Channel Theory For High-head Bulb Runner

Because the specific speed of bulb turbine is higher than that of the francis turbine, the discharge and power of bulb turbine are larger when head and the diameter is same. However, for bulb turbine, the discharge is large, the number of runner blades is less, the total area is small, cavitation coefficient is large, Intensity condition is bad, as a result, the application head is limited. To increase the head of bulb turbine, it is necessary to improve the runner blade design method and design high head bulb turbine with good energy and cavitation coefficient performance high.Before the hydraulic design of bulb turbine runner is carried out, it is important to study the actual water flow in bulb turbine in order to choose the geometric parameters of flow channel and correctly draw the shape of the blades. This paper propose the channel theory according to the flow of bulb turbine outlet. The theory ensure no impact of runner blades inlet, analyze the projection geometry of runner blades in the meridional plane, meet requirements of runner outlet by adjusting Euler energy. This approach effectively solved the problem of runner blade angle adjustment and is able to rapidly design Runner blades with good performance.In the course of runner design,the paper investigate the Euler energy distribution of runner by means of drawing the curves of Euler energy changing with blade length, ensure their distribution is more reasonable, circulation of runner outlet is small and the flow of draft tube is smooth. At the same time, it determine a reasonable blade thickness along the camber line,and thicken the blades in order to make blades streamlined. It ensure intensity of blades is sufficient and the distribution of speed and pressure is desired. The hydraulic losses of runner is reduced.For confirming the hydraulic performance of runner, This study numerically simulate the flow of bulb turbine by means of CFD technology, analyze speed and energy distribution of runner in the three operating conditions (design conditions, the optimal conditions, low discharge conditions), study the actual flow situation. In this way, it is concluded that the performance of runner is good and this design method is feasible.Finally, it is found that circulation distribution assumption of guide vane outlet is inconsistent with the analytical results. In order to solve this problem, the circulation distribution assumption is modified according to the actual flow. The optimized design was improve the performance of runner blades.