An experimental and numerical investigation was performed to analyze the flow structures and momentum transfer in the wake of a turbine with blockage ratios of 18%, 26%, and 35%. In the experimental setup, an acoustic Doppler velocimeter was used to measure wake velocity. Numerical modeling was executed with Wall-Modeled Large-Eddy Simulation and validated with the experimental data. In general, a satisfactory correlation between numerical and measured velocity deficit was obtained. In the near wake, numerical results overpredicted the measurements at the rotor center level, but agreement was better for the outer radii. The blade tip vortices were coherent within the near wake and characterized by stable helical trajectories, synchronized with the blade rotation frequency. Furthermore, the high blockage values prevented the vortices from expanding beyond the blade tip level and increased the source of momentum around the rotor. Then, the higher the proximity of lateral boundaries, the faster the wake recovered, allowing shorter separation distances to be suggested between multiple devices in a tandem arrangement.