# Flow Control of Radial Inlet Chamber and Downstream Effects on a Centrifugal Compressor Stage
## 4 Performance Improvement and Downstream Effects
### Performance of the Radial Inlet Chamber  
Figure 11 shows a comparison of the flow conditions in the original and improved radial inlet chambers under the design conditions. It can be clearly seen that as the geometric parameters \(r_{c}\), \(b_{e}\) and \(w_{e}\) increased, entropy production inside the entire inlet chamber was significantly reduced. Owing to the modifications on the intersection of the intake and spiral channels, the sudden expansion vortices were effectively suppressed at the inlet of the spiral channel, the size and strength of which were significantly reduced together with their influence on the downstream flow. In addition, on the other side of the spiral channel away from the intake, the bottom vortices generated by the improved inlet chamber were also weakened with a lower entropy. Therefore, the flow condition inside the optimized radial inlet chamber was improved, and the flow loss was significantly reduced.  
Detailed distributions of the Mach numbers and entropy at the exit of the spiral channel in the original and improved radial inlet chambers are shown in Figure 12. Compared with the flow pattern in the original one, the average flow speed in the improved structure greatly decreased, and the circumferential flow uniformity of this section increased. Meanwhile, entropy production in the improved spiral channel was much smaller, especially on the right side of this section. This indicates that the modification of the inlet chamber had significantly reduced the flow loss in the spiral channel--especially at the bottom of the  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Item** & **Size** \\ \hline Inlet diameter of intake channel \(D_{in}\) & 460 mm \\ Intersecting width of intake and spiral channels \(w_{e}\) & 996 mm \\ Width of spiral channel \(b_{e}\) & 330 mm \\ Radius of spiral channel \(r_{c}\) & 576 mm \\ Inlet width of annular convergent channel \(b_{l}\) & 220 mm \\ Inlet diameter of annular convergent channel \(D_{l}\) & 440 mm \\ \hline \hline \end{tabular}
\end{table}
Table 4: Geometric parameters of the improved radial inlet chamber.  
Figure 11: 3D flow conditions in the original and improved radial inlet chambers.  
radial inlet chamber away from the intake--and improved the performance of the inlet chamber accordingly. The performance parameters of the original and improved radial inlet chambers have been compared in Table 5.  
In addition, comparisons of the performance parameters under different operating conditions were also performed, as is shown in Figure 13. According to the performance curves of each radial inlet chamber, the total pressure loss coefficient decreased with the increase of the flow rate, and the efficiency of the inlet chamber increased accordingly. Furthermore, it can be clearly observed that the total pressure loss in the improved inlet chamber was significantly reduced under different operating conditions, and the corresponding efficiency was improved as well. By means of the improvement in this paper, the efficiency of the radial inlet chamber increased by 4.97% on average in the entire operating range, and the flow loss decreased by an average of more than 60%, achieving the purpose of improving the performance of the radial inlet chamber itself.  
Figure 12: Flow conditions at the exit of the spiral channel. (**a**) Comparison of Mach numbers. (**b**) Comparison of entropy.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Performance of the Inlet Chamber** & **Original** & **Improved** \\ \hline Efficiency \(\eta_{ic}\) & 89.83\% & 94.86\% \\ Total pressure loss coefficient \(\xi_{ic}\) & 1.1681 & 0.4472 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Performance comparison of the original and improved radial inlet chambers.