Air supply opening model of ceiling diffusers for numerical simulation of indoor air distribution under actual connected conditions, part I: Model development

When air distribution in a ventilated room is simulated with computational fluid dynamics (CFD), the duct connecting the air supply diffuser is usually assumed to be long enough that the outflow is fully developed when describing the boundary conditions of the diffuser. In fact, it was found that incompletely developed flow from an air supply diffuser does exist, as the space for duct installation is often limited in actual ventilation systems. In this article, a method for describing the boundary conditions of square and round ceiling diffusers under actual connected conditions is studied for indoor air distribution simulation with a CFD method. The numerical method to simulate the diffuser outflow under actual connections is validated and then applied for the study. Combined with similarity analysis, the controlling parameters and their influences are analyzed numerically. Based on the analysis and previous work, the N-point air supply opening models for square and round ceiling diffusers are improved for numerical simulation of indoor air flow under three common actual connected conditions, including a round elbow, a square elbow, and a three-way duct connection. The N-point model is represented in figures, indicating the nondimensional outflow velocity of each diffuser versus the controlling parameters.