## 5 Noise Optimization Design of Centrifugal Pumps
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Pump Structures** & **References** & **Key Findings** \\ \hline \multirow{3}{*}{\begin{tabular}{c} Impeller outlet \\ width \\ \end{tabular} } & [112; 113] & \(\bullet\) & The decrease of impeller outlet width weakens the pressure fluctuations intensity and leads to the decrease of vibration and noise. \\ \hline \multirow{3}{*}{\begin{tabular}{c} Impeller diameter \\ \end{tabular} } & \multirow{3}{*}{[32; 85; 114; 115]} & \(\lozenge\) & The decrease of impeller diameter weakens the rotor-stator interaction intensity and realizes the noise reduction, while it has little impact on the directivity characteristics. \\ \cline{1-1}  & & \(\lozenge\) & Critical value for the decrease of impeller diameter exists. The noise reduction effect weakens when the decrease value exceeds the critical value. \\ \hline \multirow{3}{*}{\begin{tabular}{c} Blade outlet angle \\ \end{tabular} } & [102; 116; 117] & \(\bullet\) & The decrease of blade outlet angle weakens the fluctuations intensity of noise source, which results in the noise reduction, while it has little impact on the directivity characteristics. \\ \hline \multirow{3}{*}{\begin{tabular}{c} Blade type \\ \end{tabular} } & \multirow{3}{*}{[74; 79; 118; 119; 120; 121]} & \(\lozenge\) & The impeller with splitter blades affects the dipole directivity characteristics and leads to the noise reduction. \\ \cline{1-1}  & & \(\lozenge\) & The inclined blade layout weakens the vibration intensity and noise amplitude, while it affects little the directivity characteristics. \\ \cline{1-1}  & & \(\lozenge\) & The number of blades has no obvious influence on the vibration and noise. \\ \hline \multirow{3}{*}{\begin{tabular}{c} Vane wrap angle \\ \end{tabular} } & [81; 122] & \(\bullet\) & The change of vane wrap angle has no obvious effect on the vibration intensity and noise. \\ \hline \multirow{3}{*}{\begin{tabular}{c} Blade inlet \\ incidence angle \\ \end{tabular} } & \multirow{3}{*}{[82]} & \(\lozenge\) & The change of blade inlet incidence angle has no obvious impact on the vibration and noise. \\ \cline{1-1}  & & \(\bullet\) & The noise with 316L (one kind of anti-corrosion stainless steel) used as port valve is the largest, followed by the noise with NYLON (Aliphatic polyamides) used as port valve, the third one is the noise with PEEK (Polybretheretherketone) used as port valve and the noise with PTFE (Polytetrafluoroethylene) used as port valve is the lowest. \\ \hline \multirow{3}{*}{\
\begin{tabular}{c} Inlet shape \\ \end{tabular} } & \multirow{3}{*}{[124]} & \(\lozenge\) & The straight inlet shape improves the unsteady fluctuation characteristics inside the pump compared with the pre-rotating inlet shape and leads to the reduction of pressure fluctuations intensity. \\ \hline \multirow{3}{*}{
\begin{tabular}{c} Volute shape \\ \end{tabular} } & \multirow{3}{*}{[125]} & \(\bullet\) & The volute with rectangular cross section has a better noise behavior than that with horseshoe-shaped cross section. \\ \cline{1-1}  & & \(\bullet\) & The noise obtained by volute with round edge cut-water is lower than that obtained by volute with sharp edge cut-water. \\ \hline \hline \end{tabular}  
* Footer: “\(\bullet\)”and “\(\diamond\)” are used to distinguish the passive control results of different pump structures.  
\end{table} 
Table 4: Analysis results of passive control. It is noticeable that the flow-induced noise of centrifugal pumps is affected by various pump structures. On the basis of low flow-induced noise and high hydraulic performance, it is more ideal to explore the effect of various structure combinations on flow-induced noise and hydraulic performance. Then, the optimization algorithm is designed to analyze the influence of various factors on noise and hydraulic performance, as well as the corresponding influence proportion, so that the optimal geometric parameters could be obtained [126; 127; 128; 129; 130]. Predictably the optimization method effectively promotes the optimization development.