Experimental Investigation of Passive and Active Flow Control for X2 Technology Hub and Fuselage Drag Reduction

The effects of passive, active, and combined flow control on the aerodynamic performance of an unpowered, bladeless 1/5th scale model of the X2 Technology™ Demonstrator have been assessed through a variety of surface and off-body measurements in a low-speed wind tunnel test, Re = 88x10³ [1/ft] and M∞ = 0.13. The baseline model employs a state-of-the-art low-drag coaxial hub design. Further drag reduction was investigated through minor design alterations, endplates, vortex generators, steady blowing and suction, and oscillatory blowing. Each drag mitigation control approach was individually assessed. Flow control technologies that produced the most promising test results were combined for further augmented performance. Six-component external balance loads, independent hub and tail loads, and surface and wake flow and pressure measurements were used to determine aerodynamic performance and the detailed physics of the flow control attributes. The wind tunnel test showed that the addition of endplates provided vehicle drag reduction of 4%. Steady blowing from the rotor shaft fairing reduced drag 4% and the combination of endplates and blowing decreased drag 6-8%.