Overview of Turbulent Inflow Boundary Conditions for Large-Eddy Simulations

Generating realistic turbulent inflow conditions for large-eddy simulations and other large-scale-resolving approaches is essential to fully exploit the ever-increasing capabilities of modern computers in solving fluid flow problems of engineering interest. This research area has received much attention during the last two decades and will continue to grow as large-eddy simulation is applied to an even wider range of flows. It is deceptively difficult to generate turbulent inflow fluctuations that are realistic for a specific problem, and various methods have been designed to improve this realism. A review of such turbulent inflow boundary conditions is presented, broadly classified into transition-inducing approaches, turbulence library-based methods, recycling-rescaling-based methods, and synthetic turbulence generators. The last category is given more attention to cover a variety of creative approaches that are found in the literature as well as due to its practicality for problems of industrial interest. Selection of a particular method for a particular application is a compromise between the required fidelity and the allowable complexity and computational expense. Lack of quantitative knowledge about turbulence to be fed into the simulation is recognized as a limiting factor in the effective use of such inflow generators for problems of practical interest.