Large Eddy Simulation of Single-Phase Flow

For large eddy simulation of particle-laden turbulent flows, the accuracy with which the continuous phase is predicted is crucial for the simulation of the dispersed phase. In this chapter, issues that are important for LES of single-phase turbulent flow, including filtering, SGS modeling and numerics, are reviewed. Also, the advantage that LES holds over DNS and RANS to simulate practical single-phase turbulent flows is discussed.

The LES philosophy is based on the trivial observation that the loss of information incurred during filtering places a limit on the achievable accuracy of LES. Keeping that in mind, a broad array of SGS models for LES purposes have been developed using a variety of different approximations. Such models have been successful in many flows, yet they all have shortcomings.

There are many important issues in LES which make the validation of the results, and of the SGS models themselves, essential. The most obvious ones are those related to the physical modeling of the subgrid stresses, which is in many cases based on engineering approximations, justified by little more than dimensional considerations. Numerical issues are also important, since most models use as input the velocity gradients of the filtered field, which depend on the smallest scales resolved by the simulations, and therefore strongly influenced by numerical errors. Consistency with filtering of the physical models and numerical schemes adopted is as important as the previous issues.

Keywords: Large eddy simulation, turbulent flows, single-phase flow, filtering, sub-grid scales, eddy-viscosity models, scale-similar models, momentum conservation, consistency, numerical errors