A modification of the k-omega shear-stress-transport turbulence model is presented in this paper with the aim to improve the simulation of flows at a low Reynolds number. For this purpose, the incompressible flow at Reynolds number 6 x10^4 , around the Selig–Donovan 7003 airfoil, is investigated by using several turbulence models. The focus is placed on the k-omega shear-stress-transport turbulence model: a model very reliable for transonic flows but for which the application to low-Reynolds-number flows has been questioned. The limits of this model are analyzed in detail. The simulation of the laminar bubble arising on the SD 7003 airfoil has been remarkably improved by the proposed modification. In addition, the accuracy of the k-omega shear-stress-transport turbulence model has been preserved in the transonic regime at a high Reynolds number, as shown by the simulations of the flow around the RAE M2155 wing. Large-eddy simulations of the flow around the Selig–Donovan 7003 airfoil have also been performed and presented in the paper. The large-eddy-simulation data are used as a reference for the results achieved by the Reynolds-averaged Navier–Stokes method. The computed aerodynamic coefficients are compared with some available experimental data

The effectiveness of the riblets, one of the most interesting drag-reduction device, is discussed in this paper. Numerical simulations by the Reynolds-averaged Navier–Stokes equations with the riblets properly taken into account are presented. Riblets are modeled as a singular roughness problem by modifying the classical Wilcox boundary condition for rough walls. The boundary condition is able to predict the flow features in the low roughness range (transitional roughness) where riblets operate. A brief discussion of the simulations performed to validate the model is first presented. Then, a complex wing–body configuration is analyzed, and the overall effect of riblets on the aerodynamic coefficients is evaluated. Calculations of a complete aircraft configuration at transonic conditions show how a proper optimized choice of the riblet height can significantly improve the drag reduction.