How does CFX-5 calculate the fluid specific general momentum source in Eulerian multiphase flows?


The fluid specific momentum sources in multiphase flows are defined in CFX-Pre or CCL as follows:

FLOW:
DOMAIN: Domain 1
SUBDOMAIN: Subdomain 1
FLUID: Air at 25 C
SOURCES:
MOMENTUM SOURCE:
GENERAL MOMENTUM SOURCE:
Momentum Source X Component = 10 [kg m^-2 s^-2]
Momentum Source Y Component = 0 [kg m^-2 s^-2]
Momentum Source Z Component = 0 [kg m^-2 s^-2]
Option = Cartesian Components
END
END
END
END
END
END
END


The source term for a cell is calculated by integration over the whole control volume and then applied to transport equation of the momentum equation of the phase. If the volume fraction of the phase goes to zero, the momentum of this phase may increase unphysically. Therefore we recommend to multiply the source term with volume fractions. If you don't multiply with the volume fraction, you have to take care in another way , that the source term is limited, if the volume fraction goes to zero.





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