Cavitation Erosion Intensity Research Articles

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

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.

Basic Study of Coupled Damage Caused by Silt Abrasion and Cavitation Erosion. 2nd Report. Experiments with Water Channel.

Damage due to the coupled action of silts abrasion and cavitation erosion was experimentally studied using water channel in which artificial silt (Al2O3) were included. It was confirmed that the incipient cavitation number in silt laden water increased by 10-15% compared with that in tap water. It was shown that the magnitude of impact pressure measured by the pressure detecting films and casing vibration-acceleration had good correlation with the cavitation erosion intensity but not with the abrasive wear intensity. The damage patterns on aluminum specimens were greatly affected by the cavitation occurrence, but the amount of damaged volume was almost constant with and without cavitation. A ploughing type of abrasive wear was mainly observed on the damaged surface by scanning electron microscope.

Experience of on-site investigations of the cavitation erosion of hydraulic turbines

1. During the first years of operation of the turbines of the Ust'-Ilim hydrostation (1974–1979) increased cavitation erosion of the runner blades were noted. Blades with a maximum deviation of the geometry from the design had maximum erosion. Correction of the blade profile with the use of a three-dimensional template markedly reduced the intensity of cavitation erosion. 2. Tests established that the best operating regimes of the units of the Ust'-Ilim hydrostation with respect to cavitation conditions is the load range 195–215 mW, deviations from which lead to a pronounced increase of cavitation erosion. 3. A change in the profile of the trailing edges of the runner blades practically completely eliminated cavitation erosion on the rear surface of the blades near the trailing edges. 4. Tests with hard-facing of the damaged blades by various electrodes showed the possibility of a substantial increase of the cavitation resistance of the hard-faced coating and accordingly an increase of the overhaul period with the use of electrodes of type TsN-22. It is required to organize immediately the production of cavitation-resistant electrodes, which are acutely needed for restoring cavitation damages of turbine runners.

Static-pressure dependence of the cavitation erosion intensity in liquid oxygen

This study aims to investigate the structural behavior and failure modes of fiber-reinforced-polymer (FRP) confined concrete wrapped with different FRP arrangements. A total of twenty four specimens were cast and tested, with three of these specimens acting as reference specimens and the remaining specimens wrapped with different types of FRP (CFRP and GFRP) by different wrapping arrangements. They include fully wrapped, partially wrapped and non-uniformly wrapped concrete cylinders. The non-uniformly wrapped concrete cylinders provided higher compressive strengths and strain for FRP-confined concrete, in comparison with conventional fully wrapping arrangements. The effect of confinement level on the effectiveness of FRP confinement is also investigated. In addition, the partially wrapping arrangements changes the failure modes of the specimens and the angle of the failure surface.

Conditions of intensity of cavitation erosion. (in Russian) : K. K. Shal'nev. Izvestiia Akademii Nauk SSSR, Otdelenie Teknicheskikh Nauk, 1956, no. 1, Jan. 1956, p. 3–20 + 6 plates

Conditions of intensity of cavitation erosion. (in Russian) : K. K. Shal'nev. Izvestiia Akademii Nauk SSSR, Otdelenie Teknicheskikh Nauk, 1956, no. 1, Jan. 1956, p. 3–20 + 6 plates