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kamal August 22, 2008 15:20

Drag co-efficient
Hi! I am new in the task is to find Drag co efficient for the flow over the sphere in the pipe for differnt reynolds number 250 to 1000.sphere is in the center of the pipe and inlet condition of the pipe can be neglected and flow is fully devloped.i did modelling in the gambit for this pipe diameter is 0.2 m , length is 6 m and sphere diameter is 0 .035m.i specify velocity inlet as boundry condition.Can anyone help me how to specify reynolds number in the fluent.i calculate velocity of the water based on the reynolds number but it is almost zero.

Can anyone help me how to find Drag-coefficient for this problem ?

Regards, Kamal

Smith_K August 23, 2008 03:36

Re: Drag co-efficient
You cannot input Reynolds number directly into Fluent tool. You know viscosity of the fluid, density and inlet diameter using which you can find the inlet velocity for a particular Reynolds number. Input the velocity as the boundary condition. You custom field functions to calculate the coefficient of drag.

ashish August 23, 2008 05:06

Re: Drag co-efficient
i think if you keep periodic boundary condition in gambit(where we select wall etc.) fluent will ask you mass flow rate, pressure drop

by this you can set a desired Re no

one has already suggested the other way

do reply here so that we can learn as giving advice is easy !!

kamal August 23, 2008 12:50

Re: Drag co-efficient
Thank you very much smith.

I cannot understand what is custon field function to calculate Drag co efficient? i am new in fluent.i have one more question.for Finding reynolds number,do i need to specify the diameter of the pipe or diameter of the sphere and how can i find the stagnation angle?can you help me for that plz?? Thank you very much again.

kamal August 23, 2008 12:52

Re: Drag co-efficient
thanks ashish!

but i think in the fluent we can't directly specify the reynolds number.and can we give another boundry conditon other that velocity inlet for this problem??

ashish August 28, 2008 11:16

Re: Drag co-efficient
if you keep the periodic condition in gambit fluent will ask for the mass flow rate

you can convert Re no interpreting the velocity in terms of mass flow rate give as an initial condition

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