Experimental and theoretical analysis of jet induced scour depth under unsteady flow conditions

In this thesis we address the problem of scour hole caused by a jet plunging into a water pool, laying on a bottom of granular cohesionless material. This is a crucial problem, as scour phenomena occur in many engineering applications. Researchers have widely explored this topic by adopting empirical or semi-theoretical approaches. Although these studies furnished many practical equations to predict the scour geometry, such formulas are valid only in the tested range of parameters and they do not provide exhaustive insights on the physics of the process. This thesis follows the recent theoretical advancements pioneered by Bombardelli and collaborators, who derived completely theoretical formulas to predict the equilibrium scour depth of the pothole and its evolution under steady flow conditions, using dimensional arguments and the phenomenological theory of turbulence (PTT). We focused on the physics of the scour process under unsteady flow conditions and extended the theory proposed by Bombardelli et al. (2018). Our experimental data confirmed their findings, i.e., two phases occur during the scour evolution (developing and developed) regardless of the jet flow characteristics. The PTT-based model developed by Bombardelli et al. (2018) shows a good predicting capability of the scour evolution under unsteady flow conditions, thus confirming the validity of the scaling expression adopted for the shear stress. Our analysis provides further confirmations of the universal applicability of the PTT-based approach for jet-driven scour problems