Untersuchung des Kavitationsbeginns an einer natürlichen körnigen Betonoberflächenrauhigkeit

Abstract

The results of theoretical and experimental studies are described on the conditions of cavitation onset on natural granular irregularities of a concrete surface. It is shown that the value of critical cavitation parameter for an isolated stone (aggregate) on a smooth surface is dependent on the stone shape only with a proper choice of characteristic velocity and pressure. If a stone is among similiar stones, i.e. under real roughness conditions, the effect of neighbouring stones is doubling on it. In the first place, the velocity distribution curve in the approach section is abruptly transformed due to the bottom layer development, thereby decreasing the run-up velocity on the stone. In the second place, the bottom stone is subjected to a vortex wake formed by the flow passing stones located in front of it. Hence, the run-up velocity on the stone decreases even more, and the turbulence of the run-up flow increases. To take into account the above mentioned effects, a shadow function is introduced. Simple relations are given for calculation of cavitation onset on natural granular irregularities of different form and dimensions under differing hydraulic conditions.