# The Investigation of a New End Wall Contouring Method for Axial Compressors
## 4 Experiment on the Axial Compressor Test Rig
### Summary of the Effects of the End Wall Contouring  
According to the overall performance, the end wall contouring only benefits the right-side operating map of the compressor stage. At the BM point of the compressor, the end wall contouring increases the peak value of \(\sigma\) in the stator, thus making a 10.44% relative reduction of stator loss, which finally increases the overall efficiency by 0.45%. At the LM point, the decrease of \(\sigma\) shows the stator loss increases relatively by 1.95%. Thus, the overall efficiency of the stage decreases by 1.5%.  
However, although the efficiency does not increase in all the working conditions, the flow field shows that applying the new end wall contouring method can always improve the corner separation. The tested end wall static pressure shows that the end wall contouring suppresses the end wall secondary flow in the full range but accelerates the cross and climbing flow in the SS corner. The corner separation is thus reduced, and the total pressure loss coefficient in the end wall region reduces locally by 0.01-0.03 for both the operating points.  
For the reduction of efficiency at the LM point, the experimental data show it is likely a side effect of suppressing the corner separation. Because the relief of corner separation reduces the local blockage, the throughflow increases in the end wall region and decreases in the main flow. As a result, the main flow region is more \"throttled\", thus negatively affecting the control of loss. It should be noted that this side effect does not have to increase loss. Just as reported in [PERSON]'s research [7], if the main flow is robust, suppressing the corner separation will not increase the loss in the main flow region. Otherwise, it could induce a detrimental effect, as in [PERSON]'s research [18], where severe corner separation occurs in the opposite end wall and threatens the stall margin. Considering that even applying an end wall suction of the boundary layer has been reported to increase the loss of main flow [28], the side effect mentioned above should be regarded as a common limitation for all the end wall flow control techniques. The blade row's sensitivity to throttling determines whether or not the loss will increase and how much it will increase. So, for the LM point of the current study, the efficiency reduction reflects that the effect of the end wall contouring was limited by the characteristics of the current compressor stator. The problem may be solved by improving the blade profile.  
Above all, the numerical and experimental results indicate that when applying the newly developed end wall contouring method, the intended control of secondary flow in the design space agrees with its actual effect and effectively suppresses the corner separation under multiple inflow conditions. Thus, the results prove its effectiveness. If looking at the empirical end wall contouring method in previously reported studies, the traditional empirical method typically constructs the full area of the end wall surface uniformly through a single analytical formula [2; 7; 8] or by manual adjustment [9]. Incomparison, the newly developed method enables the parametric end wall to control secondary flow in more than one local region under multi-operating conditions. Thus, the control of secondary flow will be more adaptable to different compressors and produce a much closer result to the optimization design, with a relatively small number of design variables. Moreover, in the current new empirical method, the design variables show not only an intuitive effect on the geometry but also a clear relation with the movement of the secondary flow. The new method is thus more convenient for concluding the design experience and shows a possibility to be applied in an optimization process.