A large-eddy simulation on a deep-stalled aerofoil with a wavy leading edge

摘要

A numerical investigation on the stalled flow characteristics of a NACA0021 aerofoil with a sinusoidal wavy leading edge (WIT) at chord -based Reynolds number Re., 1.2 x 10(5) and angle of attack alpha= 20 degrees is presented in this paper. It is observed that laminar separation bubbles (LSBs) form at the trough areas of the WIT, in a collocated fashion rather than uniformly/periodically distributed over the span. It is found that the distribution of LSBs and their influence on the aerodynamic forces is strongly dependent on the spanwise domain size of the simulation, i.e, the wavenumber of the WEL used. 'file creation of a pair of counter-rotating streamwise vortices from the WIT and their evolution as an interface/buffer between the LSBs and the adjacent fully separated shear layers arc discussed in detail. The current simulation results confirm that an increased lift and a decreased drag are achieved by using the WLEs compared to the straight leading edge (SIT) case, as observed in previous experiments. Additionally, the WLE cases exhibit a significantly reduced level of unsteady fluctuations in aerodynamic forces at the frequency of periodic vortex shedding. The beneficial aerodynamic characteristics of the WEE cases are attributed to the following three major events observed in the current simulations: (i) the appearance of a large low-pressure zone near the leading edge created by the LSBs; (ii) the reattachment of flow behind the LSBs resulting in a decreased volume of the rear wake; and, (iii) the deterioration of von-Karman (periodic) vortex shedding due to the breakdown of spanwise coherent structures.