In remote communities where it is not economical and practically possible to take the grid connection, stand-alone small hydro systems can be used to fulfill the energy requirement Small-scale hydroelectric power systems are emerging as a promising source of renewable energy generation, but they require low cost hydraulic and electric equipments to make them economically feasible In such plants, pumps can be used in turbine mode considering various advantages associated with pump eg ease of availability, proven technology, low initial and maintenance cost, availability for a wide range of heads and flows, etc The efficiency of pump as turbine (PAT) is usually lower than that of conventional hydro turbines However, efficiency is not the primary selection criterion for such machines and it is recommended to operate such machines around maximum efficiency point In the present study, different turbines suitable for micro-hydropower plants are discussed The historical development of PAT is described The review of the state-of-the-art of pump running in turbine mode is presented Different pumps suitable to run in turbine mode for low capacity power generation in micro-hydropower plants as well as in water supply piping systems are discussed Theoretical, experimental and numerical investigations carried out by different researchers on PAT are reviewed The research work on PAT including criteria for selection of pump running as turbine, cavitation analysis, force analysis, loss distribution, various methods of performance enhancement, cost analysis of hydropower plant with conventional hydro turbine and PAT, applications of PAT in water supply pipelines, etc is discussed The worldwide implementation of PAT and different manufacturers of PAT are described The limitations in implementation of PAT as well as the recommendations to improve the performance of PAT are described The current trends and future scope for the further improvement and implementation of PAT are also discussed

Investigations on pump running in turbine mode: A review of the state-of-the-art

Symmetrical and unsymmetrical tip clearances on cavitation performance and radial force of a mixed flow pump as turbine at pump mode

Lucas-Kanade (LK) algorithm, usually used in optical flow filed, has recently received increasing attention from PIV community due to its advanced calculation efficiency by GPU acceleration. Although applications of this algorithm are continuously emerging, a systematic performance evaluation is still lacking. This forms the primary aim of the present work. Three warping schemes in the family of LK algorithm: forward/inverse/symmetric warping, are evaluated in a prototype flow of a hierarchy of multiple two-dimensional vortices. Second-order Newton descent is also considered here. The accuracy & efficiency of all these LK variants are investigated under a large domain of various influential parameters. It is found that the constant displacement constraint, which is a necessary building block for GPU acceleration, is the most critical issue in affecting LK algorithm’s accuracy, which can be somehow ameliorated by using second-order Newton descent. Moreover, symmetric warping outbids the other two warping schemes in accuracy level, robustness to noise, convergence speed and tolerance to displacement gradient, and might be the first choice when applying LK algorithm to PIV measurement.

Evaluating the accuracy performance of Lucas-Kanade algorithm in the circumstance of PIV application

In order to maintain a uniform distribution of pareto-front solutions, a modified NSGA-II algorithm coupled with a dynamic crowding distance (DCD) method is proposed for the multi-objective optimization of a mixed-flow pump impeller. With the pump meridional section fixed, ten variables along the shroud and hub are selected to control the blade load by using a three-dimensional inverse design method. Hydraulic efficiency, along with impeller head, is applied as an optimization objective; and a radial basis neural network (RBNN) is adopted to approximate the objective function with 82 training samples. Local sensitivity analysis shows that decision variables have different impacts on the optimization objectives. Instead of randomly selecting one solution to implement, a technique for ordering preferences by similarity to ideal solution (TOPSIS) is introduced to select the best compromise solution (BCS) from pareto-front sets. The proposed method is applied to optimize the baseline model, i.e. a mixed- flow waterjet pump whose specific speed is 508 min-1·m3s-1·m. The performance of the waterjet pump was experimentally tested. Compared with the baseline model, the optimized impeller has a better hydraulic efficiency of 92% as well as a higher impeller head at the design operation point. Furthermore, the off-design performance is improved with a wider high- efficiency operation range. After optimization, velocity gradients on the suction surface are smoother and flow separations are eliminated at the blade inlet part. Thus, the authors believe the proposed method is helpful for optimizing the mixed-flow pumps.

Multi-objective optimization of a mixed-flow pump impeller using modified NSGA-II algorithm

Particle Image Velocimetry (PIV), pressure and noise measurements are used to study the effect of modifications to tongue and impeller geometries on the flow structure and resulting noise in a centrifugal pump. It is demonstrated that the primary sources of noise are associated with interactions of the non-uniform outflux from the impeller (jet/wake phenomenon) with the tongue. Consequently, significant reduction of noise is achieved by increasing the gap between the tongue and the impeller up to about 20% of the impeller radius. Further increase in the gap affects the performance adversely with minimal impact on the noise level. When the gap is narrow, the primary sources of noise are impingement of the wake on the tip of the tongue, and tongue oscillations when the pressure difference across it is high. At about 20% gap, the entire wake and its associated vorticity trains miss the tongue, and the only (quite weak) effect of nonuniform outflux is the impingement of the jet on the tongue. An attempt is also made to reduce the non-uniformity in outflux from the impeller by inserting short vanes between the blades. They cause reduction in the size of the original wakes, but generate an additional jet/wake phenomenon of their own. Both wakes are weak to a level that their impacts on local pressure fluctuations and noise are insignificant. The only remaining major contributor to noise is tongue oscillations. This effect is shown to be dependent on the stiffness of the tongue.Copyright © 1995 by ASME

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Effect of Modification to Tongue and Impeller Geometry on Unsteady Flow, Pressure Fluctuations and Noise in a Centrifugal Pump

