Hydraulics & Waterways

Oral

397821 - Developed and developing phases in the scour process induced by jets: New experimental evidence and theory

Tuesday, June 5
4:00 PM - 5:30 PM
Location: Regency Room
Co-Authors: Michele Palermo, Pisa, Italy – University of Pisa; Stefano Pagliara, Pisa, Italy – University of Pisa

The scour of granular materials due to jets is a very complex problem because of its intrinsic three-dimensional (3D) nature. It is still an unsolved problem of fluid mechanics. Recent experimental evidence concerning the scour evolution for sub-vertical plunging jets highlights the presence of two clear stages in the scour process: 1) the developing phase, occurring at the very first instants of the process, when the jet entering the water body impacts the granular bed material and starts removing sediment to further continue forming the downstream dune; 2) the developed phase, when the scour hole and dune evolution is characterized by a proportional (homothetic) expansion of the main geometric lengths and the scour origin does not shift significantly. During the developing phase, the flow structure is essentially 3D and the role of the momentum horizontal component is significant. During the developed phase, the flow structure within the scour hole can be either quasi-cylindrical (2D) or fully 3D, according to the resulting scour pothole shape and channel geometry. In this paper, we expand those previous experimental studies for a large range of jet angles, including vertical plunging jets. New experimental tests show that the jet inclination plays a prominent role on the nature of the transition between the two phases; they furnish further insights on the quantitative assessment of the non-dimensional time variable in which the transition occurs. The paper is supplemented with a theory which elegantly predicts the time evolution of the scour process.

Fabian Alejandro Bombardelli, PhD

Professor
Univ. California at Davis

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