Haoqing Jiang

The centrifugal pump is an important component of pumped storage power stations, but the axial force on the impeller significantly affects their stability. Hence, this study focuses on the IS80-65-160 centrifugal pump model and employs Dynamic Mode Decomposition (DMD) to analyze the flow field decomposition of the impeller’s axial forces at three operating points: 1.0nr–1.0Qr, 1.0nr–0.4Qr, and 0.4nr–0.4Qr. The results indicate that DMD can decouple the axial forces on the impeller and extract the temporal mono-frequency coherent structure features and their changes corresponding to the main modes of axial forces, with a nearly zero decay rate and stable periodic vibrations. The first four modes of axial force account for 99.7% of the total modal energy, with the average flow field (mode 0) containing the most flow energy and having the greatest impact on the flow field, The impeller vibrations caused by axial forces mainly occur at the impeller outlet. Modes 1 to 4 of the flow field exhibit similar periodic anti-symmetric coherent structures. At the design speed, the flow field structure is dominated by shaft frequency, but this influence significantly decreases when the speed deviates from the design speed. The findings of this study can help enhance centrifugal pump stability.

In order to improve the hydraulic performance and operational stability of centrifugal pumps, this paper selects M192-400 centrifugal pumps as the research object to ensure that the centrifugal pump head, efficiency does not decrease and reduce the axial force as much as possible as the optimization goal, using the Plackett–Burman screening test will be centrifugal pump impeller balance hole diameter, radial position, circumferential position, and axial placement angle of four geometric parameters as optimization variables. The optimal Latin hypercubic sampling method was used to create a sample space of 90 groups, and the optimization variables were fitted to the optimization targets using the extreme learning machine. Multi-objective optimization is carried out by the Adaptive Non-dominated Sorting Genetic Algorithms III, and the optimal solutions of impeller balance hole diameter, radial position, circumferential position, and axial placement angle of 14 mm, 68.08 mm, −22°, and 6.62° are obtained by using the hierarchical analysis method and the validity of which is verified. Compared with the initial model, the optimized centrifugal pump increased head by 1.28%, increased efficiency by 0.17%, and reduced axial force by 96.47% to meet the optimization target. Before and after the optimization of the centrifugal pump wall pressure, cross-sectional pressure, velocity, and flow lines, turbulent kinetic energy distribution differences were analyzed. The optimization method of this paper makes the centrifugal pump hydraulic performance improved, the basic balance of the axial force, for the centrifugal pump optimization design to provide a reference basis.

In order to study the evolution mechanism of axial force characteristics of centrifugal pump in the transient process of variable working conditions, the IS80-65-160 centrifugal pump is taken as the research object, and four flow operating points of centrifugal pump 1.0Qr, 0.8Qr, 0.6Qr, and 0.4Qr are selected. Non-constant numerical simulation is carried out, and on the basis that the numerical calculation results of the external characteristics are basically consistent with the experimental results, the changes of the axial force of the impeller during the flow reduction process of the variable valve adjustment and the variable speed adjustment of the centrifugal pump are studied, respectively. The results show that as the flow rate decreases, the force of the variable valve regulating impeller cover plate increases, and the force of the variable speed regulating cover plate decreases. Under the two adjustment methods, the axial force on the pressure surface of the blade becomes smaller, the axial force on the suction surface of the blade is basically unchanged, and the pulsation coefficient of the impeller axial force increases first and then decreases. The axial force pulsation coefficient reaches the maximum value in the variable valve adjustment condition of 0.8Qr and the variable speed adjustment condition of 0.6Qr, respectively, and the axial force on the outer wall of impeller cover plate has the greatest influence on the main frequency axial force ripple coefficient; the axial force acting on the outer wall surface of the front cover plate of the impeller and the inner wall surface of the front and rear cover plates increases with the increase in the radius, The axial force acting on the outer wall surface of the rear cover plate of the impeller has axisymmetrical properties. This study revealed the evolution mechanism of the axial force characteristics of the centrifugal pump impeller during the transient process of variable working conditions, and the research results can provide a reference for improving the stable operation of the centrifugal pump.

This study analyzes the transient axial force of a centrifugal pump under variable operating conditions using wavelet analysis and a novel technique called windowed multi-resolution dynamic mode decomposition (wmrDMD). Numerically simulating the sampled time series allows the reconstruction of the impeller’s axial force information, providing validation for this innovative data-driven analysis technique. The comparison between the reconstructed results and the original axial force data demonstrates a remarkable agreement, as all data points exhibit error values below 2.49%. The wmrDMD technique systematically decomposes the impeller’s axial force field into dynamically significant modes across various time scales. Removing the mean flow field in this study resolves the transient motion of the impeller’s axial force, facilitating the identification of positions with high-frequency axial force oscillations and fluctuations in intensity amplitude. The high-frequency axial force of the impeller exhibits stable periodic variations within the operating range of 1.0n_r-1.0Q_r, whereas the changes are insignificant within the range of 0.4n_r-0.4Q_r. However, within the operating range of 1.0n_r-0.4Q_r, both the position and intensity amplitude of the axial force exhibit significant variations without a stable trend. Furthermore, cross-wavelet and wavelet coherence analyses reveal that within the operating range of 0.4n_r-0.4Q_r, the axial forces on the front and rear cover plates show the strongest correlation at the periodic scale. Within the operating range of 1.0n_r-1.0Q_r, the next highest correlation is observed, whereas the correlation is lowest within the 1.0n_r-0.4Q_r operating range.

This paper studies the flow characteristics and disk friction loss of the rear chamber in a centrifugal pump at a design flow condition with six values of the balance holes at diameters from 0 to 12 mm. The results show that the turbulent boundary layer in the rear chamber is greatly affected by the leakage flow. When the balance hole diameter increases, the flow characteristics of the rear chamber is mainly restricted by the mainstream flow field of the volute. However, when the balance hole diameter is larger than the design value, the disk friction loss of the rear chamber remains basically unchanged. On the contrary, when the balance hole diameter is smaller than the design value, the larger the balance hole diameter the smaller the friction loss of the disk in the rear chamber area. The results of this paper provide a reference for reducing axial force and stable operation of a centrifugal pump.