Efficient Surrogate-based Optimization of the Aerodynamic Performance of a Contra-rotating Open Rotor Utilizing an Infilling Criterion

This study presents an efficient surrogate-based optimization (SBO) method of the aerodynamic performance of a contra-rotating open rotor (CROR). The objective was to maximize propulsion efficiency while reaching the target thrust coefficient at the cruise condition. To reduce the sample size and improve the optimization convergence speed, an infilling criterion was proposed based on the features of the interaction between the CROR front and rear rotors. The efficient front and rear rotors of the initial samples were selected and then combined to form the infilled samples. The results show that the infilled samples were closer to the Pareto front than the initial samples. For the six optimization parameters, 20 initial sample points were used, 11 samples were infilled, and the surrogate-based optimization was completed in five iterations. In total 43 samples were calculated during the optimization. The number of overall samples is approximately seven times the number of optimization parameters. The optimization results in parameter changes compared to the baseline and improved propulsion efficiency while meeting the thrust target. The optimization process increases the torque share of the rear rotor and changes the flow state at different radial positions, leading to a more uniform total pressure distribution at the outlet position, both circumferentially and radially.