Aerodynamics of Beam Wings and Crash Stuctures

[PlatinumZealot]

Why can't you guys see this? It is Newton's second law!

Here see it... this is from a steam turbine. It's a bucket. The profile is not an air-foil, it simply operates on impulse. Simply, the gas hits it and it turns. Looks like a curved crash structure don't it?



You see what you shelly and diesel and myurr are trying to tell me is that, by creating a floating beam wing you will have to lower the crash structure. And the rain light has to be in the same place... duuuh. that is obvious.. I am not arguing this!

I am stating the fact that the curved crash structure apart from coupling to the beam wing... ALSO has an individual contribution to the down-force. So it is a double whammy... as I said before... No need for argument. it's a fact!

[bot6]

n_smikle, how much downforce do you think that curved crash structure brings to the car, relative to that car's total downforce?

Would you agree that it is probably a very small amount? And with the upwash caused by the beam wing and the rear wing "bending" the flow coming onto that crash structure, the downforce caused by the crash structure itself is probably minimal due to it having basically no angle of attack in the surrounding flow?

[nacho]

That's how fast cars are made, they have all the little details finished that generate that little extra downforce when summed up.

[Owen.C93]

Impulse will create some downforce, but it will also be draggy so it's not very ideal. If anything it will just be extending the diffuser slightly and the beam wing.

[Formula None]

Why can't you guys see this? It is Newton's second law!

Here see it... this is from a steam turbine. It's a bucket. The profile is not an air-foil, it simply operates on impulse. Simply, the gas hits it and it turns. Looks like a curved crash structure don't it?

http://farm2.static.flickr.com/1092/548 ... 9cca90.jpg

You see what you shelly and diesel and myurr are trying to tell me is that, by creating a floating beam wing you will have to lower the crash structure. And the rain light has to be in the same place... duuuh. that is obvious.. I am not arguing this!

I am stating the fact that the curved crash structure apart from coupling to the beam wing... ALSO has an individual contribution to the down-force. So it is a double whammy... as I said before... No need for argument. it's a fact!

Actually, that is an airfoil, in effect. Anyway, we're not talking about breaking laws of physics, but the efficacy of the CS as a lifting body.

As far as comparing turbine bladesto a crash structure goes, two words: aspect ratio.

[PlatinumZealot]

That is a bucket (a type of blade).

[Formula None]

Didn't say it wasn't, I was pointing out that it has an airfoil cross section. And it has it along a decent span, so it can do some work efficiently, not the case with the CS. Again, what Ferrari/Williams have is basically what the CS looks like when its not attached to anything. Its simply a loft shape that can't reduce width or height (back to front) and must rise from the back of the gearbox up to the safety light.

We need to wrap this topic up or its going to get split off into the most boring thread on this forum.

[PlatinumZealot]

By definition you can call it an aerofoil yes, but when I say airfoil I mean in the sense of a plane wing. A bucket blade doesn't make lift like a plane wing or downforce like a wing. That type of turbine blade doesn't have the cross section of a plane wing.

It makes all of it's "lift" in the opposite direction of the fluid leaving it. It uses drag to turn. Impulse.

A plane wing makes the lift almost perpendicular to the fluid direction. You want to reduce drag in this case.

You see now?

Two VERY difference phenomenon.

You see them combine these two methods in the Monaco Spec wings.

[bot6]

Mate, I'm sorry but a turbine wing does not use drag to turn.

By the way, both a bucket blade and a turbine foil create most of their lift in similar ways (indeed the momentum conservation law), but in the case of the crash structure, its lift creation is minimal because of

1) its low cross section

2) its non existent angle of attack (it might seem angled compared to the motion of the car, but with the upwash caused by the rear wing and beam wing, the local flow is basically parallel to the crash structure at that precise spot)

3) the fact that with such a small span and with rounded edges, and no endplates, the pressure differential between top and bottom is very small because the air goes around the crash structure too easily, so it would be extremely inefficient at creating downforce.

That precise Ferrari design is there just as an attempt to minimize the drag caused by the crash structure, by shaping it in a way that stays as parallel as possible to the local flow.

Now maybe we could stop talking about bucket wings because it's starting to pollute the thread and it's completely irrelevant to the F150 (Yes, I'll keep using the old name!!! Screw Ford).

[SiLo]

For all intensive purposes, the curved crash structure will create a small amount of downforce, which could be considered negligible to the total amount of downforce created by the entire car.

End of.

[PlatinumZealot]

Mate, I'm sorry but a turbine wing does not use drag to turn.

By the way, both a bucket blade and a turbine foil create most of their lift in similar ways .

... I does use drag/thrust (whichever way you want to put it) almost exclusively..

