Increase Flow Speed: Improve Efficiency with Vortex Generators or Shark Skin

[Becks]

Hey I am attempting to increase the flow speed of fluids (air, water, what have you) through a tube for a project, in an attempt to make the flow faster and more efficent. I've debated using vortex generators inside the tube, or perhaps a surface resembling shark skin. If anyone has any imput here I would greatly appreciate it.

 

[Pyrrhus]

Well the continuity equation for "dry water" (ideal fluids) says:

$$Av = Constant$$ where A is transversal area and v is speed, so the smaller the area the faster the fluid speed.

 

[Becks]

yes, but I need to keep the tube at roughly 2.5 inches, so how would I cause air to flow faster through the constant sized tube? Note the air will start at an unvariable speed.

 

[Clausius2]

yes, but I need to keep the tube at roughly 2.5 inches, so how would I cause air to flow faster through the constant sized tube? Note the air will start at an unvariable speed.

Heating the tube. Adding energy in heat form you will increase the flow speed.

PD: It has a limit, but surely you are at #Mach<<1 and therefore it doesn't matter.

 

[Becks]

The air traveling through the tube is already heated and cannot be changed. Basicly this for a project on how to increase the speed of a car exhaust's system by changing the interior surface of the tubing.

 

[enigma]

Are you able to put a 'shute' in front of the section of pipe? A funnel out in front of your test section would increase the velocity.

 

[Becks]

Could you explain how the shute would work? The exhaust header feeds directly into the exhaust pipes, so would it go right at the header? Also, would changing the surface of the pipes do anything? Vortex Generators? Tubercles? shark skin texture?

 

[enigma]

Oh sorry. your post on the application wasn't up when I posted my part

 

[Astronuc]

What is the basis of vortex generators. It would seem that a passive vortex generator would use some of the flows axial momentum to generate the vortex and thus impede the axial flow.

On the other hand, rifling the bore without decreasing the cross sectional area.

See "laminar flow around a golf ball !" at http://www.allstar.fiu.edu/aerojava/faq_princ_flight2.htm
(you'll have to use Edit/Find with the browser on that page)

"Dimpling like a the surface of a gold ball might help. But golf ball surfaces have been optimized and I don't know if that effect has been applied to closed channels.The golf balls without dimples would have a higher drag coefficient as seen in many pictures found in Schlichting's book on Boundary Layer Theory. However, dimples are placed to trip the flow from laminar to turbulent and keeping it attached for a longer distance along the golf balls' surface, . . ."

 

[Cliff_J]

Becks - I would assume you're talking about doing things beyond the typical use mandrel bends instead of crinkle bends, minimizing the number of bends, ceramic coatings and so on that are existing means of maximizing flow.

If you're trying to simply optimize flow that is one thing, but if you are trying to optimize flow over a certain range of operation that is another. The exhaust gases are pulsed so its more like an AC current with a large DC offset to use an electrical analogy. So like on the induction side where intake tract and plenum dimensions are factors, you may be able to take advantage of this and create another version of the "Tri-Y" headers used on cars or the 4-2-1 motorcycle headers.

There is research out there on just the benefits of having a "H" or "X" pipe in the exhaust for a true dual exhaust and the predominant theory has to do with an effective reduction in the impedance presented to the pulses. No idea on the validity of the theory and if any data was collected or if it was speculation, but might be something you could take advantage of as well.

Cliff

 

[LunchBox]

Basically, what the problem comes down to is viscosity.

You're trying to minimize the surface effects of the fluid along the interior surfaces of the pipe.

Since viscosity is the product of shear stress at the wall surface and the gradient of the axial velocity at the wall, that's your answer...

You need to minimize both the shear stress and the velocity gradient. Do some quick research and see how both of these can be minimized.

Hope that helps...