Results of direct numerical simulations for time-developing air naturalconvection boundary layer are presented. Computations have been performed assuming periodicity conditions in both the directions parallel to the vertical isothermal hot plate. The contribution is mainly focused on understanding of laminar-turbulent transition peculiarities in the case of perturbation action of external turbulence that is modeled by isotropic disturbances initially introduced into the computational domain. Special attention is paid to identification and analysis of evolving three-dimensional vortices that clearly manifest themselves through the whole stages of laminar-turbulent transition in the boundary layer. A comparison of computed profiles of mean velocity, mean temperature and fluctuation characteristics for turbulent regimes of convection with experimental data is performed as well.
Dam-break turbulent flow interacting with obstacles is simulated with the VOF method implemented in an in-house unstructured-grid finite-volume Navier-Stokes code. A special attention is paid to prediction of separation phenomena using low-Re computational grids that provide full resolution of viscous sublayers on the bottom and side confining walls, if any. Some original developments aimed at improvement of the VOF method robustness for such kind of flows are presented. The test case considered is interaction of the dam-break induced water stream with a triangular obstacle. Computations under conditions of experiments by Soares-Frazao (2007) have been carried out on the base of 2D and 3D formulations. It is shown that action of the bottom wall friction leads to formation of one or two separation "bubbles", depending on the flow development phase, and to occurrence of associated hills at the free surface, which are observed in experimental photos as well. Taking into account presence of side walls of the experimental channel results in solutions with a considerably 3D shape of the computed free surface, and its side view much better agrees with the experimental photos than that given by 2D solutions. Moreover, local-in-time separation of the flow from the side walls is predicted with the 3D formulation.
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