The DDES around Wing Based on Improved Mixed Length Scale

Abstract

For the separation problem at small and medium angles of attack, in the early stage of DDES (Delayed Detached Eddy Simulation) method, it takes some time for the flow separation region to develop, and usually delays the switch from RANS mode to LES mode, so as to underestimate the flow separation. An improved RANS-LES hybrid length scale method is adopted to modify the grid scale and vortex tilting measure (VTM) function in this paper. Based on open source CFD software OpenFOAM, the modified hybrid grid scale, vortex tilting measure(VTMnew) function and two-dimensional shear layer identification function FKH(VTMnew)are implanted into the S-A DDES model to study the flow around NACA0012 airfoil at high angle of attack and NACA0012 half span rectangular wing at angle of attack 12°. The vortex structure and tip vortex in the leeward region of the wing calculated by the original S-A DDES and the S-A DDES turbulence model with improved RANS-LES mixing length scale are compared. The results show that the rapid instability of the shear layer can be observed in the leeward region of the wing by using the proposed method, and the large-scale unsteady vortex system structure and the formation details of the wing tip vortex in the leeward region can be simulated more finely, which can effectively speed up the switching from RANS mode to LES mode of DDES method. In addition, the separated flow problem of the rectangular wing at angle of attack 18° is calculated, which further verifies the effective adaptability of the proposed method.

Keywords

• |ddes|unsteady flow|rans|les|wing tip vortex|openfoam|aerodynamics