Exhaust Flow and Aero

[SPARKY]

SSS---IMO---this is a simple brain fart transposition ---shall we now call him Rick Perry  lol---he had the direction correct --just miss labled high goes to low ---- didn't mention the role of spill plates or end plates on wings to stop or curtail that flow ---YMMV---

[superford317]

Thank you sparky, you took the words out of my mouth, over 30 fully typed pages on Microsoft word and I get complaints about 2 words I get backwards in my haste. I try to proof read as much as I can, but I usually skip over the simple things and concentrate on the more complicated things. I hope slim will switch the 2 words around if not, oh well. Some of the posts are so long and I try to make them as understandable as possible so I repeat things as I see necessary to make certain areas more understandable to the less initiated or to new members that want to learn about such things.
Some of the things I am working on I do because there simply isn’t good sources on line, the NACA submerged inlet as example, I simply could not find good information on them, so I spent considerable time on the subject and I think a lot of people got a better understanding of them as a result and I have gotten several E mails thanking me for my work.
As the old saying goes you can’t please all of the people all of the time, but I do what I can.
If at any time there is a lot of clamor wanting me to stop I will be more than happy to do so.
As I complete 1 post I start 2 others and sometimes it gets a bit overwhelming trying to keep it all organized and straight.
Thank you and I am so sorry for the slip up I will do my best to make sure it doesn’t happen again.
IO thank you for your input.
We all make mistakes, to err is only human, such as SSS last post, thanking IB when we all knew he was refering to IO.
Sometimes I wish I could copy and paste or plagiarize someone else, it would keep me from making mistakes like this and save me a LOT of time, research and thought.
I enjoy doing this and helping to improve other peoples knowledge also and I am increasing my understanding as I delve into some of these subjects also.

[hotrod]

Actually there is excellent information on line regarding the NACA submerged inlet ducts.

The best place to go is directly to the source (ie NACA), NACA was responsible for the research that designed the ducts that now carry their name in the 1940's and early 1950's.All their technical reports are freely available on line. NASA currently runs a reports server that has all these reports but a few years ago they "improved" the online report system and it is now very difficult to find these old reports unless you know the magic search keys to find them. If you put in generic search keys in their report server you get literally hundreds of hits on common terms.

It is better to go the UK mirror for their reports that still have the old original report server structure where you can pull up reports by their year of publication and follow the development of research in chronological order. These reports also cover some very good research on engine design and detonation research and airfoil shapes during the war that is still very valuable information. Most of these reports were developed under the pressure of wartime research or during the early cold war jet development up to the Korean war, so they frequently came out with an initial report and a final report that are nearly identical, so you may find more than one report that contains essentially the same information. Some of them were also called technical notes and have TN numbers.

The easiest way to pull up these reports is to go to the UK mirror at:

http://naca.central.cranfield.ac.uk/

There you can pull up all the reports for a given year and thumb through them (this is good for days of very interesting reading) or if you have a clue what you are looking for use the search function to pull up reports that contain your search terms.

In the case of the NACA ducts, at the time they were doing the research they were called "submerged inlets" and "low drag inlets" Those search keys will pull up over 20 different reports about half of which cover inlets operating at low supersonic speeds and above, and the other reports at low to high subsonic speeds.

Best to read them in chronological order (year or publication is in the file name) for NACA ducts you can start with these reports.

http://naca.central.cranfield.ac.uk/reports/1945/naca-acr-5i20.pdf

http://naca.central.cranfield.ac.uk/reports/1948/naca-rm-a8i29.pdf

http://naca.central.cranfield.ac.uk/reports/1948/naca-rm-a8b16.pdf

http://naca.central.cranfield.ac.uk/reports/1948/naca-rm-a7i30.pdf

http://naca.central.cranfield.ac.uk/reports/1949/naca-rm-a9f16.pdf

http://naca.central.cranfield.ac.uk/reports/1950/naca-rm-a50e02.pdf

http://naca.central.cranfield.ac.uk/reports/1951/naca-tn-2323.pdf



Do not go to this web site unless you are willing to lose the better part of a month reading fascinating reports!!!

