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| RANS | LES |
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| The velocity field equations’ quantities are averaged with respect to time. | The equation of velocity field quantities is averaged with respect to space. |
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| The eddy structures are not solved, and therefore the model has to be calibrated with respect to the type of turbulent current under consideration, wherefrom their behaviour depends. | The eddy structures within the inertial range of the turbulent spectrum are solved by using a sufficiently fine grid, while the subgrid scales of motion are parameterized and modeled, as they can be considered isotropic. |
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| The motion can also be solved in two dimensions, if it is averagely static. | The motion can only be solved in three dimensions, because of the constant presence of the time derivatives due to the unstatic behaviour of the solved eddy structures. |
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| The equations’ number is cut within a predetermined order, and the unknown variables belonging to a higher order are modeled with approximate relations. | The equations’ number is cut with respect to the position within the inertial range, so the difference between what is computed and what is modeled is energetic rather than geometric. |
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| The closure problem is introduced by the Reynolds’s stresses’ tensor and is generally solved by using the turbulent cinematic viscosity, which often causes blunders. | The closure problem is introduced by the subgrid stresses’ tensor and is solved by subgrid models, which have no significant influence on the solution’s precision. |
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| High efficiency, especially for the k-e based closure. | Extra efficiency and computational precision. |
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| Low computational effort and CPU memory required. | High computational effort and CPU memory required. |
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