A primary distributed suction located at the close upstream of center-belt in HAWT (Hyundai Aero-acoustic Wind Tunnel) has been a major source of static pressure gradient inside a plenum. This gradient, however, is further augmented by a vortex generating (VG) system, which has been installed recently to mitigate aerodynamic data fluctuations. To alleviate the steep static pressure gradient, an optimal configuration of a boundary layer control system is investigated numerically regarding the static pressure gradient as well as the corresponding boundary layer thickness inside the plenum. Various configurations are investigated for the primary suction and scoop, secondary tangential blowing slot. With the combination of the primary suction (or scoop) and tangential blowing slot, a flatter static pressure gradient is obtained without sacrificing a boundary layer thickness compared to the current configuration. Secondly, a new VG configuration with less deviation in static pressure gradient is suggested by numerical investigations. In terms of reducing the aerodynamic data fluctuation, this new VG is experimentally proven to show comparable performance to the original VG.