Browse Publications Technical Papers 2018-01-0185
2018-04-03

Influence of Discretization Schemes and LES Subgrid Models on Flow Field Predictions for a Motored Optical Engine 2018-01-0185

Large-eddy simulations (LES) of a motoring single-cylinder engine with transparent combustion chamber (TCC-II) are carried out using a commercially available computer code, CONVERGE. Numerical predictions are compared with high-speed particle image velocimetry (PIV) measurements. Predictions of two spatial discretization schemes namely, numerically stabilized central difference scheme (CDS) and fully upwind scheme are compared. Four different sub-grid scale (SGS) models; a non-eddy viscosity dynamic structure turbulence (DST) model of Pomraning and Rutland [AIAA Journal, 40, 2002], one-equation eddy-viscosity (1-Eqn) model of Menon et al. [Computers and Fluids, 1995], a zero-equation eddy-viscosity model of Vreman [Physics of Fluids, 2004] and the zero-equation standard Smagorinsky model [Smagorinsky, 1963] are employed on two different grid configurations. Additionally, simulations are also performed by deactivating the LES SGS models. It is found that the predictions when using the numerically stabilized CDS are significantly better than with the fully upwind scheme. The LES SGS models clearly make an impact on predicted flow field, although, the impact is not always positive. Overall, the eddy-viscosity model by Vreman provided the best predictions of flow statistics compared to the other LES models used in this work. A parameter called Convergence Index (CI), which is an indication of the magnitude of similarity or dissimilarity between two velocity fields, is introduced to assess the number of cycles required to calculate flow statistics. Interestingly, It is found that for the present study only ten cycles are sufficient to obtain statistically convergent mean and root mean squared (RMS) values of velocity fluctuations.

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