Grid dependency of wall heat transfer for simulation of natural convection flow problems

In the indoor environment natural convection is a well known air flow phenomenon. In numerical simulations applying the CFD technique it is also known as a flow problem that is difficult to solve. Alternatives are available to overcome the limitations of the default approach (standard k-e model with standard wall functions) with respect to these type of flow problems. However these are not (yet) generally available. The paper discusses in a numerical study the grid sensitivity of the standard approach for a benchmark case and compares the results with two alternatives. The results indicate that in all cases sensitivity remains presents and that a fine near wall grid is unavoidable to arrive at results which are in line with experimental data. The discussion addresses some other alternatives and the use of empirical data. The latter still remains attractive for use in these type of flow problems, at least for reference.