Landracing Forum
Tech Information => Aerodynamics => Topic started by: Seldom Seen Slim on May 26, 2011, 08:33:20 PM
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It's been suggested that this forum might benefit from having a free and self-standing aerodynamics topic. That is -- all of the aero questions and comments and ideas would be here (well, in an ideal world, but that's another story). Having aero as a topic would make it easier for someone that's searching for something particular in aerodynamics as it relates to land speed racing -- would need only to click on the topic and scan through the various threads. As it now stands a viewer must work his way through a zillion posts and the search engine feature. We've got topics for EFI and steering and water/methanol - it isn't difficult to add another one.
Unless I hear a groundswell of dissent -- I'll start one tomorrow or Saturday.
You're welcome, RX.
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Fire it up! I need some help.
Bob
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Thanks Jon
First I read a book about aerodynamics then studied all I could find on the internet. After that I took an aspirin for my head and removed all my fairings .I will run Modified from now on .
These are some of my questions.
should the point be at the front ?
should the point be at the back?
what are Reinolds numbers?
What is laminar flow?
why doesn't everyone have golf ball like dents in the fairings?
what about the sides?
What is wrong with covering the front wheel?
how much effect does rider movement have on the coefficient of drag?
how dose a wind tunnel work? dose moving the air at 85 mph then doing math really get the same results on vehicles ment to go 300 mph?
Why does a 50 caliper bullet have a blunt tail end ?
is a tear drop a good aerodynamic shape?
dose paint surface texture make any difference?
dose air temperature make any difference?
even if one of these questions gets answered it would lead to ten more.
See . That is why I just run Modified. :-D
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That would be a good topic.
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Great idea Jon. Experience has shown me that we usually think we know a lot more about this subject than we actually do.
Pete
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See, it wasn't that difficult to set up, was it, Slim?
Okay, boys and girls, you've got a new board/topic available to you. Use it for darn near anything about aerodynamics. Post your ideas, your questions, your tall tales - whatever, it's all about the movement of your vehicle through the air - and of the air moving around your vehicle.
I've pointed out to Dave Salazar (A2 Wind Tunnel) that the board has been set up. I did not make him the official "go-to" guy - on purpose. If he checks it now and then (just like everyone else will probably do) and decides to comment or ask or answer -- that's his choice. You're welcome to ask him a question via your post -- but if he doesn't respond it's his choice. He is not a moderator and isn't the designated answer guy. Ditto with others that we know are strong in their knowledge and application of things aero-related. This is an open subject. Use and enjoy and learn, hey?
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Yes, great idea.
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:cheers:
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Please observe small red car in picture to the left. What's this about Aerodynamics?
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What a good idea Slim,
Here's my question, I , like most, enjoy learning as much as possible about aero, and have looked at many wind tunnel videos , both cars and bikes, but I have never seen, or do I understand how the air flows past the front wheel (bike) and what effect this has on the air flow behind it.
How much travels over the top of the fender and between the fork legs on a naked bike ?, same question applies with APS bikes.
I realise the plan is to split , and try and control the flow with APS bodywork, but have always wondered what benifits can be obtained from the fenders in the various bike classes, as opposed to no fender at all ?
Tiny :cheers:
(edit,,oops,,,posted soo close to the right spot)
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Please observe small red car in picture to the left. What's this about Aerodynamics?
Rich, but you have enough HP to push the little Red Brick through the air !!!!
Cool car, but then again I am biased,, I like the old classic and vintage stuff.
Charles
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I think I've fixed things now. I managed to get two (count 'em, TWO) aero topics set up. So I just now merged them into one. You shouldn't have to read sorta-double any more.
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Thanks for the sub-forum!
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A well designed front fender can efficiently split the airflow and help it pass alongside the fairing. Also, the fender contains the turbulent airflow around the upper half of the spinning front wheel. Both of these features help reduce aero drag.
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A well designed front fender can efficiently split the airflow and help it pass alongside the fairing. Also, the fender contains the turbulent airflow around the upper half of the spinning front wheel. Both of these features help reduce aero drag.
Silly wallrus, Real racecars don't have fenders! :evil: :cheers: :-D
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You've got to remember the reason he's wobbly is because he only uses two wheels! :evil: :evil: :evil:
Pete
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Dose any one have a Video of a normal street type motorcycle in a wind tunnel with the wheels spinning? And a smoke trail. I think that would be fun to see.
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John, thanks for the new sub forum. :-)
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Please observe small red car in picture to the left. What's this about Aerodynamics?
Which red car?
