Talk:Velocity stack

Motorhead, why would you be so disrespectful and completely whip out hours of work that was put into the updating of this article. I felt I respected everyones content by leaving it present either verbatim or reworded. You completely whipped out all my work, including legitimate references that give this article substance and external references to clarify and allow further research. The original content was good but left many dead ends, such as where you get the flow coefficents from, "dynamic tuning range", "reverse megaphone", "dynamic tuning speed". --BryanPendleton (talk) 18:48, 27 October 2009 (UTC)[reply]

Thats EXACTLY what you did to my work. Not to mention that, regardless of your references, your additions are rife with errors. My flow coefficents are correct and yours are wrong. See below. . .

Head loss coeffients are not the same as Flow Coefficients. I sited references. Do you have references for your Flow Coefficients? Please post your numbers if you have some references and the context of what the Flow Coefficients are. --BryanPendleton (talk) 15:27, 30 October 2009 (UTC)[reply]

"By altering the curvature and radii of the velocity stack allows for small changes in the velocity profile of the air flow into the induction system, thereby allowing an engine to be tuned to increase the engine's volumetric efficiency at a given engine speed"

... is pure bunk as anyone spending any time at all on a flow bench or dyno will tell you. In fact all that is required to get an accurate flow test is a crudely shaped radius of clay. If what you said was true then almost all the flow tests ever done were out to lunch.

Flow bench test and fluid velocities are two different things. A flow bench test provide flow rate data.. It does not tell you the air velocites as it enters the combustion chamber, and how that influences the combustion process. Are you claiming that inlet geometry does not effect the development of the air velocities? I have run numberous CFD analysis's and have studied enough Fluids to understand the impact of geometry on internal viscous flow. I have flow bench tested different velocity stack profiles to back up CFD work.--BryanPendleton (talk) 15:27, 30 October 2009 (UTC)[reply]

"The acceleration of air flow into an engine's induction system is an area for appreciable head loss, or the loss in mechanical energy driving the air flow. The differences between a sharp cornered inlet and a radiused inlet can be significant, particularly if separation of the boundary layer occurs due to poor inlet geometry." ...Again incorrect. What I wrote was correct, not this. There is very little to be gained by playing with the radius beyond just making it smooth. Just try it on a flow bench. It is the LENGTH of the stack far more than the radius that affects engine behavior.

You are arguing engine performance impact, in which I agree. The impact of the induction system inlet is minimal in the grand scheme of the things, but from a flow stand point the inlet geometry can have a heavily impact flow capacity. As sited in by Introduction to Fluid Mechanics ^[1] --BryanPendleton (talk) 15:27, 30 October 2009 (UTC)[reply]

" The head loss coefficient of a well-designed velocity stack or inlet appproaches 0, meaning the head loss at the inlet is near 0. In comparison a square-edge inlet will have a head loss coefficient on the order of 0.5. For reentrant flow inlet the head loss coefficient increases to over 0.7." ...A square edge ORIFICE PLATE will have a .61 coefficient. The coefficient of a plane ended pipe is .9 and of any kind of radius .98-.99.Where could you find 0.5 in a velocity stack? what you decribe is not only incorrect it bears no relation to anything in a velocity stack. Head loss coefficients are different from Flow Coefficients. My head loss coefficients were substantiated by Introduction to Fluid Mechanics ^[2] --BryanPendleton (talk) 15:27, 30 October 2009 (UTC)[reply]

"The air velocity at the wall of your induction system or intake will always be 0 due to the viscous drag." ... it is NOT due to viscous drag it is due to WETTING. It is Velocity PROFILE developement that is due to viscous drag. Wetting is simply a term for the surface area in contact with the fluid, it does not "cause" anything. The fluid velocity relative to the suface is zero due the viscous effects, resulting in a "no-slip" condition, viscous drag. Sited in Fluid Mechanics .^[3] --BryanPendleton (talk) 15:27, 30 October 2009 (UTC)[reply]

"Comparing these coefficients for inlet geometry, there is a significant impact on the flow rates possible at the inlet of your engines induction system." ... Since your figures bear no relation to induction systems this is not true. Huh? Induction systems must have an inlet. . . that makes it relevant.--BryanPendleton (talk) 15:27, 30 October 2009 (UTC)[reply]

"As the air enters the induction system, the boundary layer thickness will be large causing the air velocity at the center to be at or near its peak, assuming a constant cross-section area. As the air travel downstream the boundary layer grows smaller, as does the peak velocity at the center of the induction system.[2] The development of this velocity profile and the peak air velocities as the air enters the combustion chamber is what allows the engine's volumetric efficiency to be tuned. The velocity stack allows a tuner to alter the development stage of the velocity profile and the air velocities as the air enters the combustion chambers, all of which can aid improved fuel combustion and volumetric efficiency" ...The velocity profile only becomes fully developed many diameters down stream. The entry has a largely uniform velocity distribution except and the very edge near the wall. Only later does the drag from the wall reach all the way to the middle.

