Computational Study on the Aerodynamic Interference Between Tandem Rotors and Nearby Obstacles

Abstract

The tandem rotor/ground-obstacle interference problems that occur during landing operations produce high pilot workloads. In this study, a vortex-based aerodynamic solver is employed to investigate the flowfields and air loads of a tandem rotor near ground obstacles. The unsteady air loads of the multirotors are simulated using a panel method, and the wake of the tandem rotor is modeled by a vortex particle method. A viscous boundary model accounts for the effects of surrounding obstacles. The method is applied to a th-scaled model of a CH-47D operating near the ground, and the results are compared with those from experiments. The rotor-induced inflow predicted by the numerical model compares reasonably well with the experimental data. Contrary to a tandem rotor operating without obstacles, the rotor wake is deflected by the ground and the obstacle, generating recirculation. As opposed to single forward and aft rotors, the aerodynamic interactions of tandem rotors reduce the lift in the rotor-overlapped region, changing the strength of the recirculation near the ground and obstacles. The starboard side experiences stronger recirculation and a greater decrease in tandem rotor thrust because the rotational directions of the tandem rotor yield a stronger outwash on the starboard side.