Considering the complexity flow characteristics and the rotation curvature effect on the internal unsteady flow in a centrifugal pump, a hybrid Reynolds-averaged Navier–Stokes/large eddy simulations method based on the von Kármán scale and the correction of the rotation curvature has been established, and its effectiveness has also been verified. Proper orthogonal decomposition method is used to study the internal unsteady flow structure in a centrifugal pump for its advantages on turbulence analysis. Further, the complex flow characteristics of the vertical single-stage marine centrifugal pumps have been studied, and the relationship between the energy distribution characteristics of the internal flow structure and hydraulic performance has been explored under different operating conditions. The results show that when the fluid flows into the impeller, which is affected by the angle of attack of the inflow, system rotation, and bending blades, the flow separation occurs and leads to an unstable flow in the impeller. The obvious pressure fluctuations emerge on the blades surface, which affects the energy conversion ability of blades. The poor inflow in the impeller causes the low local pressure could also affect the anti-cavitation ability of the centrifugal pump. In addition, there are multi-scales of the flow structures in the centrifugal pumps, and the energy distribution of flow in the centrifugal pump with good hydraulic performance is more concentrated in low-order and large-scale flows structures, and the high-order and small-scale flow structure contains less energy, which indicates that the energy distribution characteristics of the flow structures could be used as a criterion to evaluate the performance of the centrifugal pump.

Considering the computing accuracy and resources of numerical calculation, a hybrid Reynolds-averaged Navier–Stokes/large-eddy simulations method based on the von Kármán scale and the corrected eddy viscosity has been used to study the unsteady flow structure and pressure pulsation characteristics in a centrifugal pump. The unsteady flow characteristics of the vertical two-stage marine centrifugal pumps with complex structure have been studied. The dynamic mode decomposition method is used to study the internal unsteady flow structure and analyze the mechanism of pressure pulsation in the centrifugal pump. The results show that the unstable flow in impeller is mainly affected by the inflow state, system rotation, and the structure of the impeller. Different inflow states lead to obvious differences of the internal flow states and unsteady flow structures between the first-stage and second-stage impellers. There are complex pressure pulsation characteristics dominated by different frequencies in different parts of a two-stage centrifugal pump. The impeller blade main pass frequency has different causes at different locations in the downstream flow passages. The mutual matching of different numbers of impeller blades and guide vane blades will result in a kind of impeller guide vane blade interaction frequency in guide vane and volute, which will excite higher harmonics of the impeller blade frequency. Other important characteristic frequencies in centrifugal pumps had been analyzed. The pressure pulsation mechanism analysis of the centrifugal pump will help researchers to optimize the design of the centrifugal pump and improve the operation stability of the centrifugal pump. Some possible improvement measures for typical frequency pressure pulsation are recommended.

Through numerical simulation and experiments analysis, it is indicated that the hydraulic and anticavitation performance of a centrifugal pump with twisted gap drainage blades based on flow control theory can be significantly improved under certain operating conditions. In order to introduce the technology of gap drainage to practical applications, we put forward the parameter formulas of the twisted gap drainage blade to design three-dimensional new type blade, which are also proved to be effective for enhancing the dynamic characteristics of the centrifugal pump. Furthermore, a practical centrifugal pump is redesigned to be a twisted gap drainage impeller with the same structure size as the original impeller, and the nonlinear hybrid Reynolds-averaged Navier–Stokes (RANS)/large eddy simulation (LES) method is employed to simulate the hydraulic dynamic characteristics. Numerical simulation results show that the hydraulic performance and dynamic characteristics of the redesigned impeller centrifugal pump are significantly enhanced. In experiments, the twisted gap drainage blades structure not only remarkably improves the hydraulic performance and the pressure pulsation characteristics of the centrifugal pump but also reduces the vibration intensity.

Previous work has shown that the employment of a gap drainage impeller in a centrifugal pump can improve the pump's hydraulic performance and cavitation resistance. However, during experiments, an unconventional cavitation phenomenon has been observed in the form of a staggered pair of fixed impeller flow tunnels. For the purpose of understanding the factors involved with this unconventional phenomenon, the present study analyzes the cavitation formation and evolution processes using numerical and experimental methods. A scalable detached eddy simulation (SDES) method was employed to address unsteady turbulent flow. First, the method was validated by comparing the performance data and liquid water velocity distributions obtained by calculation and experiment in the absence of cavitation. Then, numerical simulations of the cavitation flow field were conducted under a flow discharge condition one-half that of the optimum value. Within a particular range of cavitation numbers, the calculated results are found to reproduce the unconventional cavitation phenomenon observed in the experiments. The formation mechanism involves a combination of many factors such as impeller geometry, inflow discharge condition, and cavitation number. As for a certain geometry, the formation and evolution processes can generally be analyzed and explained according to the influence of the attack angle, which is affected by variations in the allocated flow discharge and cavitation volume in each impeller tunnel. The jet flow through the gap between the main and vice blades also contributes to the formation of this phenomenon.