Numerical simulation of a rotating blade using a flat-plate airfoil at low Reynolds numbers for Mars helicopter

To realize a high-performance rotor for a Mars helicopter, the aerodynamic performances and flow characteristics around a rotating blade using a flat-plate airfoil at low Reynolds numbers have been investigated. Numerical simulations have been conducted using a CFD solver of rFlow3D, which has been developed in JAXA for a rotorcraft simulation. The ambient pressures are set to 100 kPa, 50 kPa, 10 kPa, and 5 kPa, corresponding to the Reynolds numbers of 77000, 39000, 7700, and 3900 based on the blade tip velocity and the tip chord length respectively. The thrust and torque coefficients agree well with the previous experimental study for the cases with pitch angles up to 10 deg. The influences of the ambient pressure on the aerodynamic characteristics are not so significant in the cases with low pitch angles. On the other hand, the flow characteristics become highly different between the cases with the ambient pressure of 100 kPa and 5 kPa. For the 5 kPa case, the secondary vortex inside the leading-edge vortex is clearly recognized. In addition, the interaction of the tip vortices with the leading-edge vortices becomes significant, resulting in the reduction of the negative pressure region near the wing tip.