You are absolutelely correct about the velocity profile becoming fully developed and it is unlikely that the profile will become fully developed. Nor with the flow rates would the viscous effects every reach the middle. I was mistaken in my explanation of the boundary layer development mechanics, thats what i get for multitasking. I will make the necessary corrections.--BryanPendleton (talk) 15:58, 30 October 2009 (UTC)[reply]

I wrote this article to combat myths such as those you put forth. You took it upon yourself to change the meaning from what was correct. Any book on fluid dynamics will bear all this out. Including, Im betting, your own references. Additions are welcome so are bonafide corrections. But this is defacement.--=Motorhead (talk) 23:16, 27 October 2009 (UTC)[reply]

I am human, I do make mistakes and I am not afraid to admit it, but short of my mistake on the boundary layer development, everything else if sustantiated by my references. Please point us toward your references and I am sure we can compile our knowledge to best educate the enthusiasts out there. --BryanPendleton (talk) 15:27, 30 October 2009 (UTC)[reply]

Everything I put forth was from fluid dynamics books and I put up references. I would like to work with you if possible to put together a professional article that will address both the application, basics for the laymen and the hardcore mechanics. Please let me know if you are willing to work together?--BryanPendleton (talk) 15:27, 30 October 2009 (UTC)[reply]

I have "introduction to fluid mechanics" sixth edition fox mcdonald pritchard. what pages/chapters are you referring to? p341-343 discusses minor loss coefficients. I see very little that can apply to velocity stacks other than to say (p343) that beyond r/D >0.15 "K" will be 0.04. Which is to say that a 2inch pipe with any radius greater than .3" will have a minor loss coefficient of .04 which is vanishingly small when considered it is the large end of a full intake system whose major loss by far occurs around the valve seat and at the turn. There are much more focused and appropriate references than this book which seems to be geared to introductory industrial pipeline theory. I am digging up better references for this and other articles but as far as this article is concerned there is little more to add which can be usefull to general readers. Bottom line is still that once you have your lengths and volume/diameters in order, there is little/nothing to be gained by spending time on the exact details of the stack radius shape. But if you can show different by all means show me. Keep in mind that this topic in this context is far more exacting and advanced than general fluid dynamic texts will address.--=Motorhead (talk) 00:03, 31 October 2009 (UTC)[reply]

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"Plane pipe" ...I think you meant "Plain pipe", no?--Hooperbloob 00:27, 24 October 2006 (UTC)[reply]

Quite right THANKS!--=Motorhead 01:55, 24 October 2006 (UTC)[reply]

How could velocity be improved on a stack? Would a cone at the centre..similar to a ramjet improve it?

No it is already so efficient that anything else might hurt it. The point is not velocity at all, it is smooth even flow into the pipe.Flow in supersonic systems is nothing like flow below the speed of sound. Ramjets run under completely different conditions.--=Motorhead 01:22, 29 November 2006 (UTC)[reply]

2 "Slightly modify... duration of pulses within the tract." doesn't sound right, is probably poorly worded for your intention. If it is correct, please offer references. Tim S. 10/19/07

It is correct. If you take the entire sentence, it explains how the shape of the bell resembles a reverse megaphone thereby extending any wave passing throught it in either direction, however because it is short its effect will be slight but noticible.--=Motorhead 13:47, 21 October 2007 (UTC)[reply]

Effect on aerodynamics[edit]

It's not clear from the article whether velocity stacks in cars normally go through the hood, as seen in supposed 'custom cars'. If so, does the reduction performance due to the loss of aerodynamic efficiency offset the gain from the increased engine breathing efficiency? Centrepull (talk) 06:03, 27 October 2009 (UTC)[reply]

That was done routinely years ago. It was better to have the power gain which more than offset the aerodynamic drag. Back then though it was not appreciated how much loss that drag could cause. You can have your power without the loss now. All intake pipeing is directed to a scoop of some kind now which has much less drag. Check out the hood scoops on modern pro stock cars or any F1 car.--=Motorhead (talk) 21:36, 28 October 2009 (UTC)[reply]

References[edit]

^ Fox, Robert W. (1973). Introduction to Fluid Mechanics. John Wiley & Sons, Inc. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Fox, Robert W. (1973). Introduction to Fluid Mechanics. John Wiley & Sons, Inc. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Potter, Merle C. (1982). Fluid Mechanics. Great Lakes Press, Inc. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

This article is extremely poorly written[edit]

Just from an editing standpoint this article is terrible. There is no direction to it at all; It's just a whole bunch of random facts thrown on to a page. Sentences are strangely worded and don't make sense. Also the lack of references is disturbing. —Preceding unsigned comment added by 68.49.32.156 (talk) 21:36, 4 December 2010 (UTC)[reply]

[1] Fox, Robert W. (1973). Introduction to Fluid Mechanics. John Wiley & Sons, Inc. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

[2] Fox, Robert W. (1973). Introduction to Fluid Mechanics. John Wiley & Sons, Inc. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

[3] Potter, Merle C. (1982). Fluid Mechanics. Great Lakes Press, Inc. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

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