# Aerodynamic and Structural Characteristics of a Centrifugal Compressor Impeller
## 3 Results and Discussion
### Aerodynamic Performance
#### 3.1.2 With Splitter Blades  
The effect of adding splitter blades to the current impeller design is studied and presented in this section. The blade-to-blade view of velocity vectors at 50% span, the meridional contour of entropy, and the circumferential pressure contour distribution at the trailing edge for the different numbers of blade are shown in Figures 8, 9, and 10, respectively.  
The inclusion of splitter blades streamlined the flow after a 50% blade length and prevented the formation of the low-velocity re-circulation region on the pressure side for the six-blade configuration, as shown in Figure 8a. However, small re-circulation formed at the suction side of the splitter blade due to higher flow incidence at the splitter blade leading edge. On increasing the blade number, the flow incidence angle at the splitter leading edge decreased, and the re-circulation region moved downstream.  
The maximum entropy generated was decreased from 136 KJ/kg-K to 130 KJ/kg-K upon the inclusion of splitter blades, as shown in Figures 6 and 9. This maximum entropy region formed at the curvature of the meridional profile for the configuration without the splitter and moved downstream in the splitter configuration. The inclusion of splitter blades decreased the distortion in the circumferential pressure distribution, as shown in Figure 10. This even distribution of circumferential pressure with higher pressure corresponded to the high-pressure rise of splitter configuration. The magnitude of the high pressure region was decreased for the 12-blade configuration, as shown in Figure 10c.  
Figure 4: Performance characteristics.  
Figure 5: Velocity vectors’ 50% span. The re-circulation zone is marked with the dashed circle.  
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Blade \#8**} & \multicolumn{2}{c}{**Blade \#10**} & \multicolumn{2}{c}{**Blade\#12**} \\ \cline{2-7}  & **No Splitter** & **Splitter** & **No Splitter** & **Splitter** & **No Splitter** & **Splitter** \\ \hline Rotation Speed (radian s\({}^{-1}\)) & \(-\)7644.54 & \(-\)7644.54 & \(-\)7644.54 & \(-\)7644.54 & \(-\)7644.54 & \(-\)7644.54 \\ Mass Flow Rate (kg s\({}^{-1}\)) & 0.3000 & 0.3000 & 0.3000 & 0.3000 & 0.3000 & 0.3000 \\ Inlet Volume Flow Rate (m\({}^{3}\) s\({}^{-1}\)) & 0.2361 & 0.2512 & 0.2427 & 0.2536 & 0.2464 & 0.2535 \\ Input Power (W) & 40969.9 & 46516.6 & 43550.8 & 47/486.3 & 45,133.3 & 47,743.9 \\ Work Input Coefficient & 0.6663 & 0.7109 & 0.6892 & 0.7189 & 0.7034 & 0.7230 \\ Total Pressure Ratio & 3.4691 & 3.7317 & 3.5866 & 3.7743 & 3.6542 & 3.7771 \\ Total Temperature Ratio & 1.4897 & 1.5225 & 1.5065 & 1.5284 & 1.5169 & 1.5313 \\ Total Isentropic Efficiency (\%) & 87.8024 & 88.0925 & 87.5507 & 88.0186 & 87.2671 & 87.6186 \\ Total Polytropic Efficiency (\%) & 89.7042 & 90.0684 & 89.5477 & 90.0228 & 89.3419 & 89.6915 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Compressor performance results.  
Figure 8: Velocity vectors’ 50% span, with splitter blade.  
Figure 6: Entropy contour on the meridional surface.  
Figure 7: Pressure contour at the trailing edge.