Dominant geometric sensitivities and associated aerodynamic mechanisms of a co-flow jet airfoil

Abstract

Co-flow jet (CFJ) is an active flow-control technique with strong potential for lift enhancement, drag reduction, and separation suppression. However, the relative importance, influence directions, and aerodynamic mechanisms associated with CFJ geometric parameters remain insufficiently understood. In this study, Kriging surrogate models were constructed using Latin hypercube sampling. Sobol global sensitivity analysis and Spearman rank-correlation analysis were used to quantify the effects of geometric parameters on the maximum lift coefficient and maximum corrected aerodynamic efficiency at a jet momentum coefficient of 0.04. Controlled single-parameter computational fluid dynamics analyses were then conducted for representative parameter variations, followed by sensitivity-guided variable screening and multi-objective optimization. The results show that the injection-slot position dominates the maximum lift coefficient, whereas the suction-surface downward translation has the strongest influence on the maximum corrected aerodynamic efficiency. Moving the injection slot downstream improves near-wall momentum retention and delays suction-side separation. Although the suction-slot position has a weaker influence on maximum lift, it still affects separation onset and stall. Increasing the suction-surface downward translation reduces the power-consumption penalty at moderate angles of attack but weakens attachment near stall. The five-variable optimization retains performance close to that of the full six-variable model, while the four-variable model shows a more evident reduction in corrected aerodynamic efficiency. After optimization, the stall angle increases from 12° to 16°–17°, the maximum lift coefficient improves by more than 11%, and the maximum corrected aerodynamic efficiency increases by more than 44%.