The capability of a twin rotating controllers to suppress the harmonic force fluctuation on a square cylinder with 45◦ angle of incidence has been numerically investigated in the present study for a frequently studied laminar flow. A point by point searching strategy has been used to find the possible installing locations of the controllers performing complete suppression of the force fluctuation. All cases that suppressed the hydrodynamic force completely and/or semi-completely have been selected for further investigations. Obtained results show that only one installing location of the controllers is able to suppress the fluctuations of the hydrodynamic forces on the whole system completely. Of course, there is still a weak secondary harmonic vortex shedding downstream the whole of the system, which does not affect the made steady flow in the upstream and near-wake regions. Besides, the drag coefficients on the square cylinder and rotating controller decrease by 30.62% and 45.76%, respectively. Further investigation shows that the hydrodynamic forces on the square cylinder always fluctuate harmonically regardless of the controller location, and the harmonic frequency of the lift coefficient of the cylinder is the main frequency of the other periodic fluctuations in the flow field.
