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Trying to visualize amount of turbulence in airflow

Trying to visualize amount of turbulence in airflow

Trying to visualize amount of turbulence in airflow

(OP)
I was told recently that ribbed tubing can have the effect of decreasing the effective diameter of a tube by as much as 50% due to drag.

I'm trying to form a mental image of the amount of turbulence and laminar flow in a tube, and how much the drag could be reduced by smoothing the ID of the tubing. It's just an interest I've been obsessed with lately. I've done a lot of searching on the web and at my library and can't find what I'm looking for.

My tube is about 3"x5" in diam, airflow is up to 167 mph I estimate and the volume of air is about 600 CFM max.  In the corrugated region There are 10-15 depressions about .25" apart and .25" deep.  I figure I should be able to easily reduce the depth of the corrugations to about 1/20th their current size.

Let me try to draw a picture:

--------------^^^^^^^^^^^^---------------------
                                          | valve
Airflow>>>                            ))))) obstruction
                                          | valve
--------------^^^^^^^^^^^^---------------------
Smooth walls   Corrugated
                  region

The "ribs" in the corrugated region resemble the top line in my diagram. They begin at the inside wall and go outwards about .25" (they don't reduce the internal area for airflow, they actually increase it a little bit.) I guess you'd actually call them elongated pits rather than raised ribs. Ok?
I found a book on basic fluid mechanics at my library. It was the most basic book on the subject they had. Although it's full of equations, and not as much calculus as the more advanced books, it seems my example is too simple, or unusual. I can't find anything even remotely similar in the book, or online.
I understand the basics of how the eddies and laminar flows in the tube behave, I'm just trying to get a feel for the change in "size" or amount of turbulence in the tube if I can smooth out the corrugations. If I could measure the airflow or a pressure change I would but I don't have that capability. All I have is the few numbers I mentioned above. I have no experience doing anything like this so I'm having a hard time visualizing the change in airflow caused by a given change in tube structure. I hope I made myself clear enough. Thanks.

RE: Trying to visualize amount of turbulence in airflow

Dude that's good ASCII artwork!

Flow visualization is a sub-specialty of fluid mechanics and there are people who devote entire careers to it.  There should have been some info on that in the textbook you saw.

As far as I know, most of the time some type of colorant is introduced into the flowstream, like dye (liquid) or smoke (gas), to try and make it follow the eddies and turbulence.  There are also laser and other light-manipulating methods used.  That is WAY oversimplified, but it is a starting point.  Do a Google search on flow visualization.

Thanks!
Pete

RE: Trying to visualize amount of turbulence in airflow

(OP)
Unfortunately, the entire system is contained in opaque tubing and I can only get in to make changes when the system is shut down and dismantled.  Thanks anyway.

RE: Trying to visualize amount of turbulence in airflow

...ok, then the thing to do would be to make a model using transparent tubing?  Using hydraulic similitude you should be able to reproduce your conditions at a lower rate/same Reynolds number, I'd think, to get a realistic representation of the flow at actual conditions.  

Or, since this is air at the conditions you describe, it's a low-pressure system, yes?  You could make a full-scale model from Lexan to do your visualization.

Thanks!
Pete

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