We have developed a new wind turbine system (WLT, WindLens Turbine) that consists of a diffuser shroud with a brim at the exit periphery and a wind turbine inside it. WLT has a bigger power output compared with a general same size wind turbine. This is because a low-pressure region due to a strong vortex formation draws more mass flow to the wind turbine inside the diffuser shroud. To investigate the three dimensional flow pattern around the WLT, numerical simulations are conducted with STAR-CCM+ using the LES for turbulent modeling and the moving boundary technique for rotating blades. In the simulation, it is confirmed that vortex rings are shed behind the brim alternately. However, we found an interaction with counter vortices formed between the tip vortex and the inside of the WindLens. In this report, behaviors of these vortices are investigated in more detail.