Larry

[SPARKY]

The "fix" is in   

[SPARKY]

WOW  thanks Larry!!

[WOODY@DDLLC]

Thank you sparky, you took the words out of my mouth, over 30 fully typed pages on Microsoft word and I get complaints about 2 words I get backwards in my haste. I try to proof read as much as I can, but I usually skip over the simple things and concentrate on the more complicated things. I hope slim will switch the 2 words around if not, oh well. Some of the posts are so long and I try to make them as understandable as possible so I repeat things as I see necessary to make certain areas more understandable to the less initiated or to new members that want to learn about such things.
Some of the things I am working on I do because there simply isn’t good sources on line, the NACA submerged inlet as example, I simply could not find good information on them, so I spent considerable time on the subject and I think a lot of people got a better understanding of them as a result and I have gotten several E mails thanking me for my work.
As the old saying goes you can’t please all of the people all of the time, but I do what I can.
If at any time there is a lot of clamor wanting me to stop I will be more than happy to do so.
As I complete 1 post I start 2 others and sometimes it gets a bit overwhelming trying to keep it all organized and straight.
Thank you and I am so sorry for the slip up I will do my best to make sure it doesn’t happen again.
IO thank you for your input.
We all make mistakes, to err is only human, such as SSS last post, thanking IB when we all knew he was refering to IO.
Sometimes I wish I could copy and paste or plagiarize someone else, it would keep me from making mistakes like this and save me a LOT of time, research and thought.
I enjoy doing this and helping to improve other peoples knowledge also and I am increasing my understanding as I delve into some of these subjects also.

Superford317 - sorry - it really wasn't a complaint just a comment. When we talk about complex phenomenon we can sometimes forget to reinforce the basics and then we tend to wander off topic like some of these threads! 

I have my own Superford317 file that I read and reread. This stuff is not easy to cogitate or verbalize! 

But to IO's point, some useful references or illustrations would help everyone.

To all  - keep it coming - these are some of the best forums on the net! 

[SPARKY]

Ahmen Brother PREACH ON!!  as the hung over Southern boy might say from the back bench on Sunday morning!!!!   

[Tman]

Me make pointy car, exhaust out back, drive fast.

[bobc]

"The mushroom cloud formed from a nuclear explosion is a vortice also. High flying jet aircraft leaving visible contrails is due to vortices."

Out of Superford's whole post, the first thing that caught my eye was this.  Dunno why. BS! I said, a mushroom cloud is just like a cumulus, a simple rising column of (extremely) hot air.  Visible high-altitude contrails are condensation from the exhaust, not the same as the teeny 'contrails' pictured in a previous post that occur under the right temperature and humidity conditions by vortex generators or simple high-to-low (I can understand the mixup there) flow at a wingtip.

Then I read the post (a good place to start, eh?).  And my fluid dynamics education is way too rusty to say yay or nay on some of it, but the aerodynamics as it relates to airplanes is spot on.  I'll give it a thumbs-up.

[superford317]

