taylorboosh
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Registered: 3rd Apr 07
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if we have a tube with a 40mm inner diameter which is 500mm long
and
another tube which has a 70mm inner diameter along the length but a 50mm long section at one end with a 40mm inner diameter (the 70mm tapers down to the 40mm smoothly), which is also 500mm long
both tubes are nice and smooth and made from similar materials and are the same shape (aside from the obvious)
i wish to then suck air through each tube... using a turbine which measures 40mm in diameter (obviously this only fits at one end of the tapered tube)
which tube will flow better and why?
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Russ
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Registered: 14th Mar 04
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smaller
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Rob E
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Registered: 1st Jan 06
Location: Madeley, Stafford....I want to live back in Wales!
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the second option, you will have a much smoother flow of air
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LeeM
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Registered: 26th Sep 05
Location: Liverpool
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difference will be negligible if youre using a turbine and sucking through
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Gary
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Registered: 22nd Nov 06
Location: West Yorkshire
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Id go with robs answer, he should kow these things.
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Russ
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I'd have thought that by using a tube that was thicker at one end than the other the air would be going faster through the narrower end which could cause problems with smoothness, where as if the pipe is the same shape you'd have a constant speed.
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Jake
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Registered: 24th Jan 05
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the thinner tube will flow better because the air pressure inside will be higher therefore less turbulance
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LeeM
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Registered: 26th Sep 05
Location: Liverpool
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surely it will depend on the power of the turbine, if its not strong enough to hit the max airflow of the 40mm pipe then yeah the pressure may be higher in the thinner tube but the volume of air being expelled out of the back of the turbine will be the same
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Rob E
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Registered: 1st Jan 06
Location: Madeley, Stafford....I want to live back in Wales!
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Here is a diagram of typical constant flow velocity through a plain pipe and a bellmouth pipe (the correct term for the pipe mentioned in the original post), the colour spectrum represents the rate of air flow where blue is static, up to red, which is maximum flow velocity.
Plain pipe end -
Belmouth pipe
You can clearly see the bellmouth pipe flows much more efficiently with very little turbulence. The plain pipe demonstrates a flow deficiency around the diameter of the pipe and thus creating a much less efficient air tract.
You see this kind of design used on a typical ITB setup like so -
High performance turbocharged engines use a similar design too -
If you are doing this for an assignment or similar in which it sounds very much like you are judging by the question you asked, I suggest researching "velocity stacks" 
[Edited on 22-11-2011 by Rob E]
[Edited on 22-11-2011 by Rob E]
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taylorboosh
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Registered: 3rd Apr 07
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Well a turbo charger is the turbine in question. I see your point about a bellmouth but... The bellmouth you depict is only larger at the end then uses a thin pipe for majority. The one i depict is larger all along with what id call a strangulation point?
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Russ
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I envisaged it the way you just said John.
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ed
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Registered: 10th Sep 03
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If the pipe has a constriction in it then you'll end up with high airspeed and low pressure. Is that what you want?
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taylorboosh
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Registered: 3rd Apr 07
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tbh its not an assignment ect its to do with these wider tips the vag people cream over
i had a higher flow tip on my golf and one on the tt which both made no differance (placebo effect if any at all), now they say these are better because theyre wider but i just can see how?
a. the filter will be able to flow more air than before?
b. the inlet side of the turbo can take in more air because its basicly a strangulation point?
c. if they really do work and flow much more air, shouldnt the map be optimized?
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taylorboosh
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Registered: 3rd Apr 07
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as you can see the red one is no wider at either end, so maybe may origional question was wrong?
its the same at each end but wider in the middle?
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AK
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Registered: 5th Jul 00
Location: Aberdeen City
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low pressure = high flow speed
Think of rear diffusers - they expand to lower the air pressure which helps smooth out, and draw air through the more constricted section.
Google 'Bernoulli'
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taylorboosh
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Registered: 3rd Apr 07
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yes but they dont flow into a bottle neck
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ed
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Registered: 10th Sep 03
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The red tube does though. You will get a decrease in pressure and an increase in velocity just as the air flows into the turbo. My simple mind wants to think that you'd want higher pressure air going over the turbine so that it can work more effectively, but in reality I don't know.
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adiohead
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Registered: 28th Sep 01
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I just bought a normal sized silicone tip for £70 and saved myself £50.
The recorded increase in g/s for the wider one is minimal and not worth the extra, imo
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taylorboosh
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Registered: 3rd Apr 07
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I only bought a silicone one because it looks well
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adiohead
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Registered: 28th Sep 01
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I got a black Autobahn88 one because I suspected my standard flimsy TIP was collapsing, turned out one of my new sensors had become faulty.....crappy Bosch 
I got mine from Japan and it appears to be the cheapest I've seen. Sod paying stupid amounts for a pipe.
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taylorboosh
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Registered: 3rd Apr 07
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Vag fags for you
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Rob E
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Registered: 1st Jan 06
Location: Madeley, Stafford....I want to live back in Wales!
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Sorry john, I misread what you were explaining, those pictures make it a bit more clearer.
It sounds more like its based on the helmholtz resonator effect. I haven't got time to explain it but have a read of this
http://www.brighthub.com/engineering/mechanical/articles/84316.aspx
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taylorboosh
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Registered: 3rd Apr 07
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I disagree with that last bit
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Rob E
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Registered: 1st Jan 06
Location: Madeley, Stafford....I want to live back in Wales!
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which bit?
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taylorboosh
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Registered: 3rd Apr 07
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just dont think thats what im on about..
i dont believe a bigger tip makes any differance..
the turbo sucking the air will make more differance than that
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