Port flow between floor and roof?

Post by **ou812** » Thu Feb 10, 2005 11:27 pm

Hi all...got a question for ya. When probing a port and finding that the velocity is high on the floor near the short turn, and then probing the roof around the short turn and back towards the valve and finding the velocity is low...alot lower than the floor, does this always mean that the roof is flowing the majority of the air because of the velocity below it or just the opposite?
Brian

Darin Morgan · Post by **Darin Morgan** » Fri Feb 11, 2005 9:40 am

ou812 wrote:Hi all...got a question for ya. When probing a port and finding that the velocity is high on the floor near the short turn, and then probing the roof around the short turn and back towards the valve and finding the velocity is low...alot lower than the floor, does this always mean that the roof is flowing the majority of the air because of the velocity below it or just the opposite?
Brian

Your question is not easy to answer in a simple paragraph. You need to study up on the, "Coanda effect" the "Bernoulli principle" and boundary layer conditions as they exist in sub sonic air flow through a pipe or around bends in ducting. The web pages below should point you in the right direction and shed some light on your questions. If you really concentrate on the Bernoulli principle and the related variables of, Pressure, volume and velocity and how they are intertwined and dependent on one another, the stuff you see on the flow bench makes a lot more since. The Coanda effect explains why the airflow wants to adhere to even a sharp SSR at lower velocities and why it breaks the boundary layer at higher ( critical ) velocities. The critical velocity depends on the design your dealing with, the air speeds and the size of the ducting or port.

http://home.earthlink.net/~mmc1919/venturi.html

http://theory.uwinnipeg.ca/mod_tech/node68.html

http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html

http://www.aardvark.co.nz/pjet/coanda.shtml

http://encyclozine.com/Coanda_effect

.

Post by **ou812** » Mon Feb 14, 2005 12:11 am

Thanks very much Darin. Stopped by the reher/morrison pits on Sat. in Pomona, but didnt stay long. Was curious about your new found information with wet flowing heads and why it has not helped you guys...seems your qualifying about the same. Dont take that as mean or bad...not trying to do that at all!!!! Just wondering whats up with the new tech?
Thanks again Darin!
Brian

cboggs · Post by **cboggs** » Mon Feb 14, 2005 12:51 am

Darin,

Care to expand on this a little, .. the described head flow, ..

I have a "reasonable" understanding but I'd like to hear your take on it.

Cheers.

Curtis

Post by **ou812** » Sat Feb 19, 2005 12:45 pm

Bos's5.0 · Post by **Bos's5.0** » Sat Feb 19, 2005 1:28 pm

I would like an answer as well. I have found the exact same thing on my E7's I just probed.
If this is the common case, what are the common porting steps to
A. slow down the SSR so it don't choke so fast.
B. slow down the very high velocity cylinder wall side of the port.
C. Possibly Balance out the flow across the Port, if this is even possible or desirable.

Post by **ou812** » Mon Feb 21, 2005 9:23 pm

todd8541 · Post by **todd8541** » Mon Mar 07, 2005 11:27 am

There are some things missing in those links that doesn't explain what is happenly entirely as it relates to your findings from the probes.

On the link that has the converging and diverging link it shows the air in the throat section of the venturi (the smallest crosssectional area) being uniform throughout the crossectional area. This is false in real life. In real life the velocity closest to the walls will be higher than the middle. This is because all of the air trying to compress into the small section doesn't compress uniformily accross the section.

First break down the venturi into two sections. One being the throat area extended to the entrance of the nozzle. The second being the area or volume outside of the throat area to the entrance of the nozzle (think of coring an apple. the core is the first section and the outside being the second. What happens is all the air in the second section is trying to force it's way into the first section. The inside air doesn't compress as much as the outside therefore requiring the region at the walls to increase it's velocity because it is trying to flow more air than the middle section.

Just because a crosssectional area round doesn't mean the flow is equal all the way accross the crossectional area. If your short turn radius has a ramp leading to it that is why you have this situation.

Then the because of the coanda effect the air bends with the radius and stays attached to the wall.

I hope this helps if not i will try to think of a better way to explain it.

Todd

Grocerius Maximus · Post by **Grocerius Maximus** » Tue Mar 08, 2005 3:19 am

Y'all might find this stuff interesting, they debunk common theories in aerodynamics and claim Bernoulli Principle to be completely false.

http://www.aeronautics.ws/blunders.html

OldSStroker · Post by **OldSStroker** » Tue Mar 08, 2005 8:33 am

Grocerius Maximus wrote:Y'all might find this stuff interesting, they debunk common theories in aerodynamics and claim Bernoulli Principle to be completely false.

http://www.aeronautics.ws/blunders.html

I only got thru part of it, but I especially liked the part about Burt Rutan and the Voyager: " Burt Rutan had the wings of the Voyager on backwards and upside down! " Damn, just think if they had been mounted "correctly" how much easier it would have been for Dick and Jeana.

It all reminds me of the "bumblebee flight theory": A bunch of aerodynamisists, perhaps Clifton Gene Gent among them, studied the bumblebee and decided that, according to their interpretation of physical principles governing flight, it was impossible for a bumblebee to fly. Fortunately, they neglected to tell the bees, so they just kept flying as they had for many generations.

todd8541 · Post by **todd8541** » Tue Mar 08, 2005 8:57 am

A quotation from this page

http://www.aeronautics.ws/blunder5.html

"Engineering says:

1. Air is incompressible."

When did they change that theory.

Todd

Grocerius Maximus · Post by **Grocerius Maximus** » Tue Mar 08, 2005 9:51 am

I was mostly referring to the section on venturi effect and how they believe it actually works, and the sections describing the wing tests with holes thru the skin to measure pressures, and how he (they) believe you aren't actually measuring pressure, but siphon pressure. Then trying to prove that theory by putting a wing pivoted on the CG and the wing at 0 AOA and having it rotate DOWN when all the 'pressure' test data gathered over the decades says it shouldn't. There are some interesting things in there that may affect how one thinks on ports. New thinking might just lead to new performance.

bc · Post by bc » Tue Mar 08, 2005 11:17 am

Someone should try building a carb. like that to see how well it works.

todd8541 · Post by **todd8541** » Tue Mar 08, 2005 3:34 pm

I will try to print some of it off tonight and read thru it.

Todd

todd8541 · Post by **todd8541** » Wed Mar 09, 2005 7:59 am

I printed the web page out yesterday and read as much as I could before I had to get some sleep. While there are some information I would agree with there are some inconsistancies that make me leary on other points. I left him a message because there are some questions I have. I hope he calls as this is some interesting stuff the more I read into it.

Todd

Don Terrill’s Speed-Talk

Port flow between floor and roof?

Port flow between floor and roof?

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