Numerical simulation of a Kármán vortex street in an unstably stratified flow

Abstract

Numerical simulation of a Kármán vortex street formation behind a circular cylinder in an unstably stratified fluid was performed. The influence of thermal stratification on the vortex wake characteristics at different Reynolds and Richardson numbers is investigated. The system of Navier–Stokes equations in the Boussinesq approximation, which accounts for buoyancy effects in an unstably stratified medium, is considered. The numerical solution was obtained by the finite difference method using a splitting scheme for physical processes. It is shown that in the presence of unstable stratification, vortex formation intensifies and the geometric characteristics of the Kármán vortex street change compared to a homogeneous fluid. It has been found that convective instability, caused by the density distribution, leads to the emergence of secondary structures in the vortex wake. It is shown that with an increase in the Richardson number, a qualitative restructuring of the flow occurs: from a regular Kármán vortex street to a complex chaotic regime with multiscale vortex structures.