Static scour features for steady and unsteady jet flows

Scour processes downstream of hydraulic structures are challenging problems in hydraulic engineering. Many studies were carried out in the past, and others have been recently conducted to assess the effects of hydraulic and geometric parameters on the scour phenomena caused by plunging jets. However, to the best of the authors' knowledge, there are no studies dealing with jet-driven scour processes under unsteady flow conditions. Therefore, the aim of this paper is to contribute to fill this gap of knowledge, presenting a preliminary analysis of the static equilibrium configuration (i.e., the equilibrium morphology when the jet action ceases). To this end, we conducted an experimental campaign varying jet discharge during each test. More specifically, for unsteady tests different hydrographs were simulated. In addition, reference tests were conducted under steady flow conditions. We found that static equilibrium configurations under unsteady flow conditions are significantly different from the reference counterpart (i.e., under steady conditions). Namely, both the water depth and the characteristics of the inflow hydrograph influence the static equilibrium morphology. In this regard, it is worth mentioning that under unsteady flow conditions and for low water depths, the scour hole is deeper than the reference tests. The opposite occurs for higher water depths. Overall, our preliminary analysis provides interesting insights on static scour features caused by plunging jets under both steady and unsteady conditions. Nevertheless, further analyses are required to assess the effect of jet characteristics on the dynamic equilibrium morphology.