HYDRAULIC GRADIENT IN FREE SURFACE FLOW ON ROTATING BUCKET OF PELTON TURBINE

摘要

So far, there is no paper that quantitatively investigates the effect of the hydraulic gradient on the unsteady free water sheet flow in the rotating buckets of Pelton turbines. The paper presented the numerical analysis how the hydraulic gradient in the free surface flow affects the flow behavior on a rotating bucket under the various rotating angles. The moving grid algorithm was applied to numerically analyze the distributions of the water depth, the specific hydraulic energy and the hydraulic gradient in the unsteady free water sheet flow on the rotating bucket. The hydraulic gradient was divided into two components: the stream-wise component and the transverse component. If the stream-wise hydraulic gradient (partial deriv E_p)/(partial deriv S) was negative at a grid point, the fluid particle at the point was accelerated, and vise versa. Similarly, the transverse hydraulic gradient (partial deriv E_p)/(partial deriv B) contributed if the fluid particle tends to transversely extend or converge on the curved bucket surface. The paper clarified the effect of the stream-wise and transverse hydraulic gradients on the free water sheet flow in a rotating bucket of Pelton turbines.