Forecast and provision of cavitation-erosion safety in high-head spillways

Conclusions

• 1. A cavitation-safe layout (design) is one for which the depth of the expected erosion is technically admissible and sufficiently clearly forecastable. In this case we mean by technical admissibility such a situation when for the worst forecast of erosion its extent does not threaten the integrity or bearing capacity of the structural elements and the damaged places can be repaired.

• 2. The occurrence of a vacuum and cavitation upon separation of the flow from the gate, its sill, and grooves is not admissible in a cavitation-safe layout; all such separation zones should be reliably aerated. In the case of attachment of the through-going flow to the walls (bottom) of the gate chamber below the main gate, all excess energy of the wall (bottom) part of the flow which can cause cavitation erosion on “intrinsic” cavitation sources of the linings (joints, welds, waviness and roughness of the surface) should be absorbed by a cavitation-resistant lining and dissipated by it.

After the through-going flow “attached” to the walls (bottom) acquires a direction parallel to them it is expedient to accelerate in every possible way the dissipation of the excess energy of the wall (bottom) part of the flow by creating local separation with aeration of the flow (by means of reverse steps and fins). In the presence on the lining of the minimum admissible local technological irregularities (e.g., weld beads) the lining can be considered safe if it does not lose strength upon the occurrence of cavitation erosion with a depth equal to two heights of the irregularity and four heights of the expected grains of the conditionally unifor (e.g., corrosion) roughness.