Performance analysis of an undershot cross-flow water turbine based on the flow near the runner

Abstract

Since the great east Japan earthquake in 2011, renewable energy is turned into importance. Hydro power is one of most important energies because it is not affected by weather condition and possible to generate steady quantity electric power, so it could be base load power. These days low head hydro power generation is going to increase, because it is easy to be set irrigation channel and agricultural waterway. We have developed water turbines appropriately for low head open channels to effectively utilize the hydro power energy. To improve the performance of the turbine, it is necessary to determine the free surface flow patterns around the turbine. We selected the undershot cross-flow water turbines which could apply to various sizes of channel and flow rate. Because we removed the turbine casing and guide vane, free surface flow patterns of the undershot cross-flow water turbine are very complex. We have researched free surface flow patterns around the turbines using both experiment and numerical analysis. We modified the apparatus system, and could measure mechanical friction loss of bearing. We introduced more precise computational grid of numerical analysis. So it was possible to specify more precise flow patterns near the runner. Time-averaged velocity distribution at inner or outer circumference of runner was almost consistent. As rotational speed increased, volume of cross-flow decreased and that of reversal flow increased. In generating torque and power of turbine, the most significant kind of flow was second stage cross-flow, and the most dominant component of flow was angular momentum. We estimated the torque and power of the turbine based on moment-of-momentum equation, and these results were consistent well with those of calculation.