The article deals with the numerical simulation of unstable, incompressible flows with stratifications. The mathematical model is based on the Boussinesq approximation of the Navier-Stokes equations. The flow field in the towing tank with a moving cylinder is modeled for wide range of Richardson numbers. The obstacle is modeled via appropriate source terms. The resulting set of PDE is then solved by the fifth oorder WENO scheme, or by a second order finite volume AUSM MUSCL scheme. Both schemes are combined with the artificial compressibility method in dual time. and Obsahuje seznam literatury