Derived Empirical Relationship for Cavitation Analysis on Bulb Turbine in Small Hydro Electric Power Plant Utilizing Plant Sigma

Handling of large powers per unit and yet keeping the size of a turbine economically small requires higher running speeds, which means greater pressure differences between the two sides of the vanes of a runner. If the pressure at any point in the vane reaches the critical pressure for causing cavitation, the vane gets damaged. Cavitation is the formation of holes or voids, in water due to the occurrence of low pressures. This boiling like phenomena occurs at all points in a stream flow where the pressure is as low as the vapour pressure of the liquid. The cavities (bubbles) thus formed are filled up with vapour and move millions for seconds. When they collapse, they collapse with a force greater than that of breaking strength of steel causing a dent in the conduit carrying the flow. Cavitation induces vibrations, damage to the materials, unendurable noise and losses in the efficiency and alteration in flow pattern. Hence, hydraulic machineries have to be designed entirely free from cavitation.