Analysis of Pressure Fluctuation of Tubular Turbine under Different Application Heads

The vigorous development of low-head hydraulic resources and tidal energy with greater stability and predictability is drawing attention to tubular turbines. However, many problems, such as incorrect unit association relationship, insufficient unit output, and severe vibration, occur frequently in tubular turbines, particularly when the water head is low. These phenomena cannot be known through model machine tests and numerical studies. Therefore, this study takes the tubular turbine with different water heads as the research object, in accordance with the actual boundary conditions. The unsteady numerical research for the prototype machine is conducted while considering the free surface in the reservoir area and water gravity. The internal flow characteristics of the tubular turbine with different water heads and the influence of free surface on its performance are analyzed. The research indicates the following: affected by the free surface and the water gravity, the pressure in the entire flow passage of the horizontal tubular turbine increases with the increase in the submerged depth. In addition, the short water diversion section allows the water flow from the reservoir area to still have a certain asymmetry before reaching the runner. During the rotation process of the runner, the surface pressure and torque of the blade have evident periodic fluctuations, and the amplitude of the fluctuations will increase significantly with the decrease in H/D₁. Moreover, in the case of small H/D₁, the amplitude of pressure pulsation in the draft tube is larger, and concentrated high-frequency pressure pulsation occurs. These factors will lead to the occurrence of material fatigue damage, unstable output, and increased vibration in low-head tubular turbines.