# Analysis of the Guide Vane Jet-Vortex Flow and the Induced Noise in a Prototype Pump-Turbine
## 6 Conclusions  
According to the studies above, conclusions can be drawn as follows:  
1. In a pump-turbine's start-up process in pump mode, flow regime is undesirable due to a small guide vane opening angle. In this study at \(C_{\varphi}=0.015\) and \(\alpha=3\) degrees, the jet-vortex flow structure can be observed in the diffuser, including the guide vane, stay vane, and volute. It consists of I--the flow ring between the runner trailing-edge and the guide vane, II--the guide vane jet, III and IV--the twin-vortexes adjacent to guide vane jet, V--the inter stay vane vortex, VI --the stay vane jet, and VII--the volute vortex-ring. These jets and vortexes interfere with the runner pumping and cause an instability of the flow field. 2. Based on the acoustic analogy method, strong noise can be found in the jet-vortex flow structure. Results show that the high turbulence kinetic energy and eddy dissipation caused by undesirable flow structures could be the reason why noise is generated in the flow passages. High sound power level \(L_{sp}\) regions in the jets and vortexes are caused by high turbulence kinetic energy. High \(L_{sp}\) regions on the blade leading-edges are due to local flow striking and separation with strong eddy dissipation. The strongest \(L_{sp}\) region is in the guide vane jet, where \(L_{sp}\) is up to about 150 dB. This shows that the guide vane opening and direction are the most important factors in inducing noise, especially at small guide vane opening angle conditions. 3. The pulsation of turbulence kinetic energy coefficient \(C_{k}\) was studied on monitoring points \(P_{1}\) to \(P_{7}\). Three specific frequencies were found, including the runner blade frequency \(f_{b}=64.5\) Hz, the dominate frequency in the guide vane and stay vane \(f_{gsv}=9.6\) Hz, and the dominate frequency in the volute \(f_{vl}=3.2\) Hz. The \(18\times 18\) flow pulsation tracing topology gives a better visualization of frequency distribution and propagation. The frequency-dominated turbulence kinetic energy coefficient \(C_{k}^{*}\) was used instead of \(C_{k}\) to exclude the pulsation amplitude difference. Results show that different specific frequencies are caused by different flow structures. Frequencies will propagate and affect the adjacent regions. Generally, the guide vane opening angle is found crucial in producing flow noise and turbulence pulsations, especially in the pump mode's start-up process. A better understanding of the flow regime at the small guide vane opening can help reducing and optimizing the flow noise in the future researches. In this study, the numerical study was done on a prototype scale, but the experimental study was conducted on a model scale. In the future, the tests will be done on a prototype pump-turbine unit to have a better comparative analyses. Figure 23: Checking the blending function of the Detached Eddy Simulation (DES) on S\({}_{\rm A}\) and in the specific region on S\({}_{\rm B}\). **Funding:** This research was funded by China Postdoctoral Science Foundation, grant number 2018M640126 and National Natural Science Foundation of China, grant number 51439002. The APC was funded by China Postdoctoral Science Foundation, grant number 2018M640126. **Acknowledgments:** The authors would acknowledge [PERSON] and [PERSON] in China Agricultural University for their supports given during this research. **Conflicts of Interest:** The authors declare no conflict of interest. **Nomenclature**  
**Latin letters**  
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