# Momentum source definition

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 December 21, 2009, 13:17 Momentum source definition #1 New Member   Join Date: Dec 2009 Posts: 2 Rep Power: 0 Good afternoon everybody, I'm trying to model a part of my mesh as a pressure loss by means of the usage of the equation of the loss itself. At this purpose, I have defined a subdomain. As subdomain has have defined exactly the model part I have to model a pressure drop. The way I wish to use for this drop specification is the following one: Dp = a*v^2 where: Dp is the pressure difference between the entry and the exit of my subdomain a is a constant I wish to define an expression of thje previous equation... but without success.... Then, I'm trying to define it as follow I open "Edit Subdomain" I enable "Sources" I enable "Momentum Source/Porous Loss Model" I enable "General Momentum Source" in order to setup the x component as Zero, the y component as zero and to consider for the z component, the expression I should have been already defined. How can I do? Thanks in advance for helping me Best Regards Davide

 December 21, 2009, 18:31 #2 Member   Join Date: Nov 2009 Posts: 49 Rep Power: 7 Hi, When using General Momentum Sources you have not to define the expression of the pressure losses , just indicate the value of the source in the Z direction if it is uniform in the domain else you should write the expression of the source versus Z (ex : S=aZ+b). Now, if you are interested by using this expression Dp = -a*v^2 you must use Directional Loss Model with these settings: Streamwise Direction > X Component 0 Streamwise Direction > Y Component 0 Streamwise Direction > Z Component 1 Streamwise Loss > Option Linear and Quadratic Coefs Streamwise Loss > Quadratic Resistance Coefficient (Selected) Streamwise Loss > Quadratic Resistance Coefficient > Quadratic Coefficient a

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