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Thanks Jon
First I read a book about aerodynamics then studied all I could find on the internet. After that I took an aspirin for my head and removed all my fairings .I will run Modified from now on .
These are some of my questions.
I'll give it a shot I just hope Blue doesn't tear me up too bad but I will not mention frontal area!
should the point be at the front ?
"It doesn't much matter how you open the hole, it is all about how you close the hole."
Pork Pie Wendover KOA August '06 (Thanks Sparky!) Except for the Bloodhound SSC!
should the point be at the back?
"It doesn't much matter how you open the hole, it is all about how you close the hole."
Pork Pie Wendover KOA August '06 (Thanks Sparky!)
what are Reynolds numbers?
Osborne Reynolds discovered the parameters that mathematically attempt to describe the changes from laminar to turbulent flows. (Ratio of inertial and viscous [friction] forces.) If you build a 1/4 scale model for a wind tunnel then the speed has to increase by 4X to keep the Reynolds numbers the same. (Similarity Parameters?) Then a 400 mph test has to be at 1600 mph and the air behaves (compresses) quite differently. Now what if we increase the pressure in the wind tunnel?
What is laminar flow?
Classic example is cigarette smoke wisping from the end starts as laminar (parallel layers) and changes to turbulent. Laminar is how everyone (thinks or) would like the "fluid" to go. If we could get the flow in pipes to stay laminar at higher Reynolds numbers it would save huge amounts of energy in pumping fluids. Likewise our taters could go faster with less HP!
why doesn't everyone have golf ball like dents in the fairings?
Because they don't want to spin like a golf ball? Or they do not live in a active, large hailstone area?
what about the sides?
See above!
What is wrong with covering the front wheel?
What if the front fender really acts like a scoop?
how much effect does rider movement have on the coefficient of drag?
If you change your shape (i.e. bigger butt (I DID NOT SAY FRONTAL AREA!)) or change the closing of the air (length & position of big butt) you change the actual shape of the airflow (which never matches the vehicle BTW) and hence the Cd! The Cd is really just for comparing different aero(?) shapes. Refer to Pork Pie quote again!
how does a wind tunnel work? does moving the air at 85 mph then doing math really get the same results on vehicles ment to go 300 mph? Maybe not perzactly, but near enough or so the wind tunnel guys claim!
Why does a 50 caliper bullet have a blunt tail end ?
It's a supersonic thing and it works for 7.62 also! The X-1 was shaped like a 50 cal cause that was considered good at the time and it worked out for Chuck Yeager!
is a tear drop a good aerodynamic shape?
Works great for tears and rain drops!
does paint surface texture make any difference?
Just depends on the texture, boundary layer and Ozzy's numbers. (Google shark skin & riblets!)
does air temperature make any difference?
Temperature changes the air density - all other things equal you can go faster in thinner air.
Wonder if submarines can go faster in lacquer thinner?
even if one of these questions gets answered it would lead to ten more.
Sorry, I couldn't get to ten!
See . That is why I just run Modified. grin.
Buy more aspirin this Subaru never ends! Or make the fairing lots longer like certain green, blue & red machines! And remember this: “... as Sir Cyril Hinshelwood has observed ... fluid dynamicists were divided into hydraulic engineers who observed things that could not be explained and mathematicians who explained things that could not be observed.” - James Lighthill
BTW Rich, even a little red brick sitting on top of a larger red brick with wheels can be improved some!
Enzo Ferrari once said the aerodynamics was for those who can't build engines! But when the HP$$$ run-out then what?
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My day job is a hydraulics engineer and salesmen show me new things they develop or invent. A fellow showed me a velocity stack for a culvert entrance last Friday. He claims this improved inlet will make the culvert flow more water.
Note the enlarged throat just downstream where the inlet converges. Has anyone seen this before? Will it improve air flow, specifically, to enhance the performance of a velocity stack on a carb inlet?
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I am just a hotrodder, make it small in front and apply the loud pedal! :-D :cheers:
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My day job is a hydraulics engineer and salesmen show me new things they develop or invent. A fellow showed me a velocity stack for a culvert entrance last Friday. He claims this improved inlet will make the culvert flow more water.
Note the enlarged throat just downstream where the inlet converges. Has anyone seen this before? Will it improve air flow, specifically, to enhance the performance of a velocity stack on a carb inlet?
Take a look at the Ratech inlet restrictors used on almost all road race cars these days.
There is a good picture of the cut away and the pressure wave somewhere on the site.
These are used to equalize the motors and work very well.
John
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WOW thanks Woody that answers my questions .I still am confused as all get out but it dose answer some.
