Leading Edge Vortex Generators installed on a wind tunnel model
In the department of helicopters, a range of active and passive flow control mechanisms are being investigated using experiments and numerical methods. In order to reduce the drag on the advancing blade, camber control devices are being investigated, including Miniature Trailing Edge Devices (Mini-TEDs) and trailing edge flaps. To reduce the effects of flow separation on the retreating blade, the DLR/ONERA project SIMCOS is investigating separation control with air jets and with “Leading Edge Vortex Generators” (LEVoGs). Both of these methods reduce the pitching moment peak caused by the onset of Dynamic Stall, and are investigated using both numerical simulations with the DLR-TAU code and wind tunnel experiments.
Flow control with air jets is an active method of improving the flow using constant blowing or air pulses with a frequency of up to 500Hz from holes or slots in the top of the airfoil. As an active control measure, these jets can simply be turned off when no flow control is necessary. LEVoGs are a passive flow control method where rubber discs are glued to the leading edge of the rotor blade, causing a measurable improvement in the dynamic flow behaviour at high angles of attack. In addition to the standard measurement techniques for unsteady flow (pressure and force measurements), a range of new optical methods are used, including tomographic Particle Image Velocimetry (PIV) to map the flow field and optimise the flow control devices.