Aerodynamic Flow Control using a Variable Droop Leading Edge Airfoil
NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF MECHANICAL AND ASTRONAUTICAL ENGINEERING
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Control of dynamic stall under compressible flow conditions appropriate for a helicopter rotor has been demonstrated using a variable droop leading edge airfoil. The airfoil leading is drooped in phase with its sinusoidal pitch oscillations to eliminate the dynamic stall vortex that induces many adverse effects on the blade. The approach results in dramatic reductions in drag and pitching moment, while also decreasing the maximum lift slightly. This loss was recovered using a trailing edge mounted vertical Gurney flap of 1 chord height, without undue drag penalty. Drooping the leading edge substantially modifies the airfoil pressure distribution such that the dynamic stall onset mechanism is changed from shock-induced to pressure gradient induced for certain flow conditions. The changes also manifest in significantly lowered peak vorticity fluxes preventing the flow vorticity from coalescing into a very tightly organized dynamic stall vortex. The behavior of transition and its role in the process are also addressed.
- Fluid Mechanics