Within the scope of this thesis, a new method to generate an initial turbulent velocity field for a numerical simulation within the CFD software-package MGLET is investigated. The aim is to generate a fully developed flow for a wall bounded geometry. This thesis examines whether the method currently used in MGLET can be improved in terms of stability, usability and efficiency. A literature review shows that various approaches to solve this task exist, these are categorized into transition-inducing approaches, synthetic inflow generation methods and precursor simulation methods. In this thesis, four different methods for the generation of an initial turbulent velocity field are tested, compared and evaluated under consideration of the temporal development of the averaged flow quantities, based on the property that fully developed flows are statistically stable. To investigate the methods, the geometry of an open duct is used as a model. In the first and currently used method, random white-noise is superimposed on a uniform velocity. This method requires a high initial Reynolds number which can be increased after realistic fluctuations developed, by adjusting the viscosity. The second method takes into account the log-law boundary layer for the walls. As third method, proposed by J. Mann, is applied which constructs spatially correlated fluctuations for an atmospheric boundary layer wind field by applying an inverse fast Fourier technique. In this thesis, the open-source code TuGen is used to generate the fluctuations by Mann. This thesis examines the procedure for using the Mann’s method for a wall-bounded flow. For this purpose, a detailed sensitivity analysis of the three input parameters alpha epsilon 2/3 , L, Gamma is performed. This shows that the input parameters are not very sensitive which allows the application to wall bounded geometries. The fluctuations are very stable and can trigger turbulence for an initial friction Reynolds number Reτ = 180. The new method does not depend on an accurate description of the target turbulence. In fourth method, Mann’s fluctuations are superimposed on a log-law boundary layer, which reduces the adaption region to develop realistic fluctuations. The last method is recommended as a new application for initializing a turbulent velocity field in MGLET.     «

Within the scope of this thesis, a new method to generate an initial turbulent velocity field for a numerical simulation within the CFD software-package MGLET is investigated. The aim is to generate a fully developed flow for a wall bounded geometry. This thesis examines whether the method currently used in MGLET can be improved in terms of stability, usability and efficiency. A literature review shows that various approaches to solve this task exist, these are categorized into transition-induci...     »