Numerical modeling of turbulence in lares and reservoirs with Large Eddy Simulation technique

The paper shows the application of a finite element model to simulate the flow and turbulence characteristics of very complex natural geometry. The flow phenomena in natural geometry such as lakes and reservoirs are very complex and in most cases fully three-dimensional. This is due to the irregular boundaries, the large volume of the water body and the variability of the external forces on the water body. Numerical models must at least be able to simulate the large scale processes in correspondence of the influence of wind forces, momentum induced by in- and outflow and the coriolis force. Another problem is the large spectrum of turbulence existing in large natural geometry. Standard statistic models based on the Reynolds-equations are widely used, but it is very difficult to model the whole spectrum correctly which depends on the individual reservoir. Additionally strong anisotropic flow characteristics demand an anisotropic turbulence model. Direct Numerical Simulation would require more computer capacities than available thus a very promising approach is the Large-Eddy-Simulation technique. This paper presents the numerical method which is based on a Finite Element model in conjunction with a mixed model LES technique. The results of the validation study on flow phenomena in an idealized lake are discussed as well as the turbulence characteristics in large irregular water bodies.