In this paper, numerical simulation study on characteristics of air jets flowed on cone was carried out, which mainly focused on the effects of cone vertex angles on airflow pattern. If the cone vertex angle is larger than the top value of a certain range of angles, the air jet will deflect up relative to the generation of cone. If the cone vertex angle is less than the bottom value of the range of angles, it will deflect down. The certain range of cone vertex angles was defined as critical angles in the paper. The study was conducted on two kinds of boundary conditions, one was confined jet which flowed out from the inlet located on ceiling and the other was free jet which flowed out from the inlet located in free space. For the confined jet, the cone vertex angles in range of 90 degrees similar to 120 degrees were considered, and for the free jet, the angles in range of 130 degrees similar to 170 degrees. The standard k-epsilon model of FLUENT was applied to solve in this study, and the near wall treatment was non-equilibrium wall function. The results showed that the critical angles were 101 degrees similar to 102 degrees for confined boundary condition, and 160 degrees similar to 170 degrees for free boundary condition. Furthermore, if the cone vertex angle was larger than the top value of the range of angles, the air jet deflected up, and if the cone vertex angle was smaller than the bottom value of the range of angles, the jet deflected down. The critical angles of cone were consistent with the Awbi's suggestion "the circular ceiling diffuser should not bigger than 120 degrees", under the confined boundary condition.
