# Fluid accelerate from inlet to outlet for straight pipe

Hi everyone

I am new to SimScale. I just finished a simulation for a straight pipe with a small obstruction at the center. The results shows the fluid accelerated from inlet to outlet which doesn’t sounds logical to me. I used zero pressure for the outlet, could it be the reason? I attached an image of the velocity contour. I appreciate your helps.

Regards,
Sina

Hi Sina!

Can you please share the link to your project, so we can have a detailed look at your setup and results?

Hi

Thanks for your quick reply. below is the link to simulation.
https://www.simscale.com/workbench/?pid=6739023084812691636&rru=65caacea-dfee-46df-8591-2a6fc2767c85&ci=40029c2f-97f9-4c90-b4be-de7303c38233&mt=SIMULATION_RESULT&ct=SOLUTION_FIELD

Hello @sghafoorpoor_y ,

Quickly stopping by to hopefully shed some light: the acceleration comes from a few of factors:

1. The currently inlet condition has an uniform velocity field of roughly 14 m/s
2. In reality, the velocity profile of a developed flow is not going to be uniform. As the boundary layer develops, the regions close to the wall will slow down. Since mass conservation needs to be satisfied, the regions towards the center of the pipe will accelerate. For an incompressible flow, the average velocity will still remain roughly 14 m/s
3. This is exactly what you see: velocities larger than 14 m/s are experienced at the center of the pipe to make up for low velocity regions close to the wall

If you search for “boundary layer pipe” (or similar combinations of words) in your favorite search engine, you should get more information and images for a better visualization.

Cheers

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