Location

Virtual

Start Date

7-5-2021 12:00 AM

End Date

7-8-2021 12:00 AM

Description

Water jets impacting on a non-cohesive granular bed cause a dynamic pressure distribution on the surface of the scour hole. Such distribution greatly differs from the hydrostatic one, especially in proximity of the impact zone, where the kinetic energy of the jet is dissipates due to the shear stresses acting on the scour surface. Here, the excess of shear stress causes the erosion of the bed material and can lead to the failure of hydraulic structures. Therefore, a detailed analysis of the forces acting on the scour surface is fundamental to understand the erosion mechanisms. Experimental tests were conducted under 3D and 2D conditions. Under 3D condition, the channel was wide enough to allow the full lateral development of the scour hole, whereas it was narrowed by means of vertical plates to achieve the 2D condition. Tests were conducted by monitoring the pressure distributions along the axial profile of the scour hole under both static and dynamic equilibrium conditions. The most influential parameters governing the scour process have been identified and varied, including the water discharge, the jet angle and the tailwater depth. Finally, the pressure distributions pertaining to 2D and 3D cases were compared, suggesting the dependence of the relative pressure on the tailwater and on the densimetric Froude number, and two empirical equations predicting the maximum relative pressure in case of low and high values of tailwater have been derived for design purposes. The proposed analysis represents a contribution to the development of theoretical methods for jet-driven scour processes.

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Jul 5th, 12:00 AM Jul 8th, 12:00 AM

Comparison of Pressure Distribution in 2D and 3D Jet-Driven Scour Processes

Virtual

Water jets impacting on a non-cohesive granular bed cause a dynamic pressure distribution on the surface of the scour hole. Such distribution greatly differs from the hydrostatic one, especially in proximity of the impact zone, where the kinetic energy of the jet is dissipates due to the shear stresses acting on the scour surface. Here, the excess of shear stress causes the erosion of the bed material and can lead to the failure of hydraulic structures. Therefore, a detailed analysis of the forces acting on the scour surface is fundamental to understand the erosion mechanisms. Experimental tests were conducted under 3D and 2D conditions. Under 3D condition, the channel was wide enough to allow the full lateral development of the scour hole, whereas it was narrowed by means of vertical plates to achieve the 2D condition. Tests were conducted by monitoring the pressure distributions along the axial profile of the scour hole under both static and dynamic equilibrium conditions. The most influential parameters governing the scour process have been identified and varied, including the water discharge, the jet angle and the tailwater depth. Finally, the pressure distributions pertaining to 2D and 3D cases were compared, suggesting the dependence of the relative pressure on the tailwater and on the densimetric Froude number, and two empirical equations predicting the maximum relative pressure in case of low and high values of tailwater have been derived for design purposes. The proposed analysis represents a contribution to the development of theoretical methods for jet-driven scour processes.

 

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