Numerical Investigations of Bump Effects on the Performance of Double-Ended Airfoils and ABC Rotors

Numerical simulations based on RANS have been performed to investigate the aerodynamic characteristics of the double-ended airfoil deformed by local bumps on its lower surface, both in airfoil and coaxial rotor environments. The two-dimensional results show that the bump can reduce the magnitude of negative lift but increase the drag at large negative AoAs and high Mach numbers, and can increase the stability of the airfoil at positive AoAs in forward flow and at large negative AoAs in reverse flow. A bump has a more significant effect on airfoil performance if it is closer to the leading edge and has a larger area. A coaxial rotor with different double-ended airfoils deformed by bumps located inboard was predicted under a 0.5 advance ratio with a lift-offset of 0.3. Bumps under such flight conditions influence the root region on the advancing side more than on the retreating side. The root region at 14 ~ 33% span produces about 6% of the total thrust, so bump’s effects on the whole performance are insignificant. Through the flow details around inboard sections, it suggests that bumps have the potential to improve ABC rotor performance, and flight conditions and blade geometry should be considered in conjunction with the application of bumps for effectiveness. Although the double-ended airfoil only covers the blade range of 0.14 ~ 0.33R, the total rotor thrust is slightly increased by adding bumps, and a higher bump has a greater influence.