Aerodynamic interaction mechanisms in typical wingtip-mounted tractor propeller configurations

The wingtip-mounted tractor propeller configuration has been extensively studied due to its great potential for improving wing aerodynamic performance. In the present work, the aerodynamic interaction mechanisms in typical wingtip-mounted tractor propeller configurations are analyzed in depth using the reformulated vortex particle method. The results show that the elliptical lift distribution over the entire wing is altered by the installation of the tip-mounted propeller. The lift coefficient increases with inboard-up rotation and decreases with outboard-up rotation. Three key aerodynamic interaction mechanisms, swirl recovery, slipstream distortion, and slipstream impingement, are investigated. The swirl recovery mechanism generated by the inboard-up rotating propeller positively contributes to the performance of downstream wing. For the outboard-up rotation, the propeller-induced downwash results in reduced lift and increased induced drag. The interaction between the propeller-induced spanwise velocity and the wingtip-induced crossflow results in slipstream distortion. At α = 0°, for either inboard-up or outboard-up rotation, the slipstream on the retreating side is moved toward the propeller axis and away from the propeller axis on the advancing side. With the change of the rotation direction and angle of attack, the slipstream geometry exhibits different features. The slipstream impingement induced by the propeller generates time-varying loads on the downstream wing at the blade passing frequency. The propeller-induced tip vortices start to bend close to the leading edge and their vorticity increases, and then the vortex tube begins to deform. A higher angle of attack results in larger fluctuations in the downstream wing's drag coefficient.