if i did not set the boundary condition in gambit ,can i set the boundary condition in fluent?how do that?

Hi, As u said, yes you can define BC in fluent. If you do not define BC in Gambit, by DEFAULT it takes as WALL BC to each of the edges (for 2-D problem) or faces (for 3-D problem. you go to Define BC in Fluent, choose that FACE/EDGE (left panel)& on the Right side pannel you option of BC. if you want to define Vel Inlet, just click on Vel Inlet. 1 msg window will ask you to change BC. You choose YES. then you will get your desired BC on that EDGE/FACE.

thanks you very much!you did not understand my problem. i mean add boundary condition not modify boundary condition ?anyone can help me?

If yoy dont set any bc in gambit, then gambit will set a default wall bc for every face. But you can change them later in fluent, like dev said...

cheers