Amen brother “sparky”, I’m preaching to the congregation but that old devil rears his ugly head, aint that right brother “interested observer”
As hard as it is to believe, maybe I should have made my last post on vortices lengthier, so there would not be so much confusion, I could have explained more things in detail I suppose.
“bobc” you being from New Mexico you may be eligible for part of “the radiation compensation fund” since 1990 more than 1.4 billion dollars have been paid out to people that were exposed to radiation from government atomic bomb testing. The first atomic bomb ever detonated was named “the gadget” and the test site was named “trinity”. The location was near Alamogordo, New Mexico.
It was detonated 100 feet above the ground on a tower July 16 1945 at 5:29 mountain time and left a crater of glass 10 feet deep and over 1000 feet wide, the shock wave was felt over 100 miles away and the mushroom cloud reached 7 miles high. “The Gadget” only had an explosive yield of 20,000 tons of TNT, later you will see why I said “only” 20,000 tons.
The mushroom cloud is actually called a pyrocumulus cloud, “pyro” meaning explosion.
Mushroom clouds can be formed from any large explosion. I have witnessed them personally several times here in Iraq.
During the explosion a large mass of low density hot gas is created. The hot gas will rise very quickly.
The cap or crown of the mushroom, the round distinctive cloud on top of the stem, is caused by the rise and rapid expansion of the super-heated gasses forming vortices.
The entire cap or crown of the mushroom cloud is referred to as a vortex ring, if you are looking at the cloud, the right side is clockwise rotation and the left side is counter clockwise rotation. The massive vortices form a tremendous suction between them, drawing up dust, debris and smoke, that is what forms the stem of the mushroom, extending from the ground to between the counter rotating vortices.
Similar to the NACA duct, forming counter rotating vortices on its side walls, which greatly enhance airflow into the duct. The vortices draw in the airflow, down the diffuser ramp.
 Nuclear explosions are detonated above the ground to get the maximum effect from the shockwave and the fireball, if they were detonated at the ground surface like most conventional bombs, the ground would dissipate a large majority of the explosion.
Nuclear explosions in space or very high in the atmosphere where there is little air, would only have a round circular shape, No stem and no vortices or vortex ring.
The most powerful weapon ever tested by mankind was detonated by the Russians on October 30 1961.
The AN602 was a 3 stage hydrogen bomb nicknamed the “Tsar Bomba” its explosive yield was 50 megatons, equivalent to 50 million tons of TNT, 10 times the power of all conventional explosives used in WWII combined. Dropped from an airplane, it detonated 2.5 miles above the earth’s surface using barometric pressure sensors.
The fireball was seen 620 miles away. The mushroom cloud was 40 miles high and 25 miles wide. Brick buildings 34 miles away were totally destroyed and 3rd degree burns would have happened 62 miles away. A shockwave was seen in the air 430 miles away. The shockwave was still measured on seismographs on its 3rd passage around the earth. Windows were broken in Norway and Finland.
As built, the AN602 “Tsar Bomba” was designed to have double its as tested power, the test was at 50 megatons and it was built to be 100 megatons. Part of its Uranium 238 was replaced with lead to limit the power of the detonation, to limit the nuclear fallout. Lead is useful for other things than ballast and fishing sinkers I suppose.
It is unknown if any were ever built, but it was theorized and could have been built in the 1960s, known as the “Doomsday” bomb, A single large hydrogen bomb impregnated with cobalt, if detonated it would have killed every living thing on earth, unless you were buried deep underground and remained there for 5 years, essentially sterilizing the Earth from massive amounts of radiation.
Knowing the military and the intelligence of world leaders, what do you think, were they built?
An atomic bomb is very limited to the explosive yield it can be built to, where as a hydrogen bomb has no limit and can be built as powerful as desired, it takes an atomic bomb to trigger a hydrogen bomb. An atomic bomb is the splitting of atoms or “Fission” as in nuclear power plants and a hydrogen bomb is the combining of atoms or “Fusion” as powers the sun.
Our nuclear strategy was known as “MAD” mutually assured destruction. MAD indeed.
A major portion of the “Manhattan Project”, the development of the American atomic bomb in WWII, was carried out not far from my home, in Oak Ridge Tennessee.
Well, with the mushroom clouds and vortices taken care of, now on to jet contrails and vortices.
As was discussed in my last post on the vortices, the wing tip vortices can last for a considerable time behind the airplane.
The temperature and air pressure is reduced in the vortices and can cause moisture in the air to condense and cause the vortices to become visible.
Perhaps, in my post on vortices, I should have said, at certain times jet contrails at high altitude are visible, due to vortices.
I enjoy watching F1 races, that are ran in the rain and watching the vortices from the rear wing trailing behind the vehicles.
Now, back to the 6 other posts I am presently working on, in my meager spare time, for land racing. I think they will be very liked and informative to a LOT of people.

