An Investigation of Transitional Phenomena from Laminar to Turbulent Natural Convection using Compressible Direct Numerical Simulation

The transitional phenomena from laminar to turbulent natural convection and the development process inside the channel are investigated using compressible direct numerical simulation (DNS). Numerical method of Roe scheme with preconditioning and dual time stepping are used for addressing natural convection flows with large temperature differences, which are low speed but the densities are variable. The results are qualitatively well consistent with the experimental data [1] and the transition point can be accurately captured. In addition, the development process respected to time can be clearly identified for four stages, which are laminar, unstable process, reliminarization and turbulence. After reaching the quasi-steady state, it can be observed that the laminar, transition and turbulence coexist in the same flow filed. Most important of all, the transitional phenomena are naturally induced by the effects of interactions between the buoyancy and shear stress without adding any fluctuations at inlet. It means that the numerical scheme and physical model adopted in this study has the potential to be a universal case for estimating the accuracy of turbulence model because the characteristics of parameters-free and independence from inlet condition.