Phys. Rev. Lett. 2014 (1/3)

Direct numerical simulations of capillary wave turbulence
L. Deike, D. Fuster, M. Berhanu, E. Falcon

This work presents Direct Numerical Simulations of capillary wave turbulence solving the full 3D Navier Stokes equations of a two-phase flow. When the interface is locally forced at large scales, a statistical stationary state appears after few forcing periods. Smaller wave scales are generated by nonlinear interactions, and the wave height spectrum is found to obey a power law in both wave number and frequency in good agreement with weak turbulence theory. By estimating the mean energy flux from the dissipated power, the Kolmogorov-Zakharov constant is evaluated and found to be compatible with the exact theoretical value. The time scale separation between linear, nonlinear interaction and dissipative times is also observed. These numerical results confirm the validity of weak turbulence approach to quantify out-of equilibrium wave statistics.

Chemical Engineering Science (2/3)

Multi-scale flow simulation of automotive catalytic converters
C. Ozhan, D. Fuster, P. Da Costa

The flow distribution within the automotive catalytic converter is an important controlling factor on the overall conversion efficiency. Capturing the flow features minimizing the computational cost is the first important step towards the solution of the complex full engineering problem. In this work we present a novel approach that combines physical and numerical multi-resolution techniques in order to correctly capture the flow features inside an automotive catalytic converter. While Adaptive Mesh Refinement techniques are optimized in order to minimize the computational effort in the divergent region, a novel subgrid model is developed to describe the flow inside the catalytic substrate placed between the convergent and divergent regions. The proposed Adaptive Mesh Refinement methods are tested for two test cases representative of the flow features found in the divergent region of a catalytic converter. The performance of the new subgrid model is validated against the non-uniformity index and the radial velocity profile data obtained by Benjamin et al (2002). The effective coupling of AMR techniques and the subgrid model significantly reduces the error of the numerical predictions to 5-15\% in conditions where the full simulation of the problem is out of current computational capabilities.

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