This master thesis discusses CFD simulations of the flow with a thick boundary layerover a cube obstacle. This type of flow can be a good representation of more complexphenomena, such as flow over a train roof with box-shaped equipment or wind attackinga building. Therefore, this work is intended to serve as a baseline for further discussionon similar flow cases with more complex geometry.In this project, six different flow cases were simulated. The discussed cases differed fromeach other in three ways: used computational mesh, used turbulence model, and appliedinlet boundary condition. Before launching CFD simulations, two different computationalmeshes were created. They were constructed with divisions into smaller sub-domainsto allow greater control over mesh characteristics in essential regions such as the wakebehind the cube. Three simulations were performed using (RANS) turbulence models,whereas three other simulations were performed with a hybrid RANS-LES turbulencemodel. Finally, predefined velocity and turbulent stress profiles were imposed at theinlet boundary to create a thick boundary layer upstream of the cube. Additionally,synthetic turbulence fluctuations were added to the inflow boundary condition for onehybrid turbulence model case.The result of this work showed that already, with the coarser computational mesh, RANSsimulations were able to provide satisfactory results that resemble well actual physicalphenomena. As for the simulations with the hybrid turbulence model, it turned outthat the location of the transition between RANS and LES resolver depends much onthe mesh resolution. With the finer mesh resolution around the cube, the hybrid modelstarts to resolve turbulence around the cube with LES mode. Moreover, the addition ofsynthetic turbulence to the inflow boundary condition results in LES dominance in thewhole resolved flow field.