problem with result, SolidWorks Flow simulation

Dear Flow Simulation Forum Members,

I am a new user of the Flow Simulation. I tried to use it to simulate the flow field of a circular air diffuser.

The dimensions of the room are 12m*12m*3m. The position of the diffuser is in the center of the roof. The inlet velocity is 5m/s.

 

The following are the results (velocity contour, horizontal and vertical views).

 

Since the shape of diffuser is circular and the shape of room is symmetric with diffuser’s axis, I think the results should be concentric circles around the center point. But it looks quite strange. Are these results right? Or I miss something when running Flow Simulation.

Hope someone can give me your opinions.

Thank you.

SolidworksFlow Simulation