OK... stop and take two breaths.. Now - Get yourself educated on Newtons second law. http://en.wikipedia.org/wiki/Newton's_l ... on#Impulse

Then go and read a turbine book. Sorry.

You know what let me get you a picture.



you see, the bucket blade is nothing like a plane wing. It's a bucket. it uses almost elusively impulse to turn. The "force" (thrust or whatever i do not want to use the word lift here) acts parallel to the fluid flow at exit. That does not happen in aeroplance wing where the lift force is perpendicular. Got that?

edit: again.. notice I say "parallel" please don't take it literally. there is a exit angle of the fluid in the bucket turbine blade.

[bot6]

Again, a little politeness would go a long way. "unforgivable rubbish" could just as well be replaced by "I respectfully disagree". Which I do, by the way.

What you are saying all depends on the definition of lift/thrust and drag, which depends on the definition of your axis system, which depends on if you are considering global flow in the turbine or local flow on the foil.

The fact that you are mixing drag and thrust shows that the main problem here is that you do not define the terms you use rigorously. We might actually agree on the basic physics while keeping on arguing because we use the same word in different ways.

And on top of that, the turbine discussion is completely irrelevant here.

I think we need to get back to the original point, which is the downforce caused by the crash structure.

I think you will agree that the limited cross section of the crash structure and its rounded edges makes the effective wing span of that part relatively small. So the downforce created by it would also be fairly limited. Right?

Now add to that the fact that the beam wing close by, and the rear wing, cause a sizable change in the direction of the local flow (generally termed an "upwash"). The local flow is therefore close to parallel to the crash structure, so the local angle of attack of the crash structure to the local flow is very small. Hence, again, very limited downforce.

Add both effects, and you will have to agree that the amount of downforce caused by the crash structure is fairly small?

Oh and by the way, I think I know a bit about Newton's second law, with two master's degrees related to fluid dynamics and a few years of experience in the field. So next time, please keep your comments about me needing "educating" to yourself. Thank you.

[PlatinumZealot]

If you really want to know, Yes. I do not use those terms rigorously because it depends on your point of view.

Drag is generally what opposes the work that you trying to do, and is caused by friction if the fluid or whatever parts in the machine and the dynamics of the fluid itself. Agree?

Now..
In a turbine the fluid is doing the work... Do you call it drag or thrust? That depends. But if you check it out it's all resolved in the same direction. So when I do my turbine calculations I am not so hung up about those two words, because they don't change the resulting force on the blades. It's just me.

I do not know why you say it is irrelevant, I think it is, because there is an obvious change of direction of the fluid over the crash structure. There is only ONE result of a momentum change. IMPULSE. I had to bring up the impulse turbine to let you realise that impulse is used to generate force and especially where fluid conditions are very turbulent. The first stage of a steam turbine is usually an impulse stage. The same for a turbo charger.

You can see the impulse stage, then the reactive stage. (ignore the guide vanes)


So yeah using impulse to generate downforce is actually good especially if you are dealing with a turbulent environment. That's why Monaco spec wings are so bucket shaped. Raw downforce from momentum change.


I do not know how much downforce a curved crash structure contributes. do you?

I don't care how many degrees you have. If you checked your fluid dynamics book, I'm sure you will see what I am telling you in chapter 1 or chapter 2.

[bot6]

We all agree that changing the direction of the flow in the right direction will create downforce. That is what you call impulse, or what I call momentum conservation.

The point I am making is that the local flow is already "bent" upwards by the beam wing and rear wing. So the crash structure is basically parallel to the local flow. So it does not change the direction of the flow, it is just shaped to go along the flow.

This is the last post I will write on this subject. If you keep omitting the main point because you just wish to talk about turbines, then that's your choice. But you should do that on a turbine forum, not an F1 one. Or at least wait until they reintroduce the turbo.

[myurr]

n smikle - I think we all get the basic theories behind what you're saying, but skipping all the way back to my first arm chair aerodynamicists post on this matter then I was basically saying what bot6 has more eloquently stated. That in isolation the crash structure would generate a bit of downforce. Probably not a significant amount, but worth doing.

However the structure is not run on the car in isolation. There's a blooming great beam wing just above it that is already deflecting air in that region in the same direction the crash structure happens to curve.

So it comes down to this - When taking into account the local flow of air as created by the beam wing, rear wing and diffuser, do you think the crash structure deflects enough additional air to produce a reasonable amount of downforce?

The thing to bear in mind is that this all started as yet another bash McLaren thread with people saying that McLaren were stupid and going to lose because they didn't implement the same rear end design as some of the other teams (despite them running a similar floating beam wing a couple of years ago). So in these terms a reasonable amount of downforce, to me, is enough to produce a measurable difference in lap time - whatever that may be.