Numerical Simulation on Retreating Blade Sections of a Small UAV Helicopter in Forward Flight

Abstract This study presents computational simulations for three different spanwise locations of the retreating blade of a small UAV helicopter rotor in forward flight. The aim of the present study is to focus on its aerodynamic performance within the reversed flow regime. The results provide an aerodynamic analysis for various angles of attack at three distinct spanwise sections, examining the impact of the Reynolds number on reversed flow characteristics. The analysis emphasizes key aerodynamic parameters, including lift and drag coefficients, within the reversed flow region, comparing the effects of different angles of attack. In addition, detailed boundary layer assessments are performed through the analysis of surface pressure and skin friction coefficients. The study reveals that as the advance ratio increases, the reverse flow spreads towards the tip of the rotor’s retreating blade. This results in a noticeable loss of lift, an increase in drag, and high unsteadiness, leading to unstable rotor operation. This effect is more pronounced at smaller angles of attack. However, at moderate angles, the loss of lift and the increase in drag at the tip become negligible compared to the inboard blade sections.