Investigation On Flow Separation Loss And Control Methods In Axial Compressor Stators

With the increasing demand of high-pressure-ratio aero-engine compressors,the three-dimensional and unsteady characteristics of compressor flow become more and more prominent.The increase of single-stage blade loading would aggravate the leakage flow in the rotor blade tip region and the separation flow in the stator passage,degrading the aerodynamic performance of compressors.In this paper,the separation flow and control methods in axial compressor stators are numerically studied.The contents of this study are summarized as follows:In the first part of this paper,the researches on flow separation,flow loss models,and flow control methods are introduced and summarized.It is found that there is lack of a valid method,which can guide the design of flow control method based on the quantitative analysis of flow separation loss.In the second part of this paper,the effect of blade loading on corner separation and the corresponding flow loss are investigated.The Zierke&Deutsch cascade and the stator of a 1.5-stage compressor are selected as numerical models.The results show that the flow separation and loss distribution in the stator passage are closely related to the blade loading.For the Zierke&Deutsch cascade with a large blade turning angle,when the incidence angle increases,the flow separation occurs near the suction surface of the blade.For 1.5-stage compressor stator,when the incidence angle increases,the corner separation occurs in the region between blade suction surface and end wall,and the induced flow loss increases.In the third part of this paper,a new approach of prescreening control methods for flow separation in axial compressor stators is established based on the entropy generation rate loss model.With this new approach,one can firstly quantitatively analyze the flow loss in the compressor stator,and then guide the initial design of control methods according to the flow loss distribution in the compressor.The new approach was verified by two simulation cases.The flow loss generated in the 1.5-stage compressor stator and in the Zierke&Deutsch cascade is quantitatively analyzed,and a reasonable control method is accordingly suggested for the 1.5-stage compressor stator and the Zierke&Deutsch cascade,respectively.A total of three different control methods are simulated and compared.The results show that the control method suggested according to the quantitative calculation of flow loss is the best choice for alleviating the flow separation in the blade passage.In the fourth part of this paper,the design parameters of end-wall jet are optimized to further reduce the flow loss generated in the 1.5-stage compressor stator.The NSGA-Ⅱ algorithm was used in the optimization process.A total of six parameters,including the length,axial position and airflow angles of the two end-wall jet slots are optimized to achieve the highest efficiency at design and near-stall operating points.The optimal end-wall jet increases the polytrophic efficiency of the compressor at the peak efficiency and near-stall conditions by 12.40%and 19.55%,respectively.To sum up,a new approach to guide the design of flow separation control methods is established in this paper,which contains three steps:flow loss analysis-control method prescreening-control method optimization.The flow loss is firstly calculated,and the end-wall jet and blade Coanda jet are then suggested for a 1.5-stage compressor stator and Zierke&Deutsch cascade,respectively.Finally,based on NSGA-11 algorithm,the design parameters of the endwall jet are optimized to further reduce the flow loss generated in the 1.5-stage compressor stator.