Airfoil optimization for Mars rotorcraft blade at large angle of attack and experimental verification

Although the thin and cold Martian atmosphere provides the feasibility of rotorcraft flight on Mars, rotors designed for denser Earth atmosphere with small angles of attack hardly generate enough thrust for rotorcraft flight at conventional rotational speeds in the Martian atmosphere. In this paper, we employ the Particle Swarm Optimization (PSO) algorithm to search for the control points of the Bezier curve, completing the parameterization of the airfoil upper and lower curves based on these control points. In order to directly enhance the lift-to-drag ratio of the airfoil at high angles of attack, the NSGA-II algorithm is utilized to optimize the lift-to-drag ratio of NACA 6904 at α = 17.5°, Ma = 0.43, Re = 7 600, and CLF 5605 at α = 15°, Ma = 0.7, Re = 7 481, respectively. The two-dimensional RANS (Reynolds Average Navier-Stokes) and k-ω SST turbulence models are employed in the optimization process by CFD to predict the lift and drag characteristics of the airfoil in a Martian environment. Under simulated Mars atmospheric conditions (pressure of 1 380 Pa, test temperature of 24 °C, equivalent Mars atmospheric density at the surface of 0.016 2 g/cm³), the airfoil after optimized is subjected to rotor lift-drag characteristic tests where a single-rotor lift-drag characteristic test bench is employed for verification. The experimental results demonstrate that the RB-TB-II blade, which is obtained by optimizing the airfoil based on the RB-SWQ-I blade, exhibits a 19.6% increase in Power Loading (PL) and a 20.4% increase in Figure of Merit (FM) compared with the RB-SWQ-I blade. Based on the results of airfoil optimization, increasing the camber at the leading edge of the airfoil under high angles of attack contributes to an improved lift-to-drag ratio.