Robustness and limits of vortex generator effectiveness in helicopter drag reduction

The effect of vortex generators on helicopter drag was investigated in a wind tunnel test. An array of counterrotating vortex generators was mounted on the rear ramp of a heavy-class helicopter model, slightly downstream of the fuselage upsweep. The wind tunnel campaign also included tests with a radome positioned upstream of the vortex generators to evaluate the robustness of the vortex generators. At cruise angle of attack, a drag reduction of about 2% with respect to the complete helicopter configuration was measured for the baseline fuselage configuration with the vortex generator array installed. The range of angles of attack and sideslip where the vortex generators were effective for drag reduction was established. The addition of a radome mounted upstream on the fuselage lower side renders the vortex generators ineffective. However, for the model attitudes where the vortex generators were ineffective, the vortex generators did not increase helicopter drag. Steady and unsteady pressures measured on the fuselage rear ramp revealed the flow behavior due to the presence of the vortex generators.