[SPARKY]

  how do you spell waiting with baited breath?

[Seldom Seen Slim]

I'll agree with Sparky, Mr. Ford.  While your essay is interesting -- it doesn't have much to do with land speed racing other than getting the subject from another post.  A few months ago we had quite a long thread going about a non-racing event - the tsunami and following issues with the nuclear generating station in Japan, and I let it go on since there was such widespread interest and many of our Forum members had cogent information to share.  But your post, being history, isn't all that pertinent to this Forum.  I'd therefore thank you to keep such posts short (if you elect to make any off-topic posts at all), and if you must go on at such length as you have (above) -- post a precis here and put the entire thing someplace where interested Forum members may find and read it.

Thanks, nonetheless, for the full story.  Too bad it isn't racing stuff. . .

[superford317]

Thank you for this wonderful site “SSS”.
When I attempted to keep the subject short and mention 2 examples in my post on vortices and aerodynamics I was called out, “BS”, so I attempted to give the full story so that it could be understood much better by our members.
I will try to refrain from quite so much detail in the future I suppose, if this has to be done again.
I need to get a portable scanner to use here in Iraq I suppose, I can include hand drawn pictures, one picture is worth a thousand words, as they say

[superford317]

Because the airflow patterns are so different between open wheel and closed wheel vehicles, this series of posts will deal with open wheel vehicles, specifically the air flow around the tires. Hopefully at a later date we can talk about airflow patterns around the tires on closed wheel vehicles.
A French inventor and engineer Nicolas Cugnot built the first known self-propelled mechanical vehicle in 1769. His creation was steam powered and made use of one of the first known methods to convert reciprocating motion to rotary motion.     
Viktor Schauberger from Austria was the first person to recognize vortices in nature.
Frederick Lanchester from Great Britain, made the first full descriptions of lift and drag and made models of vortices that occur behind wings.
Charles Goodyear invented the rubber vulcanization process in 1844.
Robert Thompson invented the pneumatic tire in 1846.
Tires with beaded edges were first used in the United States in 1892.
The Michelin brothers made the first pneumatic automobile tire in 1895.
Wheels for land speed racers have been everything from stock tires and rims to specific built race tires and rims to forged aluminum alloy rims with carbon fiber wound around them.
The thrust driven vehicles will usually have their tires and rims made of billet aluminum with carbon fiber wound around them, most rubber tires would disintegrate at the speeds these vehicles operate at.
Wheels and tires ran in open airflow will have very unstable airflow that moves from side to side as the tire rotates and will have large areas of airflow unsteadiness and separation. The turbulent airflow behind the tire is controlled by counter rotating vortices.
The tire sidewall profile, shape of the contact patch and if the wheel tire combination is running covers over the axle side and the outer side of the rim, will have a large influence on the airflow around the tire. The tire air pressure will influence the airflow around the tire also, as it will affect the shape of the tire and the contact patch. Wheel camber angle will affect the airflow and the vortices around the tire due to changing the tire deformation.
Most compressed air sources will contain moisture that will increase the expansion rate of the compressed air in the tires as they are heated. Dry nitrogen will expand at a lower rate than the moist air and hold the set tire pressure longer than the air. A drop of 25% in tire pressure will reduce the tire life by 15%. Nitrogen makes up 78% of the earth’s atmosphere by volume. Increasing the pressure in the tire will decrease rolling resistance and on hard surfaces will decrease stopping distance. Tires are permeable to air and will lose pressure over time. Severely overheated tires can give off flammable gasses and it can react with the oxygen in the air used to pressurize the tire and cause an explosion to occur, the use of nitrogen to pressurize the tire will stop this from happening.
Tires have a fixed shape and bad aerodynamics. The main function of a tire is to put the power to the ground and not aerodynamic properties. On an open wheel car the tires will typically account for 30% to 60% of the total drag on the vehicle and generate a large amount of unwanted lift also. The amount of lift the tire generates will depend on the size of the tire. The drag of the tire is proportional to the tire frontal area, so reducing the tire size will reduce the amount of lift and drag generated.  Tires and wheels on open wheel cars will generate more lift than drag. The tires can also greatly influence the airflow around the rest of the vehicle also, including the underbody and brake cooling as well as wings and upper body surfaces.
