The case of the flow around a rotating circular cylinder is very complex. This thesis investigates the properties of a fluid flow for Reynolds numbers ranging from 50 to 400. Numerical simulations are performed using a combination of isogeometric analysis and the residual-based variational multiscale method, providing high accuracy. The results show how the lift and the drag generated by the cylinder are related to the spin rate and the Reynolds number. When comparing the lift and drag values to the required amount of torque which is needed to spin the cylinder, it is shown that at medium spin rates, a very high aerodynamic efficiency is obtained at a reasonable amount of torque. 3D simulations are performed and show at high spin rates strong vorticity and a wake that is dominated by vortex shedding. These results differ strongly from the 2D simulations, which leads to the question whether 2D simulations are still representative for real real at high spin rates, despite the low Reynolds number.