Hydraulic investigations of antiwhirl dissipator of operating spillway of the Tel'mamsk hydroelectric plant

Abstract

1. The substantial characteristic of the flow regime in an antiwhirl dissipator (AWD) is the presence in it of a region of significant dimensions, the pressure in which reaches the limit of the physically possible vacuum under these conditions, that is, the vaporization pressure. 2. Supply of air in the quantity required for elimination under these conditions of the risk of development of cavitation (taking into account the pressure pulsations) substantially reduces the effectiveness of the AWD as an energy dissipator. 3. The air flow required for protection against intense cativation erosion of a series of AWD zones should be limited by the discharge capacity of the air-feed system, characterized by the value μw=1.2 m2. In this case the averaged pressure drop in the air conduit may reach 6–7 m of water column, which corresponds to a supersonic velocity (about 400 m/sec, that is, more than five times the value usually permitted for aeration shafts). Under such velocities gasodynamic effects are possible (compression jumps, decrease of the discharge capacity, strong sonic phenomena), which call for special investigations. 4. Supply of air under the above conditions may substantially reduce (by a factor of 10) the cavitation erosion intensity, but this does not eliminate it completely, which requires the use of special steel for the liner and, despite this solution, periodic repairs. 5. Hydrodynamic actions on AWD structures are characterized by a pressure pulsation standard, the maximum value of which reaches 180 kPa. Air supply to the AWD does not exert a substantial effect on the hydrodynamic action intensity. 6. It is no permissible to use an AWS for passage of discharges smaller than the design value, to avoid intense cavitation erosion and dangerous dynamic action, including adverse effects on the tunnel portion leading to the AWD. 7. Taking into account the above considerations for favorable technical\3-economic and production indices in comparison with dissipator alternatives under the conditions of the Tel'mamsk hydroelectric plant, use of an AWD can be accepted only in conjunction with another spillway (for example, with a chute) allowing regulation of the overflow discharge.