The atmospheric air pressure at sea level is 14.7PSI. Water vapor weighs less than dry air. Moist air has a lower density than dry air.  Drag and down force will increase as the air density increases. As air temperature increases air viscosity will increase also. As air density increases its viscous effects will increase.
Be sure the tires are spaced far enough away from the body, so the turbulence they produce will not interfere with the airflow along the body. By keeping the tires spaced at an adequate distance from the body, the air will have enough room to smoothly flow between the body and the tires, without the two air layers interfering with each other. If the two air layers were allowed to meet, the total drag generated would be greater than the sum of the two. The air turbulence from the tire, will usually cause the wake to spread out from 14in to 18in on each side, behind the tire, depending on the size of the tire and the speed. Because of interference from the axle-spindle side of the tire, the vortice and ensuing wake generated from the inner side of the tire will be less than the outside.
As the track width of the wheels is set wider it will give better stability but will affect spring rate and dampening. The narrower the track width of the wheels it will firm the suspension and the wider the track width it will soften the suspension.
Having the same track width for the tires, front and back, will aid in reducing drag. The front tire will break the air and the rear tire will pass through the hole the front tire made more easily, reducing the     drag on the rear tire. Like cars drafting or bicyclists following behind each other, the airflow is only disturbed once. In bicycle racing the rider produces 70% to 80% of the drag. A bicycle racer drafting the racer in front of him will exert 30% to 40% less energy. 
If it is a grooved tire running on a hard surface, there will be very little airflow passing between the tire grooves and the ground.
At high speeds, aerodynamics will affect the vehicle speed and acceleration rate more than any single factor in a LSR vehicle. The front surface of the tires is pushing against the air. The forward acceleration of the air generates drag. As the tire passes through the air it leaves a void behind the tire that that air moves into from all directions to fill. The air can’t move backwards through the tire and the air can’t move upwards through the ground. This results in forward drag and due to the forward and downward acceleration of the air in front of the tire, lift is generated because of a high pressure area at the base of the leading edge of the tire, just in front of the contact patch at the ground, as the surface of the tire moves toward the ground and the contact patch it moves energy to the stagnation point and increases the pressure as the speed increases.  Because of the tire rotation it will cause separation of the airflow at the top of the tire, earlier than would normally be expected. Due to the separation of the airflow at the top of the tire generating a low pressure area and the high pressure area at the base of the tire, lift will be increased more than normal. There will be a negative pressure at the backside of the tire, due to the void. At the rear of the tire, at ground level, the airflow will stagnate at the contact patch near the center of the tire and move to the left and right, splitting to each side of the tire. The airflow in front of the tire, then moves up the tire surface and towards the center of the tire due to the low pressure area located there. The high pressure at the front of the tire and the negative pressure at the rear of the tire will generate a pressure drag due to the differential pressure.
Because the tire is a circular shape, the air will treat the tire as if it were 2 different halves. The air hitting the front of the tire will move down from the center and the top half will move up from the center and over the top of the tire and separate from the tire surface. The air moving down from the center will strike the tire ground contact patch area and build up pressure.
Due to the rotation of the tire, the air flow in front of the tire goes down towards the ground and as a result, the stagnation point will be lowered closer to the ground and will continue to be lowered as the tire rotation speed increases.
