SCOUR MORPHOLOGY DUE TO VERTICAL CROSSING JETS WITH DIFFERENT DIAMETERS

The scour hole due to the plunging jets can be characterized by significant geometric dimensions which can undermine dam foundations. Therefore, a correct assessment of the main parameters influencing the erosive process is fundamental. In general, the equilibrium scour morphology mainly depends on the following parameters: jet impact angle into the stilling basin; jet densimetric Froude number; granulometric characteristics of the stilling basin material and tailwater level. In particular, the effect of these parameters can be different if scour hole morphology is either 2D or 3D. Furthermore, successive studies analyzed the erosive process due to multiple jets. The analysis of the scour process was conducted in the presence of both vertical and symmetric crossing jets. It has been experimentally proven that these two geometric configurations, in most of hydraulic conditions, determine a reduction of the scour hole lengths. Nevertheless, the scour process due to crossing jets is a complex phenomenon, as it depends on many parameters, including the crossing angles and the distance of the jet crossing point from the stilling basin water surface. To the authors’ knowledge, no studies are present in literature dealing with vertical crossing jets of different diameters. Therefore, a dedicated experimental apparatus is built in order to simulate two vertical crossing jets with different diameters. Experimental tests are conducted for different tailwater levels with different jet diameter ratios. The resulting morphology is compared with that due to a single plunging jet. This last configuration is obtained simply removing the pipe with smaller diameter from the experimental apparatus. The comparison is conducted in order to understand for which geometric configurations the presence of the smaller diameter jet becomes negligible in terms of scour hole characteristics