CFD Online Discussion Forums

CFD Online Discussion Forums (
-   Fluent UDF and Scheme Programming (
-   -   Problem with Mass source, Momentum source theory (

diffo August 20, 2009 06:10

Problem with Mass source, Momentum source theory
Intending to model an inlet (nozzle) that is smaller than a cell in a domain, i decided to define a mass source in the cell where my inlet is supposed to be, and to add to that mass source a momentum source.
Hence I expect to rebuild the given nozzle mass flow (m_dot).

Mass source UDF: m_dot/Volume _Cell
Momentum source UDF: m_dot*Exit_Velocity/Volume_Cell

m_dot: known from the details of the nozzle
Exit_Velocity: calculated by dividing m_dot with Air_density*Exit_Area_Nozzle

on a velocity Plot of a surface crossing the chosen Cell i see a velocity distribution, where the maximum velocity is though a the chosen cell, but the amount is not near that what i had implemented (implemented Velocity was "Exit_Velocity").

THE HINK in the logic:
according to the Fluent-user-guide (page 7-225) it is possible to create a mass source term (m_dot) without giving it any impuls, then create an impuls(Momentum) source term that orientates the mass.
But i u look carefully at the formula of the mass source, there is already a velocity in there (logically). Then i give in Momentum source a second velocity... from there on , I'm lost.

To make things easy, i chose a cell with Faces, that all have an area of 1mē.

Can someone please give me a clue how to manage to have a plotted maximal velocity that corresponds to implemented one....

All times are GMT -4. The time now is 03:19.