Improvement of the effectiveness of spillway operation of high-head hydroelectric stations

Conclusions

• 1. The distance of deflection of a high-head aerated flow being discharged from spillways decreases in proportion to the increase of energy expenditures on compression of the air being compressed by the flow on the ski-jump, where its inertial pressure exceeds the weight pressure by an order of magnitude. For estimating energy losses during discharge of a high-head aerated flow, degree of its deceleration, calculation of the inertial pressure on the ski-jump, and energy exchange between its phases, a constant parameter is proposed, which accurately characterizes the initial index of the flow expressed by the ratio of the mass of water and of the air present in it and which does not depend on external conditions and flow regimes on the ski-jump.

• 2. Cavitation on the spillway face of the dam can be effectively eliminated by increasin the depth of the flow being discharged, in which case the weight pressure of the jet on the surface of the spillway increases (without admission of air under the jet).

• 3. For increasing the unit discharges without additional strengthening and deepening of the structures for dissipating the energy of the flow in the lower pool of the hydro develop ment it is necessary to preliminarily separate the flow being discharged into two or three jets directly within the spillway face of the dam, to restructure appropriately their flow relative to one another in plan and over the height, and to join the components of the flow with the lower pool by mutually different regimes one after the other at a different distance from the dam. For this purpose all components of the flow after their formation initially continue to move parallel relative to one another, then its extreme components are deflected upward from the spillway face for organizing the three-layer flow, and then the width of each layer partially increases, including up to the complete width of the spillway face of the dam: on the end zone they are arranged one above the other at different elevations and join the lower pool each independently in different regimes, which provides the best dissipation of energy and a marked decrease of the effect of the force of the flows being discharged on the river channel and banks.

• 4. Separation of the flow in the exit zone leads to a reduction of the losses of energy on compression of the air contained in the aerated flow, increase of the distance of deflection of the jet, and substantial reduction of the volume of the vapor-air cloud above the flow being discharged.

• 5. The given method makes it possible to take into account the characteristics of the behavior of a two-phase mixture of the flow being discharged and to more reliably estimate the parameters and distance of deflection of the jet.

• 6. The elements separating the flow for reducing the effect of the force on the channel and dissipators can be placed just as at the exit from tunnels.