Abstract
Breaking surge waves are highly turbulent three-dimensional (3D) flows, which occur when the water flow encounters a sudden change in depth or velocity. The 3D turbulent structures across a breaking surge are induced by the velocity gradient across the surge and phase discontinuity at the front. This paper examined the turbulent structures in breaking surge waves with Froude numbers of 1.71 and 2.13 by investigating the air entrainment and perturbation patterns across the surge front. A combination of the Volume Of Fluid (VOF) method and Large Eddy Simulation (LES) was utilized to capture air entrainment and turbulent structures simultaneously. The 3D nature of the vortical structures was simulated by implementing a spanwise periodic boundary. The water surface perturbation and air concentration profiles were extracted, and the averaged air concentration profiles obtained from the numerical simulations were consistent with laboratory observations reported in the literature. The linkage between turbulent kinetic energy distribution and air entrainment was also explored in this paper. Finally, using quadrant analysis and the Q-criterion, this paper examined the role of the spanwise perturbations in the development of turbulent structures in the surge front.
Highlights
A critical consideration for Large Eddy Simulation (LES) is the selection of the filter size that can resolve the majority of large-scale energy-containing eddies
A general and widely used method to estimate the quality of LES results was introduced by Pope [18], who suggested that the resolved Turbulent Kinetic Energy (TKE), denoted by kres, should be more than 80% of the total TKE to enable a well-resolved simulation
In the scope of this paper, we investigated the turbulent structures across breaking surge waves, highlighted the 3D behavior of velocity perturbations, and examined their linkage with the instability mechanisms in breaking surge waves
Summary
One of the main characteristics of propagating surge waves and hydraulic jumps is the discontinuity in water depth and velocity across the wave front. These waves have been historically known to be analogous to shock waves in compressible flow [3] as both categories are compression waves of finite amplitude. This analogy is founded on the basis of the similarity between shallow water equations and two-dimensional gas flow equations, as recently described by Karimpour and Chu [4,5]
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