FloViz Interpretation

[hardingfv32]

While the endplate could play a roll, the pattern we are seeing is generally very symmetrical on either the end plate side or non-end plate side of the double fence installations. You would have to provide some info on the possible effect on fence flow with endplates before I would find it relevant.

What do you propose as the purpose of the fences?

Don't most of the 2012 wings have central fences? Are you referring to double fences?

Brian

[flynfrog]

You can clearly see that it is not helping to keep flow attached. It seems F1 Tech has been hit by Vortex fever once again.

While I agree that the FloViz does not represent what we think is 'attachment', it must be remembered that we do not have much, if any, knowledge about how FloViz should look like in these types of applications.

Using the McLaren red second element as an example:

1) Fact... Fences on wings with high AoA promote attachment.
2) This second element is at a high AoA.
3) What other reason could there be to add these fences?

If you therefore assume that the fences are there to promote attachment, then can we presume that the FloViz pattern (V shape) we see is that of a vortex promoting flow attachment? Is this logic flawed?

Brian

I do have a pretty good grasp what flo viz should look like do you?
1. Fences on the edge of wings keep your pressure differential from spilling over giving you a larger effective area of the wing. Fences in the middle of the wing will reduce the effective area due to the vortices produce by the air detaching. Adding them in the middle of wing will also be much worse in YAW

2. true

3. Trying to separate pressure regions across different parts of the wing ? The over all net gain is probably more than the loss from the flow separation.

[hardingfv32]

Trying to separate pressure regions across different parts of the wing ? The over all net gain is probably more than the loss from the flow separation.

I understood this to be a form of attachment improvement. 'Cross flow' was detrimental to attachment.

Feel free to expand.

Brian

[flynfrog]

fences are used on swept wings to limit the sideways flow to help prevent the entire wing from stalling at once F1 wings are not swept. This may just be the least bad solution to the slot gap separator.

[hardingfv32]

Discussion of the slot gap separator has no relevance to the discussion of the bottom of the main RW fences. A slot gap separator is only required in a small region between the main and second elements. Absolutely no requirement to extend the slot gap separator to the lower surface of the main element.

The fences have been added to the wings to provide some kind of aero benefit.

Brian

[Cam]

@ Cam My unreserved apology to you.

@Gato

finding scientific resources on this exact subject, using the exact type of paint, material, curves etc is impossible. In fact, finding any real scientific information on these topics (others relevant to this forum), that is zero cost and publicly accessible, is very, very difficult. What I, and others, are trying to do is give a cross section of similar relevant information in the hope the the combination of the whole will assist and help us find the answers we're all looking for. Most people here just give opinions, and that's fine, I'm more of a scientific man and like to see facts and figures that are repeatable as evidence and that is why I show scientific papers (when I can find them).

I have several more to show:
• Application of Pressure-Sensitive Paint to Low-Speed Wind Tunnel Testing at Japan Aerospace Exploration Agency
http://www.icas.org/ICAS_ARCHIVE_CD1998 ... RS/459.PDF
• Surface Flow Visualisation of Separated Flows on the Forebody of an F-18 Aircraft and Wind Tunnel Model
http://www1gtm.nasa.gov.speedera.net/ce ... H-1481.pdf

Now, I know these are not F1 struts, slots and DDRS (the F-18 paper is cool though) although now these 2 show the paint and the application and effects in real world on a jet. Again, in the hopes that the combined will make the whole.

BTW, I have no problems with being called on my posts, that is why we are here, to question, to listen and to learn.

[flynfrog]

Discussion of the slot gap separator has no relevance to the discussion of the bottom of the main RW fences. A slot gap separator is only required in a small region between the main and second elements. Absolutely no requirement to extend the slot gap separator to the lower surface of the main element.

The fences have been added to the wings to provide some kind of aero benefit.

Brian

well in that case it must be a super conda vortex blown exhaust fence.

If you look up at my previous post this maybe be the least bad way to add in the slot gap separators. They could have had issues between the elements that were solved by extending the fences. The truth is we cant tell from the floviz we can only tell that there is a rather large separation on the bottom of the wing. Trying to get more out of this than that is grasping at straws you cant see.

