Insight into the impact of fixed transition on the aerodynamic performance and noise of airfoils with varying airfoil thicknesses

To explore the effect of surface pollution on the aerodynamics and acoustics of airfoils, the aerodynamic performance and noise of Delft University of Technology (DU) airfoils with different relative thicknesses are simulated using the shear-stress transport k-ω model and large Eddy simulation. The sensitive positions of fixed transition for DU airfoils are examined in terms of aerodynamic performance and noise, and the variations in aerodynamic performance, noise, and internal flow are analyzed. The results show that the sensitive position of fixed transition is almost unaffected by the relative thickness of airfoils. In terms of aerodynamic performance and noise, the sensitive transition positions on the suction surface are located at 1%c and 5%c, respectively. Fixed transition leads to a reduction in the aerodynamic efficiency and an elevation in noise. The impact of fixed transition on the airfoil's trailing-edge noise far exceeds its effect on radiated noise. The original airfoil's noise exhibits a typical dipole-like directional distribution. However, after the fixed transition, the dipole distribution gradually blurs, and this trend becomes more pronounced with increasing relative thickness. Fixed transition reduces the stability of wake vortex shedding and increases the energy loss, and an increase in relative thickness enlarges the high vortex region and vortex size near the fixed transition.