An important phase of wind farm design is solving the wind farm layout optimization problem, which consists in optimally positioning the turbines within the wind farm so that the wake effects are minimized and therefore the expected power production maximized. Simulating a wind farm with more than one fully detailed wind turbine and possibly complex terrain geometry requires significant computational power and time. This paper concerns the study of the depth-averaged flow of the wind turbine with a CFD-RANS approach. The complex three-dimensional (3D) geometry need not be modelled or discretized in the pre-processing state: instead, the geometry of the terrain is only described with source terms in the depth-averaged equations, which are then solved in a very simple and fixed two-dimensional (2D) domain. This approach reduces the equations from 3D to 2D and decreases the elapsed time of CFD simulations from hours to minutes. Thus, it is a very practicable modelling method in real time optimization work. 2D CFD simulations are compared with full 3D models and experiments. This paper gives an overview of the existing work and discusses the challenges that may be overcome by future research.