Computational and experimental aeromechanics analysis of a coaxial rotor system in hover and forward flight

The aerodynamics and dynamics of a sub-scale coaxial rotor model designed for high-advance-ratio forward flight were investigated by means of a comprehensive analysis, hover and wind tunnel testing. Measurements were used to calibrate and validate the numerical predictions. The dynamics of the rotor system were analyzed with a focus on the interactional aerodynamics responsible for increased vibratory hub and blade loads. Reduced-order aerodynamics modeling using a free vortex wake method was used to ensure computational efficiency. Predictions of performance as well as blade flap bending deflections showed good correlation with the measurements. Transient axial hub loads also correlated well with the measurements by means of average loads, transient trends, and vibratory peak load characteristics. Furthermore, strong rotor-rotor interactions were seen, including blade-vortex interactions. At high advance ratios, local excursions in the flap bending moments could be correlated to the unsteady aerodynamic effects of the reverse flow regions on the retreating sides of the rotor disks. The improved comprehensive analysis modeling capabilities will be helpful to quickly assess the rotor dynamic response and its aerodynamic sources, including the effects of lift offset and rotor-rotor interactions, and so they will prove instrumental in the understanding of the steady and vibratory loads in the present test article as well as future coaxial rotor designs.