Why Does the Velocity Profile in a Pipe Show a Dip at the Center?

[pavadrin]

ive have recently conducted a lab for investigating the behaviour of fluids in a pipe system
the fluid chosen was an oil with a density of 853 kg m-3

i used pitot-traversing gear to measure the pressure at different positions from the wall of the pipe (to the centre and then assumed a mirror image beyond the centre of the pipe). i have come to plot these values on the graph and have had unexpected results. i have checked over these many times, and according to the values this is the velocity profile i obtain:

http://img133.imageshack.us/img133/9461/velocityprofilefortest0n.jpg

whats causes the dip at the centre of the pipe? is this cause by turbulent flows? or have i simply got the wrong results? i have checked with others whom i conducted the experiment together and obtain similar results, so if the results are incorrect there may be something wrong with the equipment. or is this simply a phenomena of some sort?

any suggestions would be of immense help
many thanks, pavadrin

 

[Jhero]

Dear Pavadrin,

Thank you for sharing your results with us. The dip at the center of the pipe is a common phenomenon observed in fluid flow experiments and is not necessarily an indication of incorrect results. This is known as the "centerline dip" or "core flow dip" and is caused by the presence of turbulent flow in the pipe.

Turbulent flow is characterized by chaotic and irregular motion of fluid particles, which can lead to variations in pressure and velocity within the flow. In your experiment, the oil is flowing through the pipe at a high velocity, which can cause turbulence to occur.

The dip in the velocity profile is a result of the turbulent eddies that form at the center of the pipe. These eddies create a region of low velocity, which is reflected in the dip in the velocity profile. This phenomenon is more prominent in pipes with larger diameters and higher velocities.

To confirm if this is indeed due to turbulent flow, you can perform further experiments at different flow rates and pipe diameters. If the dip is consistently present, then it is most likely caused by turbulent flow.

I would also suggest checking the calibration of your equipment to ensure accurate measurements. You can also try using different types of fluids with varying densities to see if the dip in the velocity profile changes.

I hope this helps and good luck with your further experiments!