Tubular turbine is a type of turbine with low-head. Due to the fact that the runner of a tubular turbine is of axial-flow type, there will be a certain width of blade tip between the blade and the chamber. In order to explore the influence of tip clearance width on the flow inside the turbine, taking the model tubular turbine as the research object, six different tip clearance widths were compared and analyzed. The research shows that the increase in blade tip clearance width affects the performance of the turbine, reduces the minimum pressure at blade tip and causes cavitation in advance. Larger tip clearance width significantly increases pressure pulsation intensity inside the turbine, especially in the vaneless region between the runner and guide vane and the area of the runner tip. However, the increase in tip clearance width can greatly reduce the axial force for about 100 N and radial excitation force for about 50% of rotating parts. Therefore, during the design and processing of tubular turbines, the blade tip clearance width should be carefully selected to ensure safe and stable operation of the unit.

The self-excited vibration of runner is an important factor affecting the stable operation of hydro-turbines. Due to the particularity of structure, there is always a gap between the runner and the shell of the tubular turbine, and the eccentricity of the runner often occurs due to manufacturing or installation. The uneven clearance caused by runner eccentricity will lead to Alford effect and may induce the self-excited vibration. Based on a model tubular turbine, the Alford effect and Alford force of different runner eccentricity is deeply explored through the combination of experiment and numerical simulation. Based on the investigation under a common high-efficiency condition, it is found that the difference of runner eccentricity will cause obvious changes in performance. With the increase of runner eccentricity, the average value of runner radial force increases gradually. The overall frequency of radial force shows several frequency bands and the frequency may shift with the increase of eccentricity level. The runner eccentricity causes obvious changes of internal flow and tip leakage vortex in the blade tip clearances. In the narrowest clearance due to eccentricity, the turbulence kinetic energy and vortex intensity obviously rise up. The pressure in the clearances with different widths are also different. The influence of flow field inside clearance will be the main reason of Alford effect. This study is meaningful for tubular turbines for the operation stability and security.

No abstract