Abstract: Differences exist between the prototype machine at a tubular power station and its model machine, often leading to an incorrect on-cam operation relationship of the guide vanes and runner blades. This could cause many power stations after being put into operation to suffer from insufficient output and severe vibration. However, adjusting the on-cam operation through on-site prototype experiments is time-consuming and labor-intensive. In this work, numerical optimization of the on-cam operation of a prototype tubular turbine is studied using the dynamic grid technology, considering the effect of free surface and water gravity. The results show that before and after the optimization in low head conditions, the turbine has a wider range of variations in on-cam operation, and its efficiency is more sensitive to changes in guide vane opening. Therefore, for a hydropower station under low head conditions during the wet season, an on-cam operation adjustment is more necessary, and numerical simulations of the optimization is of greater significance. An adjustment to on-cam operation usually imposes a significant impact on the flow regime in the runner near the hub, and a good one will cause an increase in the relative flow angle and a decrease in the positive circular rector at the outlet of the runner near the hub. This brings about a significant improvement in the distribution of backflows and vortex belts in the draft tube, thereby reducing hydraulic loss in the draft tube and raising hydraulic efficiency of the tubular turbine. Thus, numerical optimization of on-cam operation is a useful guide for the design and field test of tubular units.

Key words: tubular turbine, optimization of on-cam operation, dynamic grid technology, free surface, flow regime, efficiency