Airflow around the tire and through the rim will depend on if the tire and rim combination are running wheel covers on the front and backside of the rim. Using wheel covers on both sides of the wheel, will reduce the drag by up to 25%. The wheel covers will stop the airflow from passing through the wheel from one side to the other and make the aerodynamics better around the tire also.
There will normally be 3 sets of vortices coming off of the tire, trailing in the wake behind the tire, they will be counter rotating.
 There will be a very small counter rotating vortice generated from each leading side of the contact patch and wrapping around the bottom of the tire and down each side, at ground level, following the shear layer into the wake behind the tire. The high pressure in front of the tire at the contact patch and the lower pressure at the sides and rear of the tire will cause the air to move laterally to the side of the tire and speed up, this is called “jetting”.
The second set of vortices are the largest and most persistent in the wake behind the tire. They will be generated at the center front of the tire, at the leading edge, where the airflow splits and travels down the front and up across the top. The vortices will wrap around each side of the tire. One vortice from the front center to the axle side and one from the front center to the outer side. Each vortice will be counter rotating, traveling from the center of the tire around the rear sidewall and into the wake behind the tire. The outer vortice will have a clockwise rotation and the inner vortice will have a counter clockwise rotation. The vortice on the outside of the tire will be larger and longer because it is in open airflow. The vortice on the inner side of the tire will be smaller in size and shorter in length because of the axle tube and the spindle affecting the airflow around the inner side of the tire.  These 2 vortices will dissipate slowly as they travel downstream in the wake, and will last for a considerable time. The Separation of the airflow at the leading edge of the tire causes an area of reverse airflow on the axle side and the outer side also. The separation will follow the curvature of the tire and will cover about 30% of the axle side and the outer side of the tire and rim surface. The airflow from the leading edge of the tire accelerates as it crosses over the face of the tire and moves toward the sidewall. Because of the airflow acceleration it will bypass the edge of the tire and create an area of reverse airflow with a weak velocity.
The third set of vortices will come off of the top of the tire, travel partially down the back of the tire before separating and traveling off into the wake behind the tire. The airflow forming the vortices off of the top of the tire will separate, because the air is slowing as it crosses the top of the tire and starts down the backside. These vortices will dissipate quickly, as they merge with the other vortices in the lower wake.
On a tire and rim with no wheel covers on either side, running on an open wheel vehicle, air will enter on the wheel axle side because of the closure of the airflow separation and circulate through the holes in the rim and then move downstream on the outside of the rim because of the low pressure area being generated in the wake on the trailing edge of the tire, creating a suction. Some of the air flowing from the outer, center of the rim, will partially go towards the area of reverse flow on the leading edge of the tire, but most of the airflow will go into the low pressure area behind the tire at the trailing edge.
Starting in 1991 air deflectors were used on F1 cars to blow air into the low pressure area behind the front tires, to lower the drag generated by the tires. In F1 the open tires generate 50% of the drag for the entire vehicle. A good example to look at, for the front air deflectors, would be the 1993 McLaren MP4/8 F1 car.
Because of the rotation of the tires, the vortices they generate and the pressure differentials created, the tires can have a large influence on airflow around and underneath the vehicle if they are not kept at a distance from the vehicle body.
The tires generating a wake at their backside, creates a negative pressure, which can pull airflow from under the vehicle. This can lower down force, if the vehicle was set up to generate down force from the underbody.
The tires generate so much drag it would be worthwhile to add some air deflecting devices to channel some airflow into the wake behind them, to reduce the negative pressure and reduce the drag being generated. Some engine exhaust, if rules permit, can be redirected into the wake behind the rear tires to lower the size of their void. The air deflectors will add some drag but at a cost of having a lower overall drag due to the tire drag being decreased.

[SPARKY]

Is the greater gain above or below the rear axle?? Inquiring minds need to know? 
well at least a go faster want-a-B