Unsteady Reynolds averaged Navier–Stokes simulations of a buoyant plume above a cylinder

Unsteady Reynolds averaged Navier–Stokes simulations of a horizontal heated cylinder with Rayleigh number Ra = 9·4 × 10⁷ were carried out and compared with experimental data. Different one-point closure models were used, both two-equation turbulence models and more sophisticated Reynolds stress models. The results approach the laminar solution regardless of the model used, and thus turbulent effects that occur downstream of the cylinder are not captured and the ensemble averaged results differ significantly from the experimental results. Nevertheless, the simulations are examples of mainstay engineering approaches and illustrate possible problems and pitfalls when using commercial general-purpose computational fluid dynamics codes without comparison against experimental results or other means of verification. Natural convection heat transfer from a single horizontal cylinder at intermediate Rayleigh numbers is a well-examined classical problem within heat transfer research. However, even though the geometry is very simple, the problem involves rather complex flow features that are hardly amendable by Reynolds averaged Navier–Stokes simulations or even large eddy simulations.