An iterative free-wake computational method is developed for the prediction of aerodynamic interaction characteristics between the twin rotors of a tandem helicopter.Here the mutual interaction effects between twin rotors are included,as well as those between the rotor and wake.A rotor wake model,blade aerodynamic model and rotor trim model are coupled during the process of solution.A new dual-rotor trim approach is presented to fit for the aerodynamic interaction calculations between tandem twin rotors.By the present method,the blade aerodynamic loads and rotor performance for the twin rotors under the interactional condition are calculated,and the comparisons with available experimental data are also made to indicate the capability of the proposed method.Then,the effects of such parameters as the longitudinal separation and axial separation between twin rotors on the aerodynamic interaction characteristics are analyzed.Based on the investigation,the conclusions are obtained to be of benefit to the configuration design of tandem rotors.Furthermore,the performance comparison between the tandem rotors and a single rotor is conducted.It is shown that the strongest interaction does not appear in a hover state,but in a low-speed forward flight state.
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