In hydropower, the exploitation of small power sources requires the use of small turbines that combine efficiency and economy. Banki-Michell turbines represent a possible choice for their simplicity and for their good efficiency under variable load conditions. Several experimental and numerical tests have already been designed for examining the best geometry and optimal design of cross-flow type machines, but a theoretical framework for a sequential design of the turbine parameters, taking full advantage of recently expanded computational capabilities, is still missing. To this aim, after a review of the available criteria for Banki-Michell parameter design, a novel two-step procedure is described. In the first step, the initial and final blade angles, the outer impeller diameter and the shape of the nozzle are selected using a simple hydrodynamic analysis, based on a very strong simplification of reality. In the second step, the inner diameter, as well as the number of blades and their shape, are selected by testing single options using computational fluid dynamics (CFD) simulations, starting from the suggested literature values. Good efficiency is attained not only for the design discharge, but also for a large range of variability around the design value.

Banki-Michell Optimal Design by Computational Fluid Dynamics Testing and Hydrodynamic Analysis

The paper refers to the numerical analysis of the internal flow in a hydraulic cross-flow turbine type Banki. A 3D-CFD steady state flow simulation has been performed using ANSYS CFX codes. The simulation includes nozzle, runner, shaft, and casing. The turbine has a specific speed of 63 (metric units), an outside runner diameter of 294 mm. Simulations were carried out using a water-air free surface model and k-e turbulence model. The objectives of this study were to analyze the velocity and pressure fields of the cross-flow within the runner and to characterize its performance for different runner speeds. Absolute flow velocity angles are obtained at runner entrance for simulations with and without the runner. Flow recirculation in the runner interblade passages and shocks of the internal cross-flow cause considerable hydraulic losses by which the efficiency of the turbine decreases significantly. The CFD simulations results were compared with experimental data and were consistent with global performance parameters.

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Numerical Investigation of the Internal Flow in a Banki Turbine

Numerical analysis and performance enhancement of a cross-flow hydro turbine

Efficiency is a critical consideration in the design of hydro turbines The crossflow turbine is the cheapest and easiest hydro turbine to manufacture and so is commonly used in remote power systems for developing countries A longstanding problem for practical crossflow turbines is their lower maximum efficiency compared to their more advanced counterparts, such as Pelton and Francis turbines This paper reviews the experimental and computational studies relevant to the design of high efficiency crossflow turbines We concentrate on the studies that have contributed to designs with efficiencies in the range of 88–90% Many recent studies have been conducted on turbines of low maximum efficiency, which we believe is due to misunderstanding of design principles for achieving high efficiencies We synthesize the key results of experimental and computational fluid dynamics studies to highlight the key fundamental design principles for achieving efficiencies of about 90%, as well as future research and development areas to further improve the maximum efficiency The main finding of this review is that the total conversion of head into kinetic energy in the nozzle and the matching of nozzle and runner designs are the two main design requirements for the design of high efficiency turbines

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The Design of High Efficiency Crossflow Hydro Turbines: A Review and Extension

Utility of CFD in the design and performance analysis of hydraulic turbines — A review

Recently, small hydropower attracts attention because of its clean, renewable and abundant energy resources to develop. Therefore, a cross-flow hydraulic turbine is proposed for small hydropower in this study because the turbine has relatively simple structure and high possibility of applying to small hydropower. The purpose of this study is to investigate the effect of the turbine's structural configuration on the performance and internal flow characteristics of the cross-flow turbine model using CFD analysis. The results show that nozzle shape, runner blade angle and runner blade number are closely related to the performance and internal flow of the turbine. Moreover, air layer in the turbine runner plays very important roles of improving the turbine performance.

Performance and Internal Flow Characteristics of a Cross-Flow Hydro Turbine by the Shapes of Nozzle and Runner Blade

In order to improve the performance of cross-flow hydro turbine, detailed examination of the effect of the turbine configuration on the performance is needed necessarily. Therefore, this study is aimed to investigate the effect of blade angle on the performance of the cross-flow hydro turbine. Analysis of the turbine performance with the variation of the blade angle has been made by using a commercial CFD code. The results show that inlet and outlet angles of runner blade give considerable effect on the performance of the turbine. Pressure on the surface of the runner blade changes remarkably by the blade angle both at the Stages 1 and 2. Moreover, relatively small blade inlet angle is effective to produce higher value of output power. Recirculating flow in the runner passage causes remarkable hydraulic loss.

Effect of Blade Angle on the Performance of a Cross-Flow Hydro Turbine

The purpose of this study is both to further optimize the structure of cross-flow turbine and to improve the turbine performance. Optimization of the turbine structure has been made by the analysis of the turbine performance with the variation of the blade angle using a commercial CFD code. The results show that inlet and outlet angles of the runner blade give considerable effect on the performance of the turbine. Pressure on the surface of the runner blade changes considerably with the variation of blade angle both at the stages 1 and 2 but relatively small change occurs for the fluid velocity of cross-flow hydraulic turbine. Recirculating flow in the runner passage causes considerable hydraulic loss by which efficiency of the turbine decreases very much.

CFD Analysis for the Performance of Cross-Flow Hydraulic Turbine with the Variation of Blade Angle

The purpose of this study is to examine the effect of nozzle shape on the performance and internal flow of a cross-flow hydro turbine. CFD analysis for three kinds of nozzle shape is conducted to simulate the effect of nozzle shape. The results reveal that relatively narrow nozzle width is effective to increase the turbine efficiency and output power. Almost output power is achieved at Stage 1. Therefore, optimum design of the nozzle shape is necessary to improve the turbine performance. Recirculation flow in the runner passage decreases the turbine efficiency and output power because the flow make hydraulic loss and collision loss in the region. Air should be put into the runner passage and the recirculating flow should be suppressed by the air layer in the runner.

Effect of Nozzle Shape on the Performance and Internal Flow of a Cross-Flow Hydro Turbine

Performance improvement of Small hydro turbine is a very important subject to solve in the stage of introduction and development of the turbine. Cross-flow hydro turbine should be also studied more in detail for the turbine performance in order to extend the sites of application. In order to improve the turbine performance, the effect of the turbine shape on the turbine performance should be examined. Therefore, the effect of runner blade number on the turbine performance is investigated by use of a commercial CFD code. The results show that runner blade number gives remarkable effect on the efficiency and output power of the turbine. Pressure on the surface of the runner blade changes considerably by the blade number at Stage 1, but relatively small change of velocity distribution occurs in the flow passage.

Jae-Ik Lim

Papers

Performance and Internal Flow Characteristics of a Cross-Flow Hydro Turbine by the Shapes of Nozzle and Runner Blade

Effect of Blade Angle on the Performance of a Cross-Flow Hydro Turbine

CFD Analysis for the Performance of Cross-Flow Hydraulic Turbine with the Variation of Blade Angle

Effect of Nozzle Shape on the Performance and Internal Flow of a Cross-Flow Hydro Turbine

Performance Analysis of a Cross Flow Hydro Turbine by Runner Blade Number