Modelling of a supply air terminal for room air flow simulation.

The paper discusses methods to set boundary conditions at the air supply opening in predictions of room air flows with computational fluid dynamics. The work is a part of the International Energy Agency project "Air Flow Patterns within Buildings", Annex 20. The air supply terminal in the Annex 20 project is a commercial diffuser which creates a stagnation region and a complicated wall jet below the ceiling. Fairly well predictions in the wall jet region were obtained replacing the diffuser by a simple opening which has the same momentum flow as in the diffuser. The momentum flow was well known which is not usual for complicated diffusers. In the initial section of the jet, the numerical method causes unintentional and uncontrollable mixing, which resembles the diffusion properties of the actual diffuser. The simple opening case was also measured and the agreement with the diffuser case in the wall jet was found to be satisfactory. More advanced methods as the momentum method and the prescribed velocity method allow more freedom to modify the jet flow. They should be preferred in practice.