Contradictions in the Large-Wavelength Approximation of Turbulent Flow Past a Wavy Bottom
What’s just barely more complicated than a parallel channel flow? A lightly (and slowly) perturbed parallel channel flow. Yet the properties of turbulence, as extracted from a direct numerical simulation, can be very different. One practical example arises in a widespread geophysical application: the formation of ripples in sand. Common wisdom is to use an eddy-viscosity turbulence model to describe it. Our own work on this problem, started in the same vein years ago, was contradicted by simulations using a volume force to represent the streaming effect of the bottom shape modulation. Now, new simulations using an immersed boundary to represent the actual shape of the wall unfold the contradiction: the scales of length involved are much larger than anticipated.
KeywordsDirect Numerical Simulation Eddy Viscosity Wavy Wall Bottom Shear Stress Sand Ripple
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