So the little dents in a golf ball are to help the ball move straight while spinning? That makes sense.
My question about the wind tunnel comes from Craig Breedloves Spirit of America. The large rear fin was meant to keep the car straight. At some point the pressure on the verticle fin lifted the front wheel off the salt. Is that something that a wind tunnel would find? Or is that where the fun is.
I know that a tear drop is a fake shape. IE a drop of liquid will form a ball. Like in a shot tower. But should I make a fairing like a tear drop or like an egg or like a ball?
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like a fish tail :-P :?
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I have that allready . It just needs to be wider to fair in my legs. I guess the next question is . Fo a tail sectionwould a verticle blade or a point be better?
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Racer x, Is the bike a mps or aps?
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I only run my bike in Modified.OR Modified Partial streamline. If I go altered then I can run any engine and any frame and do all sorts of thing with fairings.I would go broke fast with that many options, :-P
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Dose the turbulent boundary layer remain intact because the ball is spinning? or because the ball is dented? I mean would a ball with dimples held still in a wind tunnel have a lower CD than a spinning ball with dimples ?
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I don't have info on that particular test criteria, but suspect it was not spinning. As the dimples are turbulators, creating turbulance in the boundary layer. Laminar flow has less drag, but it is more prone to separation and drag rises because of eddies that form in the gap. Turbulent flow has more drag initially but also better adhesion, and therefore is less prone to separation. If the shape of an object is such that separation occurs easily, it may be better to turbulate the boundary layer at the slight cost of increased drag.
On the premiss that a shark "glides" 20 percent faster than most other fish, we worked on sharkskin for awhile. 1st problem being it tests best in a water tunnel. 2nd problem being we received an email within the last month from a researcher who filed a provisional patent on the geometry of sharkskin giving us a heads up to discourage further investigation. Seems the future use is to cut fuel consumption on ships, but there is some work being done in imitation sharkskin in Germany; the technical hurdle is how to apply it and will it keep organisms from fouling the surface. Dried sharkskin makes a better sandpaper than drag reducing medium.
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Racer X, a modified frame is a good idea for a person who is serious about aero. The chassis needs to have all wide parts at about the same height. In other words, the wide part of the fairing ahead of the head, shoulders, and hands should be about the same height as the broadest section of the tail behind one's boodie. Also, the wheelbase should have ample distance to allow streamlining with a non-truncated teardrop shape. None of the standard street bike chassis I have seen provide this.
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That is my next BIG modification. I need to extend the rear wheel so I can make a better rear fairing . and still Keep it 3 inch behind the tire. As it is now I am sitting on the rear tire. The extended swing arm will allow me to hide the nitrous bottle in front of the tire keeping out of the slipstream.
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Please observe small red car in picture to the left. What's this about Aerodynamics?
Which red car?
This red car
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How would you describe that color? -- Brick red?
Stan
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I don't think that it's "resale red" :mrgreen:
Mike
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There are some really good aero books out there. My favorite is:
Fluid Dynamic Drag by Hoerner 1965...This guy did a lot of aero work designing the Me109 for the otherside and after the war for Lockheed. The book is full of wind tunnel data all explained with equations...you can ignore the math and with reasoning learn from the graphs ....the car stuff is really old but informative...The section on interference drag is priceless. I feel that interference drag is the dirty little secret that modern CFD and fancy computer programs don't handle well. The section on transonic speeds should quiet fools that think 1000 mph with a tire driven car is possable...(as long as tire driven is traction and not salt shredding pikes or something).
I have other books I like. Please add to my book review or describe your source of wisdom?
Akk
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off to Amazon :cheers:
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Shape and Flow. The fluid dynamics of drag by Ascher H Shapero..
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The red car to the left has the aerodynamics of a bale of hay but who cares it's kool :-D. What is it that guy says "given enough velocity even pigs can fly"
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Here is an image of the NAE and the pressure against the wheels and the shock wave generated at locations around the fuselage.
This is using Ensight and CFD++ software. This is of course with no fairings installed at this time.
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I have a foto of Thrust breaking the sound barrier from above, the dust cloud [shock wave] goes straight out at right anglels from the sides from front of streamliner for a great distance.
Do any of the CFD programs show the same results?
JL222
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CFD shows the whole cone formed by the shock wave or at the surface.
(Pix from Thrust & Bloodhound sites.)
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There are some really good aero books out there. My favorite is:
Fluid Dynamic Drag by Hoerner 1965...This guy did a lot of aero work designing the Me109 for the otherside and after the war for Lockheed.
