# Simulated air velocity near ceiling

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 July 1, 1999, 04:13 Simulated air velocity near ceiling #1 Apple L S Chan Guest   Posts: n/a Dear all I am running a CFD simulation for air coming out from a wall diffuser near the ceiling of a room. The simulated velocity near the ceiling is much greater than that from measuered value. That means viscous friction exerted by the ceiling had not been well modelled. In my CFD code, logarithmic law is used. Could any one please advice me how to get better simulated velocity near the ceiling? Thanks a lot! Apple Chan

 July 1, 1999, 21:13 Re: Simulated air velocity near ceiling #2 John C. Chien Guest   Posts: n/a (1). Was the initial flow field simulated properly? The air must be routed through a duct behind the outlet ( the diffuser). After going through the diffuser ( the outlet), there is a velocity distribution in three directions. (2). So, if the boundary condition is set at the diffuser exit, then the velocity distribution vx, vy, and vz must match the actual distribution first. (3). Even if there is only a thin slot at the diffuser exit, you still need to use the actual velocity distribution as the initial condition. (3). Then you need to have enough number of mesh points to cover the diffuser exit and the development of the wall jet (jet next to the ceiling wall).

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