Numerical study of the effect of trailing edge flap on helicopter brownout based on the CFD-DEM coupling method

Brownout is a phenomenon encountered by helicopters in sandy and dusty environments, where sand clouds create a degraded visual environment, frequently leading to flight incidents. This paper explores the feasibility of using helicopter trailing edge flaps to alleviate brownout and examines the impact of flap deflection on brownout characteristics during hovering. Focusing on the C-T rotor and Robin fuselage, the study places one trailing edge flap on each blade. The SST k-ω turbulence model and overset mesh technique are utilized to calculate the rotor flow field, while sand particle motion is simulated using the DEM method based on the Hertz-Mindlin contact model. The motion process of sand particles under rotor flow is computed via the CFD-DEM one-way coupling method. The tip vortex position of the Lynx rotor and the pressure coefficient of the C-T rotor are validated against experimental data. Rotor flow field characteristics and sand cloud characteristics are analyzed for the C-T rotor blade with 10°upward flap deflection, 10°downward flap deflection, and no flap deflection. Results show that upward flap deflection reduces the average height of suspended sand particles, while downward deflection increases it. The results indicate that trailing edge flaps have potential as an effective means to mitigate brownout in helicopter operations.