Hi,
i know the total pressure difference between inlet and outlet give me a total pressure drop in system, but we have 4 type of pressure drop in a system. gravitational, accelerational, frictional and form resistance. how i can find or see the frictional pressure drop in ansys fluent? or how i can set the frictional factor?
frictional pressure drop can find from darcy formula with moody diagram. i want to know can i set a frictional factor for pressure drop in ansys fluent or no?
regards,
Mo,Movaffagh
Dear Mohammad Movaffagh
You can set a frictional factor.
But, at first, you must calculate roughness with the help of the frictional factor and set it on Fluent.
You can watch this video https://www.youtube.com/watch?v=G2v1KxWhSYU.
7:40 - Surface Roughness Modelling
Regards
Andrii Rogovyi
hello andrii
thank you for your response
you mean the roughness in wall boundary condition related to frictional factor?
another question is about the difference between total pressure inlet and total pressure outlet. their difference give me frictional pressure drop or not? i read many forum and they said that difference give us frictional pressure drop.
now i set roughness coefficient zero on the wall BC and i have a pressure drop which is near to frictional pressure drop. how it can be possible if i set the roughness coefficient to zero and my pressure drop is near to real answer??
regards,
Mo.Movaffagh
Dear Mohammad Movaffagh
1) Yes it's. The roughness in wall boundary condition is related to the frictional factor.
2) The difference between total pressure inlet and total pressure outlet is total pressure drop in system.
3)frictional pressure drop is not only roughness but also friction between liquid layers. "If you set the roughness coefficient to zero your pressure drop was near to real answer". What was the roughness coefficient in your real answer?
Regards
Andrii Rogovyi
thank's andrii
in steady-state model my friction factor is 0.022. i calculate the frictional pressure drop by Darcy formula ( delta p = (fL/D)(0.5*rho*v^2)). with out using the roughness coefficient, the theoretical frictional pressure drop was near to difference between total inlet-outlet pressure. now im confused.
Ansys fluent used this relation for total pressure:
p(total)=p(static)+p(dynamic)
how it can be equal with Darcy formula???
if total pressure difference is equal to frictional pressure drop how the ansys calculate other pressure drop terms?
you know the system pressure drop= frictional pressure drop((fL/D)(0.5*rho*v^2))+ elevation pressure drop(rho*g*h)+ acceleration pressure drop(0.5*rho*v^2)+ sudden expansion pressure drop
(see the pictures please)
how we can separate these terms in fluent?
regards,
Mo.Movaffagh
Dear Mohammad Movaffagh
If you want to separate pressure drops you can calculate in Fluent flow without rho change and without g. (rho = const and g=0).
Darcy formula uses static pressure and static pressure drops. In the pipe, with a constant diameter, we have not velocity change and rho*V*V/2 is constant.
If you calculate liquid with no change of rho you also can use g=9.81 and calculate rho*g*h separately.
If you have the friction factor of 0.22 it means that you have some roughness or laminar regime or smooth pipe regime. It means that roughness exists but does not influence a frictional factor.
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