CFD modelling of radiators in buildings with user-defined wall functions

• This paper studies how to deal with natural convective heat transfer for a radiator in order to simplify the simulations.
• By adding user-defined wall functions the number of cells can be reduced considerably compared with the k-ω SST turbulence model.
• Compared to manufacturer data the error of the model is less than 0.2% for the investigated radiator height and temperature.

The most widely used turbulence model for indoor CFD simulations, the k-ε model, has exhibited problems with treating natural convective heat transfer, while other turbulence models have shown to be too computationally demanding. This paper studies how to deal with natural convective heat transfer for a radiator in order to simplify the simulations, and reduce the numbers of cells and simulation time. By adding user-defined wall functions the number of cells can be reduced considerably compared with the k-ω SST turbulence model. The user-defined wall function proposed can also be used with a correction factor for different radiator types without the need to resolve the radiator surface in detail. Compared to manufacturer data the error is less than 0.2% for the investigated radiator height and temperature.