Numerical Simulation in Micro Positive Displacement Turbine and Development of Low Fluctuation Turbine

In order to extract micro hydropower in the very low specific speed range, a Positive Displacement Turbine (PDT) was proposed and steady performances was determined experimentally, however the suppression of large pressure fluctuation is inevitable for practical application of PDT. The objective of the present study is to reveal the mechanism and the characteristics of pressure fluctuation in PDT by use of CFD and to suppress the pressure fluctuation. Unsteady CFD analysis has revealed that large pressure fluctuation is caused by large variation of rotational speed of driven rotor, while the output rotor keeps constant speed. Here is newly proposed a 4-robe helical type runner which can reduce the pressure fluctuation drastically and the performance prediction of new PDT is determined.