[MissCFD]

What is the meaning of "update mass flux" in the processus of segregated and coupled algorithm ?

https://www.sharcnet.ca/Software/Flu...ug/node987.htm

Thank you very much

[LuckyTran]

At the start of each iteration you have initial fields for all the variables. After you solve the momentum equations, you have an updated velocity field.

In each of the transport equations there are advective terms (since energy, species, etc. are advected by the velocity field). But also note that the momentum transport equation is also a transport equation.

You have a choice of solving these transport equations using the initial field or the newly computed velocity field. If you choose to use the newly computed field then you must update the fluxes at each cell with the new velocity & pressure field. The previous fluxes just used to solve the momentum transport equation are thus "updated" with the newer fluxes. Once you have solved the momentum equation there's no need to work on the old fluxes, hence there is no need to keep track of two sets of fluxes. You can simply overwrite/update the initial fluxes with the new fluxes.

[MissCFD]

Thank you for your response. I understand better the process now.

But what is exactly "mass flux" in practical terms ?
Because in the segregated process, it is noted "update mass flux, pressure and velocity".

Is it the update of continuity equation ?
Or is it the update of the quantity rho x Q ?

Originally Posted by LuckyTran

At the start of each iteration you have initial fields for all the variables. After you solve the momentum equations, you have an updated velocity field.

In each of the transport equations there are advective terms (since energy, species, etc. are advected by the velocity field). But also note that the momentum transport equation is also a transport equation.

You have a choice of solving these transport equations using the initial field or the newly computed velocity field. If you choose to use the newly computed field then you must update the fluxes at each cell with the new velocity & pressure field. The previous fluxes just used to solve the momentum transport equation are thus "updated" with the newer fluxes. Once you have solved the momentum equation there's no need to work on the old fluxes, hence there is no need to keep track of two sets of fluxes. You can simply overwrite/update the initial fluxes with the new fluxes.

[LuckyTran]

Originally Posted by MissCFD

Thank you for your response. I understand better the process now.

But what is exactly "mass flux" in practical terms ?
Because in the segregated process, it is noted "update mass flux, pressure and velocity".

Is it the update of continuity equation ?
Or is it the update of the quantity rho x Q ?

It is not referring to solving the continuity equation. Solving the continuity equation is part of the pressure-velocity coupling scheme, SIMPLE/PISO/COUPLED. Updating the mass flux refers to updating the rho x u, rho x v, and rho x w at each face at each cell. The mass fluxes at cell faces are needed to solve the transport equations (like energy or species transport).

If there were no additional transport equations (i.e. only continuity & momentum, no energy & no species), then you wouldn't need to update the mass flux per se. You would have to update the mass fluxes at some point before the next iteration to setup the momentum transport equation.