# The Investigation of a New End Wall Contouring Method for Axial Compressors
## 4 Experiment on the Axial Compressor Test Rig
### The Baseline Compressor Stage and the Design of End Wall Contouring  
The compressor of the test rig is a single-stage high-speed axial flow compressor from Northwestern Polytechnic University, as sketched in Figure 12a. The testing stations for the total pressure of the compressor flow field are also illustrated. The diameter of the rotor is 298 mm, with a design speed of 15,200 rpm. Experimental and numerical research on this stage confirmed that when the rotor speeds up to 70% of the design speed, the rotation will reach a relatively steady state for the stator testing, and there will be a considerable corner separation in the casing end wall region of its stator, as shown in the oil-flow photos in Figure 12b. The experiment thus designs end wall contouring on the casing of the stator to improve the performance of the compressor operating at 70% speed. According to the numerical results in the cascade, constructing a concave surface in the front SS corner would raise the pressure gradient and negatively affect the initiation of corner separation, especially when the incidence increases. Therefore, the new design shows an improvement and adopts three units, with the parameters shown in Table 4. The first unit is to suppress the end wall second flow. Here, we use a localized unit with a large profiling area instead of a full-area unit to prevent aggravating the reverse flow in the front SS corner. Its design parameter is listed in the first place of each blank, i.e., \(\varepsilon_{1}=0.2\), \(\varepsilon_{2}=0.7\), \(\xi_{1}=0.5\), \(\xi_{2}=1\), and \(w_{1}=-0.25\). The second localized unit aims to accelerate the secondary climbing flow in the rear part of the SS corner, so the pitch-wise range of the second localized unit is limited to 15% of the circumferential width of the passage (defined with \(w\)) beyond the SS in the rear half of the SS. The third localized unit aims to reduce the potential negative effect in the front SS corner area. The range of this unit thus spreads within 30% \(w\) from the SS, forming a mild upslope surface to reduce the sinking end wall due to the first localized unit. Figure 13 shows the geometry of the end wall contouring and the photo of the experimental part. Figure 12: The compressor stage for the experiment. (**a**) Test rig: (**b**) Oil-flow in the corner region of casing end wall captured at 70% design speed (top: peak-efficiency point; bottom: near-stall point). Figure 15 selects two specific working points and compares the stators' circumferential averaged total pressure loss before and after end wall contouring. One is the working point with the minimum stator loss (\(\overline{m}\) = 0.89). Herein, it is termed the best-matching point for brevity, abbreviated as \"BM.\" Another is a working point during the throttling process (\(\overline{m}\) = 0.77), closer to the near-stall point but still relatively stable for the experiment. It is termed the left-map working point in the following passage, abbreviated as \"LM.\" At the LM point, the variation of \(\sigma\) indicates the overall total pressure loss increases by 1.95% of its original value. At the BM point, the end wall contouring shows a noticeable effect on reducing end wall loss. According to the experimental data in Figure 15a, the total pressure loss coefficient decreases by about 0.01 from 0.7_span_ to the blade tip and nearly remains the same in other regions. The reduction of the total pressure loss reaches 0.035 above 0.9_span_ and 0.01-0.013 from 0.8_span_ to 0.9_span_. The two-dimensional distribution of \(\sigma\) in the outlet plane of the stator is given in Figure 16a,b. This reveals that the low value of \(\sigma\) significantly reduces and moves farther away from the end wall than the baseline stator. This is apparently consistent with the mechanism in the cascade and previous research [4,9]. Figure 14: The overall performance of the compressor stage at 70% design speed.