Investigation Of Fence To Control Flow Structure In Compressor Cascade And Stage

The complex secondary flow structure in compressor cascades can restrict the further im-provement of the efficiency and circumscribe the development of the lightweight and energy-saving design for gas turbines.The flow control technology is one of the main measurements to improve the performance of compressors.Without combining other flow control technology or applying repeated arrangement,most of the passive flow control technology is difficult to achieve significant performance improvements under varying operation conditions in high-loaded tran-sonic compressors.In this paper,the typical highly-loaded lineal cascade and axial compressor stage were selected as the research object.To control the complex secondary flow phenomena near the endwall and blade suction surface,multi-object optimization for its overall dimensions was applied to the new-type fence based on the design philosophy of traditional fences.The nu-merical study combined with topological analysis was used to explore the control effect of the new-type fence on cascade secondary flow.The research purpose is to establish an optimization design scheme to achieve the new-type fence with multi-condition flow control effect,which pro-vides a new method and new idea for the passive flow control of high-performance compressors and has important theoretical value and practical significance for the design of highly-loaded and transonic compressors.The optimization design of the triangular prism endwall/suction surface fence（TEF/TSF）in a highly-loaded linear cascade was firstly studied.The optimal case of TEF can reduce the total pressure loss coefficient under the operation range of-9。～-3。incidence,while the optimal TSF works for all operation conditions（-9。～+3。）.The results show that both the optimal TEF and TSF can reduce the total pressure loss coefficient of prototype cascade by 12.30%and 10.41%,respectively,under the design condition.For the negative incidence,the loss is reduced by 3.44%and 5.91%.However,TEF leads to an increase in the loss by 3.41%while TSF decreases it by0.42%at positive incidence.This result demonstrates the design of the new-type fence is effective as a passive control technique for the highly-loaded compressor cascades,and the feasibility of the proposed optimal design process with the rationality of the aerodynamic analysis framework is validated.It is found that the new-type design can alleviate the local loss compared to a greater extent than the traditional rectangular design.Secondly,the transonic compressor stage was used as the research object to explore the appli-cation effect of TEF.Based on the same optimization design process,both the optimal TEF_shroudand TEF_hubcan improve the compressor efficiency at near choked condition,design condition,and near stall conditions within a small range of 0.08%～0.55%.Meanwhile,the stability mar-gin of the stage with TEF_shroudis improved by 3.13%,but TEF_hubnarrows 2.12%of the margin.Although the endwall crossflow in the compressor stage is opposite to it in linear cascade,there are similar control mechanisms in the transonic stage and high-speed cascade:1)Blocking effect:The windward side of TEF facing to endwall crossflow blocks the movement of the boundary layer with low-energy,which develops into the fence vortex with the same property of stream-wise vorticity as the endwall crossflow.2)Inducing effect:In the transonic compressor stage,the leeward side of TEF will induce another fence vortex,rotating in the same direction as the one caused by the block effect,which can be observed in the highly-loaded cascade.However,there is another counter-rotating vortex induced by the TEF due to the stronger crossflow in the linear cascade.This vortex can interact with crossflow and low energy from corner separation.3)Steering effect:When the form of the corner is open,the low-energy local separation induced by the TEF will merge into the corner region and steer the development of the corner region to the endwall,thereby the tendency to expand to the suction surface will be reduced.Finally,taking the transonic compressor stage as the research object,TSF_upperand TSF_lowerwere optimized through the multi-object optimization progress.The results show that the effi-ciency of a stage can be improved by～1%under the control of the optimal TSF_upperat three typical conditions.Meanwhile,the optimal TSF_lowerhas a smaller improvement as～0.4%.Based on the topological analysis,the flow control mechanism of TSF in linear and stage cascade is shown as follows:1)Blocking effect:The radial flow on the suction surface in the highly-loaded linear cascade and in the upper channel of the transonic stator has the same direction pointing from the endwall to the blade midspan,hence the side of the TSF closed to the endwall can block the radial flow,which forms into the fence vortex with the same rotating direction as the radial flow.2)Inducing effect:In both two cascades,the other side of the TSF closed to blade midspan will induce the flow crossing over the top of TSF into a counter-rotating vortex compared to the radial flow.3)Steering effect:When the separation form of corner separation is open or transitional,TSF can steer the low-energy fluid of corner separation to the suction surface and away from the endwall.Additionally,in the circumstance of the corner separation with a small scope,such as the design point or the near stall point,the corner separation will be divided into three or two parts by the steering effect of TSF.