# The Investigation of a New End Wall Contouring Method for Axial Compressors
## 5 Conclusions  
This study proposes a new end wall contouring method based on the secondary flow control mechanism established in previous research, then verified its effectiveness numerically in a cascade and experimentally in an axial compressor stage. The following conclusions were obtained:  
1. The idea of the new end wall contouring method is to define multiple standard surface \"units\" with particular effects on the end wall secondary flow. Then, we apply a weighted superposition to the units to obtain a comprehensive flow control effect. Compared with the traditional empirical method in the previous research, the design space of the new method enables the parametric end wall to control secondary flow intuitively in more than one local region with a proper amount of design variables, thus showing more advantages.
2. The numerical and experimental research indicates two primary mechanisms of applying the end wall contouring to control the corner separation, i.e., the local acceleration of secondary flow at the SS corner and the full-range deceleration of the secondary flow in the rear passage. The former will accelerate the corresponding secondary climbing flow on the SS, thus mixing with the low-energy separation flow and reducing the separation loss. The latter will suppress the accumulation of low-energy fluid of the boundary layer at the SS corner, thus relieving the local reverse flow. However, the above flow control may also be accompanied by the negative effect of the inverse pressure gradient at the front SS corner, which may seriously deteriorate the corner separation when it is under high incidence.
3. When applied to the stator casing end wall of an axial compressor, although the efficiency only increases on the right part of the operating map, the experiment results show that the intended control of secondary flow agrees with its actual effect and suppresses the corner separation under multiple operating conditions. Its effectiveness is thus verified. The reduction of efficiency at the small mass-flow-rate working points reflects a limitation of the new method and is probably associated with the characteristics of the current compressor stator.  
The number of design variables in the newly developed end wall contouring method is relatively small, and all of them show a clear and intuitive effect on the secondary flow. The next step of the research should consider the optimization process. Three-dimensional blading should also be included to overcome any shortages when suppressing the corner separation.  
Funding acquisition, H.Z. and W.C.; Software, Q.L.; Supervision, X.L.; Writing--original draft, F.Y. All authors have read and agreed to the published version of the manuscript.  
The work is funded by the National Natural Science Foundation of China (Grant No. 51906027, 52176036 and 52076179), Doctoral Initiation Research Funds of Liaoning province (Grant No. 2019-BS-027) and the Fundamental Research Funds for the Central Universities (Grant No. 3132022124).  
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.