Mechanism Investigation Of Holed Pulsed Suction To Control Flow Separations In A Highly Loaded Compressor Cascade

The compressor as one of the key components of an aero-engine has a high-tech,and has an important effect on the performance of the aero-engine.In modern compressor designs,the continually increasing blade load results in threedimensional unsteady flow separation and a decrease in aerodynamic efficiency,and even stall,surge and other dangerous aerodynamic instability.Therefore,on the basis of a deep understanding of the complex internal flow of compresso r,it is of great significance to develop advanced and feasible flow control technology to break the existing limit of compressor aerodynamic load,and in turn better integrate this flow control technology into the design system of compressor.Therefore,the holed pulsed suction(PS)is proposed,and this method is achieved by one suction hole arranged only on the end wall,which has the advantages of small suction rate and no damage to blade strength,this article mainly carried out detailed research work from the following aspects:Firstly,an experimental study on the effectiveness of PS for flow control is conducted herein using a low-speed wind tunnel.The results show PS provided better performance than SCS at the same suction flow rate.PS has two advantages over SCS:first,at the same suction flow rate,PS has a larger suction momentum than SCS during the suction phase,resulting in a stronger suction force and having a more profound effect on the flow characteristics;and second,owing to the introd uction of pulsed excitation to the suction,PS creates additional vortex structures that energize the boundary layer by transporting high momentum free-stream fluid near the wall,which results in controlling effectively three-dimensional flow separations.Moreover,while the PS and PB show different aerodynamic characteristics at different excitation parameters,their positive effects based on their optimal excitation parameters do not show marked differences.Besides,the passage vortex and concentrated shedding vortex has a significant effect on the scale of the high loss region,and are the main factors that contributed to the total pressure loss.The PV was suppressed,which is the primary reason for the improvement in aerodynamic performance and the reduction in total pressure loss.Secondly,in order to obtain more flow details and typical flow characteristics in the compressor passage,so as to further enhance the understanding of the mechanism of PS,based on the experimental study,Some important exicition parameters for the PS are investigated in detailed by numerical simulation.The PS and steady continuous suction(SCS)are studied to analysis comparatively the control effects of flow separations and their corresponding adaptability and flexibilit y under different incidence angles.The results show PS has the dependence of excitation parameters:the optimum frequency is an integer multiple of the natural frequency of vortex shedding;the control effect becomes more evident with the increasing of suction flow rate;the optimum excitation location is near the separation point of upper endwall,and if the excitation location is far from its optimum range,the control effect of flow separation will be weakened or even worsened.The control effect becomes more evident with the decreasing of pitch angle and the more benefical effect is achieved at ?=315°.Compared with SCS,PS provides a better control effect and shows better adaptability under different incidence angles at the same suction flow rate.One of the main reasons why PS has better control effect than SCS is is that the PS can "adapt" or "match" the unsteady characteristics of the flow field.Therefore,the PS shows a greater advantage in reconstructing and improving the flow state of the flow fi eld.Under the effect of PS,the flow field presents a forced oscillation phenomenon due to the "frequency locking" effect,which leads to a more orderly state of the flow field,and also the more significant the dominant frequency pulsation in the flow fi eld is suppressed,the greater the loss reduction is,and the more evident the control effect is.Moreover,the control effects of PS based on the different excitation models are slightly different,this main reason is due to the fact that the change rate and the maximum value of transient suction velocity have a certain correlation with the turbulent shear and viscous dissipation resulting in the loss.Besides,the PS,pulsed jet/blowing(PB)and synthetic jet(SJ)show different aerodynamic characteristics at different excitation parameters at the same control conditions.Compared with PB and SJ,PS has better adaptability and feasibility at different excitation parameters.Finally,the PS combined with negative bowed blades was proposed as a novel application of the compound flow control(CFC)approach with the aim of further enhancing aerodynamic performance of the compressor cascade and trying to integrate PS into the design system of compressor.The aerodynamic performance and energy consumption are evaluated by numerical simulation.The important parameters such as bending angle,excitation location,excitation frequency and suction flow rate are studied in detail.The results show that the CFC was more effective in improving the aerodynamic performance than the PS with the same control condition.With the ensuing optimization of the CFC,the total pressure loss coefficients were reduced by18% and a highest energy efficiency reached as high as 504%.