Insufficient understanding the influence of impeller inlet width on the performance of hydraulic turbine is a problem encountered in the hydraulic turbine design.To perform experimental research on a single-stage centrifugal hydrulic turbine,an open hydraulic turbine test bed was built.Through experimental research a typical performance curve of hydraulic turbine is acquired.Numerical calculation and analysis was done by adopting all flow field and structural mesh technique.Through numerical and expermental comparison,the accuracy of numerical calculation is proved.The results of numerical calculation with different impeller inlet widths show that the increase of impeller inlet was width could offset its best efficiency point(BEP) to large capacity and its efficiency increase gradually at large flow rate;however its influence on efficiency varies at small flow rate.Also it is observed that there is an optimal impeller inlet width for a certain geometric parameters combination of a turbine.The Q-H curve becomes more flat with the increase of impeller inlet width and its shaft power varies at a relaivaly minor amount.
Radial force in low-head axial flow turbines (AFTs) is an influential factor in their operational stability. To explore the transient operating behavior of the radial force in low-head AFTs under different blade numbers, transient numeric computations were executed with the shear stress transport (SST) k-w turbulent model. Turbine performance was numerically computed and compared with results from experiments. Furthermore, the unsteady flow field pulsations were experimentally verified by means of pressure sensors. The radial forces on the runners (z = 2, 3, and 4) were each numerically studied in time, frequency, and joint time–frequency fields. The result reveals that the radial force acting on the runner varies with time, since periodic radial forces reflect the vane number on the stay vanes with minimal runner effect. Moreover, the amplitude of the radial forces is directly proportional to the flow rate. Furthermore, the spectral analysis shows that the radial force frequency is close to the blade passing frequency and also increases radially outward since peak values were recorded in this region. Minimal radial force amplitudes were recorded when z = 3, across all flow conditions, making this configuration suitable for smooth and reliable operation. The unstable pressure and force pulses that affect the noise and vibration produced in the turbine are instigated by the flow exchange that occurs between the guide vane and the runner. In order to optimize turbines for increased operational dependability, the acquired data would be crucial references for noise and vibration analytical investigations.
A numerical comparison of a conventional pump in pump and pump as turbine (PAT) mode is presented. The numerical simulation is carried out with ANSYS CFX software by means of steady state analysis. Through CFD analysis, the relationship of two modes’ performance characteristics, volumetric efficiency, axial thrust and flow field distribution and etc. were acquired. The possible direction for optimization of PAT is clear according to the PAT flow field distribution.
Volute is an important hydraulic part of centrifugal pump, hydraulic loss within pump volute takes up a large part of total hydraulic loss within pump, thus appropriate design of pump volute has significant meaning to centrifugal pump performance. In this paper, numerical method was adopted to investigate volute main geometric parameters, including volute throat area, volute cross-section shape, design rule of spiral development area, and radial gap between impeller and volute tongue to pump performance. A design method of high-efficiency pump volute is developed through the influence of volute main geometric parameters to pump performance. This paper could provide theoretical guidance to high-efficiency pump volute design.
A reserved running centrifugal pump can work as a hydraulic turbine with its wide application in industrial energy recovery and the development of micro-hydraulic power. In order to improve the efficiency from the point of turbine working condition, the impeller with forward-curved blades was designed and the hydraulic performances were further analyzed based on the commercial software ANSYS CFX 12.0 in this study. Moreover, to improve the computational accuracy of numerical simulations on turbines, the grid number, the turbulence model, the circumferential flow distribution in the clearance between the volute and the impeller as well as the grid distribution in the boundary layer were considered. According grid independency analysis, the 1.2 million grids’ number was assumed for numerical simulations. Considering the consuming time and computational stability, as well as the accuracy of the CFD calculation, the k–ε turbulence model was chosen for further calculations. The shaft power and the efficiency of the turbine were more close to the experimental data as the whole computational flow domain in the clearance between the volute and the impeller was connected on the impeller domain. Compared with the performance curves with or without grids in the boundary layer, the boundary layer with grids used in the PAT during numerical simulations was more close to the experimental one. Compared with the experimental data, the H-Q curves of the hydraulic performances of the turbine with forward-curved blades predicted by CFD were positioned under the experimental one. With respect to the efficiency of the turbine, the various ranges of the efficiency is less than 5%, even there is some deviations between the CFD and experimental results. Therefore, the good agreement of the hydraulic performances between CFD and experimental results in present study indicates that the proposed numerical methods can adequately capture the internal flow in a hydraulic turbine with forward-curved blades, and can also provide a reliable reference for the design of hydraulic turbines.
A pump is not ideally designed to operate as a turbine. To improve the efficiency of a pump as turbine (PAT), the redesign of the PAT, according to the flow of the turbine, is required. The blade wrap angle is one of the main geometric parameters in impeller design. Therefore, an investigation into the blade wrap angle to the PAT’s influence can be useful. In order to understand blade wrap angle to the influence of the PAT, this paper numerically investigated three different specific speeds of PATs with different blade wrap angles. The validity of numerical simulation was first confirmed through a comparison between numerical and experimental results. The performance change of the PATs with the blade wrap angle was acquired. A detailed hydraulic loss distribution and a theoretical analysis were performed to investigate the reasons for performance changes caused by the blade wrap angle. The results show that there is an optimal blade wrap angle for a PAT to achieve the highest efficiency and the optimal blade wrap angle decreases with an increasing specific speed. A performance analysis shows the PAT’s flow versus pressure head (Q-H) and flow versus generated shaft power (Q-P) curves are lowered with the decrease of the blade wrap angle. The hydraulic loss distribution and theoretical analysis illustrate that it is the decrease of hydraulic loss within the impeller, together with the decrease of the theoretical head, that results in the performance decrease. The decrease of hydraulic loss within the impeller is attributed to the shortened impeller blade passage and the reduced velocity gradient within the impeller flow channel. With the decrease of the blade wrap angle, the slip factor of the PAT’s impeller is decreased; therefore, its theoretical head is also decreased.
Centrifugal pumps can be operated in reverse as small hydropower recovery turbines and are cheaper than bespoke turbines due to their ease of manufacture. Splitter blades technique is one of the techniques used in flow field optimization and performance enhancement of rotating machinery. To understand the effects of splitter blades to the steady and unsteady influence of PAT, numerical research was performed. 3D Navier-Stokes solver CFX was used in the performance prediction and analysis of PAT’s performance. Results show that splitter blades have a positive impact on PAT’s performance. With the increase of splitter blades, its required pressure head is dropped and its efficiency is increased. Unsteady pressure field analysis and comparison show that the unsteady pressure field within PAT is improved when splitter blades are added to impeller flow passage. To verify the accuracy of numerical prediction methods, an open PAT test rig was built at Jiangsu University. The PAT was manufactured and tested. Comparison between experimental and numerical results shows that the discrepancy between numerical and experimental results is acceptable. CFD can be used in the performance prediction and optimization of PAT.
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