Vortex dynamics in the wake of a finite span wing in stable stratification.

A numerical investigation is carried out to study the evolution of wing-tip vortices in a stably stratified environment. Earlier studies have mostly modeled the wake behind a wing using a pair of counter rotating vortices (Spalart 1996, Ortiz et al. 2015).  In the present work we simulate the  full wake behind a finite span wing upto a downstream distance of 60 chord lengths for various levels of stratification. In the unstratified case, nearwake consists of the vortex rollup and far wake consists of fully developed wing-tip vortices (Navrose et al. 2019). The calculations are carried out at Re (Reynolds number)=1000 and  1≦ Fr (Froude number) ≦ 10. The results show that as strength of stratification increases, the rollup process of wing-tip vortex formation is inhibited. The stratification suppresses the vertical motion and baroclinic vorticity of opposite sense as that of wing-tip vortices is generated that persists along with vortex sheet. At relatively large stratification elongated flat 'V'-shaped structures are observed in the near wake. The far wake in this case comprises of a mixture of pancake like strutures (Pal et al. 2017) and streamwise elongated vortical structures. The vortical structures appears to have a well defined wavelength in the streamwise direction.