# Mass Flux vs Velocity Inlet

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 July 18, 2005, 10:09 Mass Flux vs Velocity Inlet #1 Sandra Guest   Posts: n/a Hi, I am trying to impose a sinusoidal veloity profile at the inlet using a UDF. Reading more about it I realized that for my case (compressible case) the boundary conditions to be used should be mass flow inlets vs velocity inlets. Would anyone know the difference between the two. In another words can I use the same UDF for the mass flux, considering that mass flux is rho*u*A/A. I'm getting somewhat confused with the UDS for mass flux stories. I would appreciate any inputs. Sincerely, Sandra

 July 18, 2005, 12:01 Re: Mass Flux vs Velocity Inlet #2 Seeker Philip Guest   Posts: n/a Hi Sandra, I am using a similar setup. The correct option to use is the mass flux condition for a well posed solution. You can modify the UDF pretty easily to include the density (assuming no density variation). Phil

 July 18, 2005, 12:44 Re: Mass Flux vs Velocity Inlet #3 Sandra Guest   Posts: n/a Hi Phil, thanks for writing. I'm not sure what did you mean by mass flux condition for a well posed solution. The flow is compressible and I am using the ideal gas option.Did you just mean to multiply my UDF that I had written for the velocity profile by constant density?

 July 18, 2005, 14:31 Re: Mass Flux vs Velocity Inlet #4 Seeker Philip Guest   Posts: n/a Yeah... Thats right for a constant density at the inlet. Make sure you solve the enrgy equation as well if the flow is compressible. Phil

 July 18, 2005, 18:40 Re: Mass Flux vs Velocity Inlet #5 Sandra Guest   Posts: n/a Thanks. There is still something wrong. I've read a little bit about UDS and mass flux. Is that applicable. Would you know when and why would one use that.

 July 20, 2005, 13:09 Re: Mass Flux vs Velocity Inlet #6 Seeker Phil Guest   Posts: n/a I'm sorry... I'm not sure about that. Do you have any other details that might make it clearer?