冲角进一步增加，角区分离突变为角区失速甚至叶栅失速。正弯叶片推迟了角区失速的发生，吸力面上分离形式由角区闭式分离转变为吸力面尾缘分离，叶展中部低能流体严重堆积，造成叶栅总损失的增加。叶栅失速后，端壁回流前移至前缘，通道涡消失，但尾缘出口出现柱状的流向涡，卷积低能流体流出叶栅，叶栅损失继续增加，损失主要来源于吸力面分离涡和流向涡与叶展中部附面层的掺混。 其次，分析不同参数对叶栅流场结构与性能参数的影响。①稠度降低，叶栅负荷增强，横向压力梯度增强。大负冲角下，角区分离流动较弱，稠度降低，相邻叶片距离减小，角区分离流动强度减弱，通道涡起始位置略有后移，叶栅损失减小；随着冲角增加，叶栅负荷增强，角区分离流动增强，吸力面分离涡和集中脱落涡增强，叶栅损失增加。②展弦比降低显著增加了吸力面分离涡和集中脱落涡的尺度，但涡量强度略有降低；马蹄涡吸力面分支耗散位置向下游迁移，但压力面分支耗散消失位置前移；通道涡的的起始位置前移，但其强度略有减弱。叶栅损失的主要来源吸力面低能流体的堆积造成叶栅负荷降低，静压升降低。正弯叶片减小了吸力面分离涡和集中脱落涡强度和尺度，同时增强了通道涡。随着展弦比降低，通道涡起始位置后移，强度和尺度有所减小，通道涡造成的损失降低。③进口马赫数增加，附面层的发展速度降低，但叶栅角区分离流动增强，因此存在一个使叶栅损失最小的进口马赫数。正弯叶片减小角区分离流动，最佳弯角随进口马赫数的增加而增大。 ④几何折转角增加，叶栅负荷增加，叶栅角区分离流动增强，角区分离由开式分离向闭式分离转变。叶片弯曲增强了径向压力梯度，减小了角区分离流动，使分离流动由闭式分离向开式分离转变。特别是在大负荷叶栅条件下(低稠度、低展弦比、大折转角)正弯叶片能够有效降低叶栅端区二次流损失，恢复端区叶栅扩压能力，提升叶栅工作性能，但同时叶展中部叶型损失有所增加。 最后，分析叶栅几何及气动参数及叶片弯曲对叶栅最小损失冲角，最小损失冲角下扩压因子和总压损失系数以及临界冲角、临界冲角下性能参数和正冲角稳定工作范围间的影响。运用回归分析的方法建立相应的最小损失冲角关系式，扩压因子关系式和总压损失系数关系式，建立弯叶片设计参数和传统关键叶栅设计参数与性能参数的依变关系，较为准确预测弯曲叶栅的最小损失冲角及该工况下叶栅性能。叶片弯曲打破了直叶片栅内参数的平衡关系，丰富了叶栅的设计方案。最小损失冲角下，正弯叶片能够获得更高的扩压，更低的损失和更少的叶片数。将设计工况叶栅性能参数与叶栅正冲角稳定工作范围结合分析，揭示高负荷宽工作范围弯曲叶片设计方案的参数匹配关系。结果表明，低稠度、低展弦比的高负荷叶栅中采用正弯叶片能够在保证设计工况扩压能力的条件下既减小设计工况叶栅损失，减小叶片数，又能扩大叶栅稳定工作范围，为高负荷扩压叶栅设计提供一定技术支撑。 关键词：扩压叶栅；高负荷叶栅；叶栅参数；弯曲叶片；角区分离；角区失速；叶栅损失；扩压因子

 With the increase of thrust-weight ratio of aero-engine,the flow and loss of high-load single stage compressor becomes a research hotspot. The increase of cascade load means that the viscous effect, adverse pressure gradient, unsteady characteristics and complex geometric configuration dominate the flow field with complex separated flows and vortex structure as the main characteristics, which fundamentally affect the compressor performance.Therefore, under the premise of improving the cascade load, how to effectively organize the secondary flows in the endall corner to achieve efficient and stable flows by reasonably selecting design parameters and the matching relations is the key problem to be solved to improve the performance of the high-load cascade. Curved blade can reasonably and effectively organize the three-dimensional endwall comer flow to improve the performance of the cascade, by changing the pressure field distribution in the endwall corner region. The basic research and engineering design work of curved blade in the range of conventional cascade design parameters have shown that curved blade has a significant effect on the overall performance improvement of compressor cascade and multistage compressor. However, within the range of unconventional cascade parameters, the influence of the coupling effect of curved blade and cascade design parameters on the corner pressure field, boundary layer development mechanism, vortex composition and its development mechanism, separation flow control method, flow field characteristics under cascade choke and stall conditions remains to be discussed. In this paper, by means of the effect of curved blade on the pressure field reconstruction in the endwall corner region, a large number of curved cascade programes are calculated by numerical simulation method validated by experimental data. The variation of the flow field structure in curved blades at different cascade parameters is analyzed, the development mechanism of boundary layer and vortex motion and the high-load flow control mechanism under unconventional design parameters are discussed, and the relationship between curved blade design parameters, traditional critical cascade design parameters and cascade end wall corner flow and flow losses is established. Firstly, the influence of blade curving on cascade flow field structure evolution and cascade flow loss was analyzed. Results show that in the cases of loa-load cascade with open cornenr separation flow, the main source of endwall flow loss is caused by the low-energy fluid in the end-wall boundary layer suction by passage vortex. Positive curved blade enhances the radial pressure gradient of the blade and effectively weakens the boundary layer accumulation in the suction surface separation vortex(SSV) and concentrated shedding vortex(CSV), thus reducing the loss. However, the leading edge horseshoe vortex are increased, the inlet boundary layer at the leading edge is thickened and the endwall loss is increased. At the same time, the airflow transverse motion on the endwall of the cascade is enhanced, which leads to the enhancement of the passage vortex and the starting position of the passage vortex moves forward and conforms to the position of the lowest pressure point on one side of the suction surface. The high loss caused by the low-energy fluid convolution in the passage vortex and the profile loss caused by the accumulation of low-energy fluid in the middle of the blade span are dominant, so curved blade cannot achieve positive effects. With the increase of blade load, horseshoe vortexes and passage vortex increase, corner separation flow changes from open separation to closed separation, suction surface separation vortexes and concentrated shedding vortexes increase, and separation starting point moves forward.The high loss of cascade is mainly caused by the suction surface separation vortex and the concentrated shedding vortex. After the blade being curved positively, although transverse pressure gradient of endwall continues to be increased, transverse secondary flow is increased, whose scale and strength are increased,and trailing edge severse flow strength and range are increased, the separation flow in the corner region is effectively weakened, the separation vortex on the suction surface and the concentrated shedding vortex are reduced, the cascade loss is effectively reduced, and the