A method for tail rotor aerodynamic force prediction under rotor interference based on coupled momentum source and blade element theory

Due to the influence of slip flow and wake, the tail rotor of a helicopter may produce strong unsteady aerodynamic force in its main rotor interference flow field, which may affect the helicopter control and lead to structural failure. Although the unsteady flow field simulation method can capture the details of the flow field, the calculation amount is large. Therefore, this paper presents a fast method of tail rotor aerodynamic force prediction based on coupled momentum source and blade element theory. The momentum source model takes into account the disturbance of the flow field of a main rotor to that of a tail rotor. The induced velocity of the tail rotor is extracted from the flow field, and its quasi-steady aerodynamic force is solved iteratively with the blade element theory. In order to verify the accuracy of the method, this paper carries out the prediction of the tail rotor's aerodynamic characteristics under the main rotor's interference with different sideslip angles. In the range of 0° to 30° sideslip angles, the error of the tail rotor's average pull coefficient obtained with the fast prediction method is 2.31% to 4.50% compared with the wind tunnel experiment. Compared with the experiment, the error of the unsteady flow simulation method using the sliding grid is -4.50% to 1.20%, but the calculation amount of the experiment is only 9.61%. In the forward flight state of a small sideslip, regardless of whether the rotor slip sweeps the tail rotor, compared with the tail rotor's average pull predicted with the unsteady flow simulation method, the error of the fast prediction method is -6.19% to 6.15%. The average value of the unsteady pull coefficient of a single blade and the peak value of the first and second order blade passing frequency are close to those of the unsteady flow simulation method.