General momentum source velocity query

siw · November 25, 2021, 09:17

In CFX Modeling Guide section 1.3.2.2.2 it gives the equation: $S_{i}=-C\left(U_{i}-U_{i,spec}\right)$ for a general momentum source. $U_{i}$ must be the velocity components at a location as calculated by the solver, but what exactly is $U_{i,spec}$ ? This can be determined by Expressions, User Functions etc, but I don't think it can be consider as a 'specified' velocity. The Modeling Guide does not directly state this.

Thanks.

ghorrocks · November 25, 2021, 16:56

The U(i,spec) is the velocity you want to have at that point. It can be a constant, a function or anything. As it is the velocity you want, they call it the specified velocity. Does that explain it?

siw · November 26, 2021, 01:57

Thanks Glenn. I am writing a report and just wanted to state this parameter accurately and specified velocity will do nicely.

November 25, 2021, 09:17	General momentum source velocity query	#1
siw Senior Member Stuart Join Date: Jul 2009 Location: Portsmouth, England Posts: 746 Rep Power: 26	In CFX Modeling Guide section 1.3.2.2.2 it gives the equation: $S_{i}=-C\left(U_{i}-U_{i,spec}\right)$ for a general momentum source. $U_{i}$ must be the velocity components at a location as calculated by the solver, but what exactly is $U_{i,spec}$ ? This can be determined by Expressions, User Functions etc, but I don't think it can be consider as a 'specified' velocity. The Modeling Guide does not directly state this. Thanks.

November 25, 2021, 16:56		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,979 Rep Power: 145	The U(i,spec) is the velocity you want to have at that point. It can be a constant, a function or anything. As it is the velocity you want, they call it the specified velocity. Does that explain it? __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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November 26, 2021, 01:57		#3
siw Senior Member Stuart Join Date: Jul 2009 Location: Portsmouth, England Posts: 746 Rep Power: 26	Thanks Glenn. I am writing a report and just wanted to state this parameter accurately and specified velocity will do nicely.