The potential application of flow control to helicopter rotor blades

A range of flow control devices are reviewed for their suitability to suppress or eliminate various aerodynamic flow phenomena. Specifically, those devices which may lend themselves to control the flow on helicopter rotor blades are identified. Four types of flow control device are identified as possible candidates, namely (i) air-jet vortex generators, (ii) sub-boundary layer vortex generators, (iii) surface blowing circulation control and (iv) movable flaps. As an extension to this work, Computational Fluid Dynamics (CFD) calculations are performed on a static RAE9645 aerofoil at 18° incidence incorporating corotating air-jet vortex generators at 12% chord . The results are compared to relevant experimental data. It was found that the Spalart-AIImaras turbulence model showed promise in being able to recreate the beneficial effects of air-jet vortex generators to delay flow separation at high incidence. With this model the normal lift coefficient was increased from 1.22 to 1.65, corresponding well with experiment. In addition, a rotor performance code was used to predict the operational advantages of employing air-jet vortex generators on helicopter rotor blades. This study indicated increases in forward speed of around 20kts were possible, but the possibility of increasing the all-up mass indicated less benefit.

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