Parametric study on the effect of inlet and outlet pipe shape on the flow fluctuation characteristics associated with a positive displacement hydraulic turbine

For applications involving very low specific speeds resulting from very low flow rates with medium to high heads, a special class of hydraulic turbine known as Positive displacement turbine (PDT) is most suited. These turbines are not very common, but they can effectively harness the micro and Pico hydropower. For the presentwork, the effect of inlet and outlet pipe's cross-sectional shape on the fluid flow pulsations and overall performance of the developed PDT has been analyzed using Computational Fluid Dynamics (CFD) approach. Initially, the cross-sectional shape of the pipe used for transporting the working fluid to and from the turbine rotors was circular. Subsequently, the influence of square and rectangular cross-sectional shaped pipe designs was analyzed. Also, parametric studies were performed to find the dimensions of rectangular and variable cross-sectional shaped pipes. It was observed that the initial flow pulsations greatly reduced for specified variable cross-sectional pipe compared to the other shapes. Also, an increment of 0.824% in hydraulic efficiency was observed compared to the initial circular pipe. At the rated conditions, the PDT with twisted rotors having fully circular shaped pipe developed 7.15 kW of output power with a hydraulic efficiency of 66.2% from the experimental study. (C) 2020 Elsevier Ltd. All rights reserved.