Large eddy simulation method for flood flow with large movement of free surface and wetting front

Akihiko Nakayama

Thursday 2 july 2015

16:45 - 17:00h at Oceania (level 0)

Themes: (T) Water engineering, (ST) Computational methods

Parallel session: 13E. Engineering - Computational

Hydrodynamic processes in natural rivers are very complex, especially along mid reaches of medium size rivers with varying slopes, sudden drops, acute bends, contractions, point bars and islands and plants and vegetation. Flow characteristics due to combinations of these factors often needed to find a better way of maintaining the flow rate and the environment. Numerical simulation methods that can cope with these complex situations are emerging rapidly especially those based on the three-dimensional Large-Eddy Simulation methods. We present a LES method that can reflect effects of rapidly changing free-surface flow in complex and natural geometry, especially, we show the method works in situations where the flow advances over dry beds or recedes from bars with large rocks totally or partially submerged. The method is based on a finite difference method using fixed rectangular grid with freely moving water surface treated by an original method similar to a VOF method. Special care is taken to correctly represent the boundary conditions on the bed, objects, the free surface and the advancing and retreating wetting front. We present basic validation in benchmark flows of curved channel and dam-break flows and then an example of analysis of flood flow of a real river in Japan. The extent of the inundation and the intensity of the bed shear at various stages of flood is reproduced very well.