Sub-grid scale (SGS) models are required in order to model the influence of the unresolved small scales on the resolved scales in large-eddy simulations (LES),udthe flow at the smallest scales of turbulence.udIn the following work two SGS models are presented and deeply analyzed in terms of accuracy through several LESs with different spatial resolutions, i.e. grid spacings.udThe first part of this thesis focuses on the basic theory of turbulence, the governing equations of fluid dynamics and their adaptation to LES. Furthermore, two important SGS models udare presented: udone is the Dynamic eddy-viscosity model (DEVM), developed by cite{germano1991dynamic}, while the other is the Explicit Algebraic SGS model (EASSM), by cite{marstorp2009explicit}.udIn addition, some details about the implementation of the EASSM in a Pseudo-Spectral Navier-Stokes code cite{chevalier2007simson} are presented.udThe performance of the two aforementioned models will be investigated in the following chapters, by means of LES of a channel flow, with friction Reynolds numbersud$Re_au=590$ up to $Re_au=5200$, with relatively coarse resolutions. udData from each simulation will be compared to baseline DNS data.udResults have shown that, in contrast to the DEVM, the EASSM has promising potentials for flow predictions at high friction Reynolds numbers: the higher the friction Reynolds numberudis the better the EASSM will behave and the worse the performances of the DEVM will be.udThe better performance of the EASSM is contributed to the ability to capture flow anisotropy at the small scales through a correct formulation for the SGS stresses.udMoreover, a considerable reduction in the required computational resources can be achieved using the EASSM compared to DEVM. Therefore, the EASSM combines accuracy and computationaludefficiency, implying that it has a clear potential for industrial CFD usage.
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