diffusing capacity of the cascade is improved. With the increase of incidence angle, the corner separation flow breaks down into corner stall or even cascade stall. Positively curved blade delays the occurrence of corner stall. With incidence increasing, the separation form changes from closed separation on corner region to trailing edge separation on the suction surface,and the low-energy fluid in the middle of the blade blade seriously accumulates, resulting in an increase of total loss. After the stall happening, the endwall backflow moves forward to the leading edge and the passage vortex disappears. But columnar streamwise vortex appears at the outlet of the trailing edge, and the convolutional low-energy fluid flows out of the cascade, and the cascade loss continues to increase. The loss is mainly caused by the mixing of the suction surface separation vortex and the streamwise vortex with the boundary layer in the middle of the blade blade. Secondly, the influence of different parameters on the flow structure and performance parameters of cascade are analyzed, including the impact of the minimum loss incidence and the accordingly performance parameters, as well as the critical incidence and performance parameters. (1) Solidity decreases, cascade load increases, transverse pressure gradient increases. Under a large negative incidence angle, the separation flow in the corner area is weak, when decreases, the distance between adjacent blades decreases, the corner separation flow intensity weakens, the passage vortex onset moves dowstream slightly, and the cascade loss decreases. As the incidence increases, the cascade load increases further, the corner separation flow increases. When the solidity decreases, the separation flow increases and the suction surface separation vortex concentrated shedding vortex increases, the cascade loss increases. (2) The decrease of aspect ratio significantly increases the scale of suction surface separation vortexes and concentrated shedding vortexes, but the vorticity strength is slightly reduced. The main source of cascade flow loss is the accumulation of low-energy fluid on suction surface, which leads to the decrease of cascade load and static pressure rise. In straight blade,the passage vortex onset moves forward while the intensity and scale decrease slightly. The dissipation position of the suction surface branch of horseshoe vortex moves downstream, while the dissipation position of the pressure surface branch moves forward. Positively curved blade reduces the intensity and scale of suction surface separation vortex and concentrated shedding vortex, while enhances the passage vortex. With the aspect ratio decreases, the passage vortex onset moves backward, the strength and scale decrease, and the loss caused by the passage vortex decreases. (3) With the increase of inlet Mach number, the development speed of boundary layer decreases,but the separation flow in cascade comer region is enhanced, so there is an inlet Mach number that can minimize the loss of cascade. The optimal angle increases with the increase of inlet Mach number. (4) With camber anlge increasing, the cascade load increases, the corner separati on flow strengthens, the corner separation transforms from the open separation to the closed separation. Positively curved blade enhances the radial pressure gradient and reduces the separation flow in the corner region, so that the separation flow changes from closed separation to open separation. In particular, under the condition of large-load cascade (low solidity, low aspect ratio, and large camber angle), positively curved blade can effectively reduce secondary flow loss in the end area of cascade, restore the diffuser capacity of end-area cascade, and improve the performance of cascade, but at the same time, blade profile loss in the middle part of blade development is increased. Finally, the influence of the geometric and aerodynamic parameters of the cascade and the positively curved blade on the minimum loss incidence angle of the cascade,the diffusion factor and the total pressure loss coefficient under the minimum loss incidence angle, the performance parameters under the critical incidence angle and the stable working range of the positive incidence angle were analyzed. Using regression analysis method to establish the correlation of minimum loss incidence, corresponding diffusion factor and total pressure loss coefficient, and establish the variable relationship between performance parameters and curved blade design parameters as well as the traditional key cascade design parameters, which can more accurate predict the minimum loss condition. Curved blade breaks the balance of parameters in straight blade cascade and enriches the design scheme of blade cascade. Under the condition of minimum loss incidence, curved blade can obtain higher diffuser pressure, lower loss and fewer blade number. Based on the analysis of cascade performance parameters of at design conditions and the positive stable working range, the parameter matching relation of curved blade design scheme with high load and wide working range is revealed. Results show that the use of positively curved blade in the high-load cascade with low solidity and low aspect ratio can not only reduce the cascade loss and blade number in the design condition,but also expand the stable working range of the cascade, providing some technical support for the design of high-load diffuser cascade. Keywords: Compressor cascade; High-load cascade; Cascade parameters; Curved blade; Corner separation; Corner stall; Total pressure loss; Diffusion factor