[zdunol]

Hello,

I'm considering a pipe of 6.4 (1/4") diameter with glycol-water solution flowing at v=0.5 m/2 and I was wondering if the flow will be laminar.
Hands on calculations show that bulk Reynolds number is equal to 500 so it should be fine, but I was worried about high (bulk)velocity = 0.5 m/s so I createad a very ver very simple setup where I considered 0.5m long pipe of this type.

Simulation went smoothly, XY plots at the outlet showed nice quadratic velocity distribution, I wanted to check out Cell Reynolds number distribution at the outlet and It does not look like a quadratic equation It looks a little bit like a quadratic eq. but it bends a little bit to the inside, so the whole thing resembles a smooth T tetris-shape (I hope you know what I mean)
In the centerline the velocity is 0.9 m/s,

So, am I facing a transitional regime in here guys, do you think I should refine the mesh, use double precision solver or let the simulation run longer?
Shouldn't the velocity distribution be similar to Cell reynolds distribution?
btw does anybody know what is typical roughness of silicone tubes?
Kind regards,
Zdunol

[FMDenaro]

Originally Posted by zdunol

Hello,

I'm considering a pipe of 6.4 (1/4") diameter with glycol-water solution flowing at v=0.5 m/2 and I was wondering if the flow will be laminar.
Hands on calculations show that bulk Reynolds number is equal to 500 so it should be fine, but I was worried about high (bulk)velocity = 0.5 m/s so I createad a very ver very simple setup where I considered 0.5m long pipe of this type.

Simulation went smoothly, XY plots at the outlet showed nice quadratic velocity distribution, I wanted to check out Cell Reynolds number distribution at the outlet and It does not look like a quadratic equation It looks a little bit like a quadratic eq. but it bends a little bit to the inside, so the whole thing resembles a smooth T tetris-shape (I hope you know what I mean)
In the centerline the velocity is 0.9 m/s, Re=~2000

So, am I facing a transitional regime in here guys, do you think I should refine the mesh, use double precision solver or let the simulation run longer?
Shouldn't the velocity distribution be similar to Cell reynolds distribution?
btw does anybody know what is typical roughness of silicone tubes?
Kind regards,
Zdunol

but you did not consider the fact that the Rex (Reynold number based on the axial position) increases along the pipe.

furhtermore, I do not understand the question about the cell Reynolds number, it depends on the grid size.

[zdunol]

yeah but I check Rex at outlet so x=const,
I didn't know that cell reynodls number depends on the size of cell, sorry for silly question

[FMDenaro]

Originally Posted by zdunol

yeah but I check Rex at outlet so x=const,
I didn't know that cell reynodls number depends on the size of cell, sorry for silly question

the cell Re number is just a measure of the resolution reached by your grid...when Reh=O(1) that means you solve convection and diffusion of the momentum at the same level of resolution. When Reh > O(10) you are not able to solve small structures