FACTORS OF AIRFLOW DISTRIBUTION FROM SYSTEM CEILING AIR DIFFUSERS AND ITS UNSTRUCTURED FINE ELEMENTS CFD SIMULATION

Abstract

Computational Fluid Dynamics (hereafter, CFD) is one of the most useful techniques to predict the airflow distribution in air-conditioned and ventilated rooms. The previous studies show that the prescribed velocity method (hereafter, P. V. method) is effective to simulate complicated airflow from an air diffuser in CFD. However, the velocity distribution in the vicinity of the air diffuser as boundary conditions of coarse gird CFD using P. V. method can be affected by the airflow rate, the connecting conditions of the diffuser and supply air duct, and the buoyancy effect due to the temperature distribution.In this paper, the development of the versatile airflow data for P. V. method and the method for its application are discussed. In the first study, the unstructured fine elements CFD simulations under isothermal condition are carried out and the obtained airflow distributions of the system ceiling air diffuser are compared. The relationship between the airflow rate and the velocity near the diffuser, the influence of connecting conditions of the diffuser and air duct are confirmed by the comparison of CFD results. In the second study, the influence of the buoyancy near the diffuser is compared to the inertial force of discharged air on the basis of local Archimedes number obtained by the unstructured CFD simulations under non-isothermal condition.