Increasing cavitation in a flowing liquid in a pipe system is associated with increasing levels of sound or noise and vibrations. It can lead to large loads if steam bubbles implode close to the pipe wall, which can be harmful to the pipe system. It can lead to fatigue due to vibrations and even worse, erosion of the pipe wall. In the worst case, it can lead to a pipe break. Therefore, cavitation is essential to be predicted and prevented in system design. The aim here is to experimentally verify a concept for the elimination of strong cavitation and harmful cavitation induced vibrations. It has been experimentally demonstrated that replacing a conventional orifice plate with three stages of multi-hole orifice plates in series with only a total streamwise distance of two pipe diameters, giving the same total pressure drop, is sufficient for the elimination of strong cavitation. The cavitation induced vibration levels are reduced by almost 500%. The streamwise distance is almost 500% shorter if multiple conventional orifice plates were to be employed. The same conclusions hold for tests performed with β = 0.30 and 0.40. This compact design was successfully applied at a nuclear power plant, and the reduction of the cavitation induced vibration levels was confirmed. The main contribution is the quantification of the vibration levels, how they depend on the type of orifice plates (conventional, multi-hole, and multi-stage-multi-hole), and how they scale with the dynamic pressure. This will be used for the validation of future CFD simulations including Fluid Structure Interaction (FSI) and advanced two-phase models.

New experiments have been carried out on the generic case of the flow through orifice plates. The aim has been to validate empirical correlations used for the prediction of cavitation. The new accurate experimental data base shows that earlier proposed empirical correlations work well for the prediction of cavitation, e.g., Tullis (1993), Miller (2009), and Nilsson (2011). Using the present data together with earlier data from Tullis (1993), it has been shown that, at the onset of cavitation, the ratio between the downstream and the upstream pressure over the orifice plate is a simple linear function of the orifice plate diameter ratio, β = d/D. This has been shown to hold independent of flowrate, downstream pressure, orifice diameter (for 0.4 < β < 0.8, which corresponds to a pressure loss coefficient 1 < ξ < 100) and boundary conditions (e.g., upstream pipe bends), at moderate temperatures and as long as the pressure drop is large compared to the saturation pressure. A novel and simple rule-of-thumb for when the cavitation becomes a problem (i.e., in between critical cavitation and incipient damage) has been demonstrated to be when the ratio between the downstream and the upstream pressure over the orifice plate equals the orifice plate diameter ratio.