A fast multiobjective optimization method for S-duct scoop inlets considering both inflow and outflow is developed and validated. To reduce computation consumption of optimization, a simplified efficient model is proposed, in which only inflow region is simulated. Inlet pressure boundary condition of the efficient model is specified by solving an integral model with both inflow and outflow. An automated optimization system integrating the computational fluid dynamics analysis, nonuniform rational B-spline geometric representation technique, and nondominated sorting genetic algorithm II is developed to minimize the total pressure loss and distortion at the exit of diffuser. Flow field is numerically simulated by solving the Reynolds-averaged Navier–Stokes equation coupled with k–ω shear stress transport turbulence model, and results are validated to agree well with previous experiment. S-duct centreline shape and cross-sectional area distribution are parameterized as the design variables. By analyzing the results of a suggested optimal inlet chosen from the obtained Pareto front, total pressure recovery has increased from 97% to 97.4%, and total pressure distortion DC60 has decreased by 0.0477 (21.7% of the origin) at designed Mach number 0.7. The simplified efficient model has been validated to be reliable, and by which the time cost for the optimization project has been reduced by 70%.

A mono tiltrotor (MTR) design which combines concepts of a tiltrotor and coaxial rotor is presented. The aerodynamic modeling of the MTR based on blade element momentum theory (BEMT) is conducted, and the method is fully validated with previous experimental data. An automated optimization approach integrating BEMT modeling and optimization algorithms is developed. Parameters such as inter-rotor spacing, blade twist, taper ratio and aspect ratio are chosen as design variables. Single-objective (in hovering or in cruising state) optimizations and multi-objective (both in hovering and cruising states) optimizations are studied at preset design points; i.e., hovering trim and cruising trim. Two single-objective optimizations result in different sets of parameter selections according to the different design objectives. The multi-objective optimization is applied to obtain an identical and compromised selection of design parameters. An optimal point is chosen from the Pareto front of the multi-objective optimization. The optimized design has a better performance in terms of the figure of merit (FM) and propulsive efficiency, which are improved by 7.3% for FM and 13.4% for propulsive efficiency from the prototype, respectively. Further aerodynamic analysis confirmed that the optimized rotor has a much more uniform load distribution along the blade span, and therefore a better aerodynamic performance in both hovering and cruising states is achieved.

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Compared with single rotor helicopter, aerodynamic theoretical model for intermeshing rotor is immature. Aerodynamic modeling for intermeshing rotor is much more complex because of the strong and unsteady interference resulting from two closely rotating blades. Moving Overset Grid technical has been used for the aerodynamic investigation of intermeshing rotor in hovering state. SST k - ω turbulence model was used for the solving of unsteady RANS equations. The simulated result matches well with the experimental data, in which the calculation error for lift coefficient, Ct , is smaller than 4.5%. Firstly, the fluctuation of Ct is periodic with a frequency of 4/rev, which is equal to the total number of blades of the intermeshing rotor. Average aerodynamic loads rise as the increasing of collective angles. Secondly, the maximum induced velocity of the intermeshing rotor is significantly larger than those of the single rotor and the equivalent rotor. Blade-vortex interference and vortex-vortex interference coexist in the flow field of the intermeshing rotor. Finally, three shaft angles, 20°, 24°, 28°, were investigated. Among the calculating cases, the effect of the shaft angles is not monotonous. Maximum hovering efficiency is achieved at θ = 24°.