# Reynolds Number in Fully Developed Turbulent Flow

Abubakar
Member
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**47**Hi,

I was going through the problem statement of the Fully Developed Turbulent Flow challenge which is there in the Vicous Laminar flows course.

As in the problem statement the pressure gradient was given quantity but then how did we calculate Re from pressure gradient? Is the Re was also a given quantity?

Thank you,

Abubakar khan

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## Comments

3,177AdminHello,

In this case, we obtain the Re number from the flow solution (average velocity of the fully developed flow). It is presented in this manner to justify the usage of a turbulence flow model to solve this problem.

Karthik

141MemberUnderstood @Kremella sir.

One more question sir, since in this case the Re was not known, then who we will decide the length of the pipe?

141MemberAlso, sir can you please tell me the what value of static pressure and length we have taken to find this -1 Pa/m pressure gradient? TIA

3,177AdminHello,

The length of the pipe is normally chosen based on the requirement - say you are transporting something from one location to another, you will need a certain length. Another option for this choice is the overall pressure drop experienced by the flow. Because you will then need to size a pump to deliver a positive head to overcome this pressure.

This is just a canonical problem selected to explain the concept of fully-developed flow using a simulation. In this case, we are simply taking a small arbitrary length across which we know the pressure drop. We are forcing the flow at the outlet back into the inlet using the periodic condition to let the flow become fully developed.

I hope this helps.

Karthik

141MemberThank you so much @Kremella sir, for this brief explanation.