The influences of the four different surface dipole sources in a centrifugal pump on the acoustic calculating accuracy are studied in this paper, by using the CFD combined with the Lighthill acoustic analogy methods. Firstly, the unsteady flow in the pump is solved based on the large eddy simulation method and the pressure pulsations on the four different surfaces are obtained. The four surfaces include the volute surface, the discharge pipe surface, the inner surface of the pump cavity, and the interfaces between the impeller and the stationary parts as well as the outer surface of the impeller. Then, the software Sysnoise is employed to interpolate the pressure fluctuations onto the corresponding surfaces of the acoustic model. The Fast Fourier Transform with a Hanning window is used to analyze the pressure fluctuations and transform them into the surface dipole sources. The direct boundary element method is applied to calculate the noise radiated from the dipole sources. And the predicted sound pressure level is compared with the experimental data. The results show that the pressure fluctuations on the discharge pipe surface and the outer surface of the impeller have little effect on the acoustic simulation results. The pressure pulsations on the inner surface of the pump cavity play an important role in the internal flow and the acoustic simulation. The acoustic calculating error can be reduced by about 7% through considering the effect of the pump cavity. The sound pressure distributions show that the sound pressure level increases with the growing flow rate, with the largest magnitude at the tongue zone.

Numerical and experimental studies of hydraulic noise induced by surface dipole sources in a centrifugal pump

Particle Image Velocimetry (PIV) technology was used to study the unsteady internal flow in a double-blade centrifugal pump (DBCP) impeller at the design flow rate. Relative velocity distributions and turbulence intensity distributions in the DBCP impeller at six phase conditions were obtained. And mean dimensionless relative velocity, turbulence intensity, mean absolute flow angle, mean relative flow angle, mean dynamic pressure and mean angular momentum distributions at the different radii of impeller were calculated. Results show that from impeller inlet to impeller outlet, turbulence intensities gradually decrease. With the increase of radius r, mean dimensionless relative velocity first decreases and then increases, while variation tendencies of mean absolute flow angle and mean dynamic pressure are the opposite. With the increase of radius r, turbulence intensity and mean relative flow angle first decrease, then increase, and then decrease, while mean angular momentum gradually increases.

Experimental investigation of the unsteady flow in a double-blade centrifugal pump impeller

The unsteady flow fields in a centrifugal pump at the shut-off condition (SOC) are simulated by the Unsteady Reynolds Averaged Navier-Stokes (URANS) approach. To improve simulation accuracy and assign the boundary condition, special 3D models are made. Three- -dimensional URANS equations are solved on high-quality unstructured grids with the shear stress transport turbulence model by using the computational fluid dynamics (CFD) code CFX-11.0. Furthermore, the numerical simulation results are validated by particle image velocimetry (PIV) measurements. The main goal of the study is, on one hand, the validation of the numerical procedure proposed, and on the other hand, the detailed analysis of the unsteady inner flow field distribution and pressure fluctuation in the centrifugal pump at SOC. In addition, the head of the pump at SOC is predicted based on CFD results. The flow analysis indicates that there exists two eddies in each impeller flow passage, and the velocity at the volute diffusion part is very low. The amplitudes of pressure fluctuation at $ f_r$ (impeller rotation frequency) and $ 3f_r$ dominate in the impeller, while the pressure fluctuation at $ f_b$ (blade passing frequency) is dominant in the volute.

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Numerical investigation of the inner flow in a centrifugal pump at the shut-off condition

The inner flow analysis of centrifugal pumps has gradually become an important issue for the hydraulic design and performance improvement. Nowadays, CFD simulation toolbox of pump inner flow mainly contains commercial tools and open source tools. There are some defects for commercial CFD software for the numerical simulation of 3-D turbulent internal flow in pump, especially in capturing the flow characteristics under the off-design operating conditions. Additionally, it is difficult for researchers to do further investigation because of the undeclared source. Therefore, an open source software like Open Field Operation and Manipulation (OpenFOAM) is increasingly popular with researchers from all over the world. In this paper, a new computational study was implemented based on the original solver and was used to directly simulate the steady-state inner flow in a double blades pump, with the specific speed is 111. In order to disclose the characteristics deeply, three research schemes were conducted. The ratios (Q/Q
 d
 ) of the flow rate are 0.8, 1.0 and 1.2, respectively. The simulation results were verified with the Particle Imaging Velocimetry (PIV) experimental results, and the numerical calculation results agree well with the experimental data. Meanwhile, the phenomena of flow separation under the off-design operating conditions are well captured by OpenFOAM. The results indicate that OpenFOAM possesses obvious strong predominance in computing the internal flow field of pump. The analysis results can also be used as the basis for the further research and the improvement of centrifugal pump.

Research of inner flow in a double blades pump based on openfoam

Radial diffusers can improve the flow uniformity in pumps and affect the hydraulic performance of centrifugal pumps directly. The diffusion coefficient d is an important parameter in fluid machinery but it has seldom been used in the diffuser design of single-stage centrifugal pumps. To improve the design method of radial diffuser use in centrifugal pumps, the diffusion coefficient was introduced into the design of radial diffusers based on a single-arc hydraulic design method and it was found that the vane outlet angle, vane outlet thickness and vane number have a significant impact on the design results. A single-stage centrifugal pump with a radial diffuser was selected as the research model. The inner flow was simulated using the commercial computational fluid dynamics (CFD) program CFX and verified by experiment. The results indicate that the head and efficiency of the pump are best when the vane outlet angle is 6°. The flow area decreases and the flow velocity at radial diffuser outlet incre...

https://www.tandfonline.com/doi/pdf/10.1080/19942060.2016.1210027

Minggao Tan

Papers

Numerical and experimental studies of hydraulic noise induced by surface dipole sources in a centrifugal pump

Experimental investigation of the unsteady flow in a double-blade centrifugal pump impeller

Numerical investigation of the inner flow in a centrifugal pump at the shut-off condition

Research of inner flow in a double blades pump based on openfoam

Design and analysis of a radial diffuser in a single-stage centrifugal pump