Author(s): Hideto Yoshimura, Kojiro Tani, Ichiro FUJITA
Linked Author(s): Hideto YOSHIMURA, Kojiro Tani, Ichiro FUJITA
Keywords: Free-surface turbulence; IBM; DNS; VOF; Rough-wall open channel;
Abstract: This paper reports the preliminary results from a direct numerical simulation of a shallow free-surface turbulent flow over a rough bed. The rough bed is composed of spherical roughness elements that are packed in a staggered arrangement. The roughness elements are represented by an immersed boundary method in an orthogonal coordinate system. The free surface is captured by a single-phase volume-of-fluid method that needs dynamic boundary conditions at the free surface. The results show some features of the free-surface patterns under different Froude number conditions. The wavenumber–frequency and directional frequency spectra show that the free-surface patterns are associated with both the dispersive and non-dispersive waves. The farmer waves follow closely the dispersion relation of gravity waves in an irrotational flow. In addition, the stationary waves also occurr at subcritical flow with ???≈0.5. The non-dispersive waves are induced by the interaction between the free-surface and the underlying turbulence, and therefore are advected with the surface velocity. The free-surface patterns obtained by the simulations have a similar feature to that observed in experimental studies by other researchers.