Load rejection is one of the most crucial transient processes in pump-turbines. However, only a few achievements on the internal flow mechanism of pump-turbines in load rejection processes have been presented. In this...Load rejection is one of the most crucial transient processes in pump-turbines. However, only a few achievements on the internal flow mechanism of pump-turbines in load rejection processes have been presented. In this study, firstly, the load rejection process in a pump-turbine was simulated with a three-dimensional unsteady turbulent numerical method using the technology of dynamic mesh and the user-defined functions in the FLUENT software. The rotational speed predicted through numerical simulation agrees well with experimental data. Secondly, based on numerical simulations, a dynamic instability in the load rejection process was found and presented that the pressure and performance characteristics, including hydraulic torque on the runner and the discharge, fluctuate in the overall trend. Meanwhile, all the performance characteristics and the pressure fluctuate sharply near the operating condition points, where hydraulic torque on the runner is equal to zero or reverse flow is maximum at reverse pump conditions. Finally, the time-frequency features and formation mechanism of the dynamic instability were analyzed emphatically. The analysis of the internal flow in the pump-turbine reveals that dynamic instability in the load rejection process are mainly caused by the vortex flow in the tandem cascades regions. Furthermore, the possible methods to improve the dynamic instability in the load rejection process were recommended.展开更多
In order to explore the unforced unsteadiness of centrifugal pumps,a 2-D frequency domain imaging display technology was used to study the development of these unsteady flow structures at partial flow conditions.The r...In order to explore the unforced unsteadiness of centrifugal pumps,a 2-D frequency domain imaging display technology was used to study the development of these unsteady flow structures at partial flow conditions.The results showed that,the unsteady flow field was not only affected by rotor and stator interaction,but also appeared an unforced unsteadiness with fundamental frequency of St≈0.23 around the impeller throat area.Moreover,as the flow rates decreased,this unsteady flow structure gradually weakened and disappeared.When the flow rate was reduced to 0.6 times of design flow rate,another two unforced unsteady flow structures with characteristic frequencies of St≈0.0714 and St≈0.12 began to appear in the same area.Therefore,with the operating condition smaller than design flow rate,the internal flow became more and more complex.In addition to the forced unsteadiness,the unforced unsteadiness which is not connected with the blade passage frequency became more and more obvious.展开更多
基金supported by Open Fund of Key Laboratory of Fluid and Power Machinery(Xihua Uninversity)Ministry of Education Sichuan(Grant Nos.SZJJ-2017-089 and SZJJ-2017-100-1-001)Open Research Fund Program of State Key Laboratory of Hydroscience and Engineering(Grant No.sklhse-2018-E-02)
文摘Load rejection is one of the most crucial transient processes in pump-turbines. However, only a few achievements on the internal flow mechanism of pump-turbines in load rejection processes have been presented. In this study, firstly, the load rejection process in a pump-turbine was simulated with a three-dimensional unsteady turbulent numerical method using the technology of dynamic mesh and the user-defined functions in the FLUENT software. The rotational speed predicted through numerical simulation agrees well with experimental data. Secondly, based on numerical simulations, a dynamic instability in the load rejection process was found and presented that the pressure and performance characteristics, including hydraulic torque on the runner and the discharge, fluctuate in the overall trend. Meanwhile, all the performance characteristics and the pressure fluctuate sharply near the operating condition points, where hydraulic torque on the runner is equal to zero or reverse flow is maximum at reverse pump conditions. Finally, the time-frequency features and formation mechanism of the dynamic instability were analyzed emphatically. The analysis of the internal flow in the pump-turbine reveals that dynamic instability in the load rejection process are mainly caused by the vortex flow in the tandem cascades regions. Furthermore, the possible methods to improve the dynamic instability in the load rejection process were recommended.
基金supported by the National Natural Science Foundation of China(Grant No.51976125)Open Research Subject of Key Laboratory of Fluid and Power Machinery(Xihua University),Ministry of Education(Grant number zj2015-024)Natural Science Fund of Shanghai(Grant No.19ZR1425900)。
文摘In order to explore the unforced unsteadiness of centrifugal pumps,a 2-D frequency domain imaging display technology was used to study the development of these unsteady flow structures at partial flow conditions.The results showed that,the unsteady flow field was not only affected by rotor and stator interaction,but also appeared an unforced unsteadiness with fundamental frequency of St≈0.23 around the impeller throat area.Moreover,as the flow rates decreased,this unsteady flow structure gradually weakened and disappeared.When the flow rate was reduced to 0.6 times of design flow rate,another two unforced unsteady flow structures with characteristic frequencies of St≈0.0714 and St≈0.12 began to appear in the same area.Therefore,with the operating condition smaller than design flow rate,the internal flow became more and more complex.In addition to the forced unsteadiness,the unforced unsteadiness which is not connected with the blade passage frequency became more and more obvious.
