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Air flow inside tubes Rough VS Smooth

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I have done some basic tests with air being sucked through tubes rough and smooth with rough and smooth inner cores and measuring the head of water at the suction end of a 1400 watt vacuum cleaner with all filters removed.


I just wanted to see what effect it has on a engine intake manifold there are some interesting side effects too so don't do it.



Outer tubes 42 mm ID 590 mm Length.

Inner tubes 33 mm OD 340 mm + 60 mm sticking out and caped off at outside end to increase suction head.

A 4.5 mm gap concentric between tubes provided by 3 screws at each end.

1 outer tube roughed up by wire wheel and 1 inner tube as well.

The clear tubing and measurement is on a 62.54 deg slope my bench is too high.



The results of my experiment.

Rough outer tube and smooth inner = 333 mm H2O head.

Rough outer and rough inner = 398 mm H20 head.

Smooth outer and smooth inner = 355 mm head.

Smooth outer and rough inner = 412 mm head.


I have made the rough outer tube slightly larger but the head difference is 6.6 %

I have made the rough inner tube smaller as well but it faired worse in the tests.


Would I have to measure the difference inside the tubes and adjust my figures some how?


Why does the rough inner tube have more head thus less air flow when compared to smooth inner tube?


Do small eddie currents in the boundary layer help air flow inside a tube? but why does it impede the flow when the inner core is rough and not the outer core?


What are the short comings of my test methods?


I have sound recordings of the air going into my engine intake and they sound different to other engines so i'm looking for reasons why, Ive done lots of searching on the subject but haven't found much, I'm I looking in the wrong places?


I have some sound recordings taken six years ago a a few recently I have a portable cam now and am comparing other engine sound wave forms from youtube, one thing I have noticed is there seems to be more harmonics in my recordings but that maybe because I was using a mic not attached to an AGC circuit like in a camera I will make a few more and compare them.


You can listen to my engine if you like its at Engine sounds

I have been putting various engine sounds through filters and looking at wave shape and duration but I don't really know what the difference is.

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