Characterization of the hydraulic performances of perforated plates

Single- and multi-hole orifices are largely used in hydraulic pressurized systems mainly as flow conditioners and energy dissipaters, also because they are able to limit the onset and the development of cavitation phenomena in specific operating conditions. The main hydraulic features of these devices have been widely discussed in literature, with the aim of identifying the most important parameters affecting their performances, both in terms of dissipation efficiency and cavitation occurrence. Although these two issues are strictly connected, most of studies only focus on one of them, due to the significant number of parameters governing the phenomena. In previous studies, it has been identified that both dissipation and cavitation characteristics are significantly affected by geometrical features, such as the equivalent diameter ratio (beta), the dimensionless plate thickness (t/d(h)), and the number (n(h)), disposition and shape of the holes. A substantial influence of operating conditions, mainly summarized through the Reynolds number Re, has been also witnessed. Actually, further research is needed mainly to correctly define and relate the influence of specific parameters on the overall hydraulic performances of these devices. The present study summarizes the results of several experimental campaigns recently carried out at the hydraulic laboratory at Politecnico di Bari. A large number of these devices, characterized by different geometries, were tested in variable flow conditions, and the collected results compared with the most relevant literature findings. Wide ranges of the most influential parameters were covered, and the operating conditions also properly modified. In the paper, considerable attention has been done in quantifying the dependency of the dissipating efficiency of the devices, expressed in terms of the most widely used flow coefficients (e.g. the pressure loss coefficient K or the discharge coefficient C-d), upon the above mentioned parameters. Similarly, cavitation onset and development has been witnessed in specific operating conditions, and the most favorable conditions and configurations also mentioned.