Abstract
This study evaluates the capability of Navier–Stokes solvers in predicting forward and backward plunging breaking, including assessment of the effect of grid resolution, turbulence model, and VoF, CLSVoF interface models on predictions. For this purpose, 2D simulations are performed for four test cases: dam break, solitary wave run up on a slope, flow over a submerged bump, and solitary wave over a submerged rectangular obstacle. Plunging wave breaking involves high wave crest, plunger formation, and splash up, followed by second plunger, and chaotic water motions. Coarser grids reasonably predict the wave breaking features, but finer grids are required for accurate prediction of the splash up events. However, instabilities are triggered at the air–water interface (primarily for the air flow) on very fine grids, which induces surface peel-off or kinks and roll-up of the plunger tips. Reynolds averaged Navier–Stokes (RANS) turbulence models result in high eddy-viscosity in the air–water region which decays the fluid momentum and adversely affects the predictions. Both VoF and CLSVoF methods predict the large-scale plunging breaking characteristics well; however, they vary in the prediction of the finer details. The CLSVoF solver predicts the splash-up event and secondary plunger better than the VoF solver; however, the latter predicts the plunger shape better than the former for the solitary wave run-up on a slope case.
Highlights
OpenFOAM simulations have been performed for four test cases: the dam break case; the run-up of solitary waves with different wave heights over a slope resulting in either no-breaking, surging, or forward plunging breaking; the uniform flow over a submerged bump—resulting in backward plunging breaking due to blockage of the downstream flow because of hydraulic jump; and the solitary wave flow over a submerged obstacle—which results in backward plunging breaking due to flow circulation induced by vortices shed from the obstacle
The study evaluates the capability of Navier–Stokes solvers in predicting forward and backward plunging breaking caused by either flow acceleration or flow reflection from the wall or submerged obstacle induced vortices, including assessment of the effect of grid resolution and turbulence modeling on the predictions and comparison of VoF and coupled level-set and VoF (CLSVoF) air–water interface modeling methods
Four test cases were considered: dam break—which involves backward plunging breaking due to flow reflection from the wall; run-up of solitary waves over a slope—resulting in either no-breaking or surging or forward plunging breaking; uniform flow over a submerged bump—resulting in backward plunging breaking due to blockage of the downstream flow because of hydraulic jump; and solitary wave flow over a submerged obstacle—resulting in backward plunging breaking due to flow circulation induced by vortices shed from the obstacle
Summary
Studies have investigated the effect of submerged and emerging obstacles (or breakwaters) on the breaking wave pattern, as elaborated below. Grilli et al [6] investigated both experimentally and computationally (using potential theory) solitary wave breaking induced by the presence of submerged and emerged trapezoid breakwaters. It was reported that the height of the submerged breakwater (h), the solitary wave amplitude H0 and the water depth h0 influence both the type and the direction of the wave breaking. Studies [10,11,12] performed experiments and numerical simulations using a Navier–Stokes model to investigate the wave breaking for uniform flow over a submerged bump. Colagrossi and Landrini [15] performed numerical simulations for this case using smooth particle hydrodynamics For this test case the collapsing water column reflected from the wall resulting in backward plunging breaking wave
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