I have other books I like. Please add to my book review or describe your source of wisdom?
First published in 1951 and updated in 1965, it has never been superseded.
Best book on aircraft design: "Aircraft Design: a Conceptual Approach", Dan Raymer. Lots of tables, illustrations, and examples so you don't get lost in the math.
Best drag book (after Hoerner): "Personal Aircraft Drag Reduction", Bruce Carmichael. Private publication, out of print, try some air show booksellers for a used copy.
Best car aero book: "Race Car Aerodynamics", Joesef Katz. More focused on design for downforce, it does blow up a lot of myths that non-aero car racers have about car aero. It also illustrates separation vortexes behind common configurations. I'm hoping for an update in a year or so now that Indy and LeMans cars have gone to low-separation tails to make up for radical HP reductions from 2011 to 2012.
Best pure wing book: "Theory of Wing Sections", Abbott and Von Deonhoff. THE definitive collection of air foil and wing data from wind tunnel testing done by NACA, post war.
There is currently no good reference on the details of interference drag and how to cure it. I do this for a living, and most of the information available besides the experimental evidence of one design being worse than another is simply wrong. For a modern look at how we reduce interference, look at the fuselage and nacelle interfaces of late model business jets, and the wing-fuselage-engine pylon interfaces of the 787, 747-8, and 737NG. This is an area where Boeing has a significant edge over Airbus.
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Off to the Scottsdale Airport :-D
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I have a foto of Thrust breaking the sound barrier from above, the dust cloud [shock wave] goes straight out at right anglels from the sides from front of streamliner for a great distance.
Do any of the CFD programs show the same results?
JL222
Yes, any decent CFD can show compression and expansion waves on a really bumpy and poorly designed object. However, the pressures associated with all of that transonic separation and flow turning can be off by a factor of 10 in local areas, which is why it would be better if all of these teams would area rule the designs before going to the effort and expense of CFD just to see that, yes, bumpy cross sectional area distribution makes lots of shocks. Shocking.
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Eric,
I guess that it is time for me to put in my two cents worth on my favorite aero book "The Leading Edge" by Goro Tamai. I know it is about cars that do not run over 60mph but the aero info does translate to what we are interested in and he does address interference drag, especially junction flows, appendages, fillet radius' etc. It also addresses most of the things that are important to land speed racing related to aerodynamics.
I 1997 or 98 my son and I were at the 5 mile mark when Don Vesco came through at 439 mph in his turbine car, at that time the air inlet to the engine was a scoop that was mounted on the top of the car above the boundary layer. The day was somewhat humid and we could see shock waves coming off of the back of the air scoop. Does your statement " yes, bumpy cross sectional area distribution makes lots of shocks." explain what we saw?
Rex
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Eric,
I guess that it is time for me to put in my two cents worth on my favorite aero book "The Leading Edge" by Goro Tamai. I know it is about cars that do not run over 60mph but the aero info does translate to what we are interested in and he does address interference drag, especially junction flows, appendages, fillet radius' etc. It also addresses most of the things that are important to land speed racing related to aerodynamics.
I 1997 or 98 my son and I were at the 5 mile mark when Don Vesco came through at 439 mph in his turbine car, at that time the air inlet to the engine was a scoop that was mounted on the top of the car above the boundary layer. The day was somewhat humid and we could see shock waves coming off of the back of the air scoop. Does your statement " yes, bumpy cross sectional area distribution makes lots of shocks." explain what we saw?
Rex
I haven't seen "The Leading Edge", if we see each other at Bonneville this year I'd like to get a look at it. Is it still in print?
The speed of sound at Bonneville under the racing conditions of the various meets of the last half century range from ~1100 fps for the 43F during Blue Flame's return run to ~1150 for a rare 100F day. Given this Turbinator's exit speed of 470 mph (691 fps) would translate into M.60 to M.63. This is certainly high enough to see some areas of abrupt curveture develop supersonic flow. This would lead to compression waves on the front end of these areas as the local flow accelerates beyond M1.0 and expansion waves behind as the supersonic flow turns to fill in the downstream pressure recovery area.
Looking at the pictures on the Vesco site, it appears that the increase in area on the front side of the scoop was smooth enough that any compression waves would be spread out and not visible as an atmospheric disturbance. The back side of the scoop is pretty abrupt, so what was likely seen was the expansion wave from the flow turning to fill in the separation area.
The best visible example of this effect in LSR was the famous TSSC photo. Look at the shock that comes from the back of the engine nozzles: There was 39 ft2 of base drag in this area and it caused a large and VERY high drag expansion wave at a completely different visible angle than the compression waves from the other area-increase features (nose, inlets, cockpit) and the trailing expansion shock at the tail.
On a properly designed supersonic vehicle, not compromised by poor aerodynamics, there should be one compression shock spread over the front half of the vehicle and one expansion shock spread over the back half with hard shocks only at the front and rear. This series of compression-expansion-compression waves on the analysis of the current vehicles should have been fixed long before CFD. Some will say that this is impractical on an LSR vehicle. Not true. I solved that problem 3 years ago and we've been working on other issues since.
Got a little off topic here. Good to have a board just for this subject.
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Eric,
The "Leading Edge" is still in print, as a matter of fact I think there is a new edition. I bought mine at the Automotive Book Store, on Magnolia Blvd in Burbank, but it is available through Amazon also. I will remember to bring mine to Bonneville and we should try to meet at the Salt Talks or I will be in the pit of the number 221 4VFL lakester of Steve Nelsons'.
Rex
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Another good book to add to your technical library is "Fundamentals of Aerodynamics" by John D. Anderson, Jr.
Make sure you have you scientific calculator handy.
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Aerodynamics for Racing and Performance Cars by Forbes Aird, HP Books. Great book, clear, helpful, very little math, dispels lots of myths. I found it through Interlibrary Loan.
Remember Wikipedia is not an expert source, just a public source for people to give such information as they believe in (or want you to believe in) right or not. Thus the wholly incorrect discussion of the Dr. Kamm's rear end, which actually has nothing to do with lopping the end off flat.
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Thanks for telling me about Wikipedia and the other references. A lot of us backwoods guys cannot afford tunnel work and reading books is as good as we can get.
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Design your best idea , streamline it, build it, then justify it! Then build the next one better!
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wobbly...many of the best lsr people did not let the
constraints of a windtunnel get in their way to success...!!..
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Interesting shot of the Airbus A380 Winglet from damaged aircraft at Paris Air Show a couple of weeks ago. Note construction and shape....Maybe I should have posted under Tony's Avatars Thread :roll:
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That's some good-looking tail!
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I think that it qualifies :-D might be a little to wrinkly for Tony though 8-)
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And she has a NPL. :evil:
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My Goodness!
The tail's fracture lines seem to match some other lines on the young lady's countenance.
Science following nature, no doubt.
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Nice piece of tail! [Sorry, Couldn't control myself].
Doug :cheers: :cheers: :cheers:
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European hips are great. :-P
Steve
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Interesting shot of the Airbus A380 Winglet from damaged aircraft at Paris Air Show a couple of weeks ago. Note construction and shape....Maybe I should have posted under Tony's Avatars Thread :roll:
AWWRIGHT, what gives, I've stared at that pic for hours, and I still can't find any airbus parts! :x :-D :-D
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Guess we all know what distracted the Airbus pilot! :-o
Remember to gawk responsibly! :-D
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The latest Ferrari F1 car is much faster than before. New aerodynamic shape may be a big factor. A picture of the car is in the attached article.https://www.bbc.com/sport/formula1/49781160 (https://www.bbc.com/sport/formula1/49781160)
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An interesting article about F1 car aero. https://www.bbc.com/sport/formula1/50222105 (https://www.bbc.com/sport/formula1/50222105)
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An article about air flow under the body and behind the tires.https://www.bbc.com/sport/formula1/47838557 (https://www.bbc.com/sport/formula1/47838557)
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I have that allready . It just needs to be wider to fair in my legs. I guess the next question is . Fo a tail sectionwould a verticle blade or a point be better?
This could depend on other things. For example, if the tail needs to provide much stabilization (like fletching on an arrow),
more area would provide more. If speeds are low enough that the vehicle is very, very stable, then a point would be slightly
more aerodynamic. I don't think it would matter much either way, as so many other variables are in play. Based on what I've
seen, Rob Freyvogel's Carbiliner is -- I mean "was" -- one of the most aerodynamic vehicles I've ever seen. I say "was" because he crashed the car. I don't know what caused the crash. Good luck.
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This could depend on other things. For example, if the tail needs to provide much stabilization (like fletching on an arrow),
more area would provide more. If speeds are low enough that the vehicle is very, very stable, then a point would be slightly
more aerodynamic. I don't think it would matter much either way, as so many other variables are in play. Based on what I've
seen, Rob Freyvogel's Carbiliner is -- I mean "was" -- one of the most aerodynamic vehicles I've ever seen. I say "was" because he crashed the car. I don't know what caused the crash. Good luck.
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I think the last word was that Rob probably ran over something on the course.