[gato azul]

Are you referring to double fences?

yes, I did, in the context that you said, they are definitely a benefit.
If this is the case, and you said or assumed earlier that the flow pattern on the MCL wing/flap was "what they wanted",
I ask, why in your opinion have many (most/all?) teams gone away from the dual "fence" (slot gap separator), to a central
one this year.

If this "fences" are so beneficial in terms of keeping the flow attached, more should be better - no?

I think Flyn made some good&valid points in regards to the use/benefit of "fences" on some aircraft wing configurations.
A endplate/winglet by itself will reduce cross flow tendency along the wingspan, this was why I pointed out that in your
example (paper) the wing did not have one.
Therefore any effects (positive or negative) could be different if you use them in a different configuration.

I guess, what I want to say, is keep the aspect ratio and the "loading" of the wing in mind, when you compare it to aviation wing data / tests.
A F1 (race car) wing is quite specific, and not all effects involved "scale" well, so drawing conclusions from one application to another can be misleading at times.
So before we go and "hand out the chocolate" for "absolutely right" to early, mind about it in a bit more detail and from some different perspectives.
I'm not trying to dig on or belittle anyone here, far from, just want to prevent people from jumping to conclusions to soon, that's all.

Enjoy the debate

[gato azul]

In fact, finding any real scientific information on these topics (others relevant to this forum), that is zero cost and publicly accessible, is very, very difficult.

BTW, I have no problems with being called on my posts, that is why we are here, to question, to listen and to learn.

All good mate - no problems, but I guess most people on here would know how to use google, when they have a real interest in the deeper understanding of the subjects. Just as you do.

Don't worry, I will not bother you any longer.
I like and appreciate your enthusiasm - I really do, but maybe sometimes less (and more specific information) is more (valuable).

Keep up the good work !!

[hardingfv32]

If you look up at my previous post this maybe be the least bad way to add in the slot gap separators. They could have had issues between the elements that were solved by extending the fences.

How can fences on that extend all the way to leading edge on the bottom of the main element possibly have any effect on or with the slot gap separator on the top surface. The use of fences on the RW fits perfectly with the stated design benefits of a wing fence.

What evidence or visual clues do you have that would indicate that these are anything but wing fences? What causes your doubt?

Brian

[hardingfv32]

If this "fences" are so beneficial in terms of keeping the flow attached, more should be better - no?

Of coarse a wing fence promotes attachment on high AoA wings. We do no know where along the high AoA continuum that the F1 wing lies. Maybe some F1 RW installations are prone to more attachment problems than others. If you have no attachment issue a wing fence is not going to provide any benefit.

In the case of the Lotus RW main element lower surface we have an object that meets all the design criteria of a wing fence. If it is not a wing fence then what is it? What evidence or visual clues do you have that would indicate that these are anything but wing fences? What causes your doubt?

Brian

[flynfrog]

If you look up at my previous post this maybe be the least bad way to add in the slot gap separators. They could have had issues between the elements that were solved by extending the fences.

How can fences on that extend all the way to leading edge on the bottom of the main element possibly have any effect on or with the slot gap separator on the top surface. The use of fences on the RW fits perfectly with the stated design benefits of a wing fence.

What evidence or visual clues do you have that would indicate that these are anything but wing fences? What causes your doubt?

Brian

I don't think I ever said they were not wing fences. They are also extensions of the slot gap separator. You stated that they were there to keep flow attached. You have been told by more than one person that the floviz tells a different story. Fences are normally used on a swept wing where you have a pressure difference the long ways across the wing. An f1 wing is not swept a fence is not going to work the same way it does on a swept aircraft wing. My guess is the slot gap separators are causing an issue across multiple elements of the wing and this is the way of dealing with that. You don't understand what a fence is doing you have simply read that it helps keep a wing from stalling without understanding why.

[hardingfv32]

They are also extensions of the slot gap separator. You stated that they were there to keep flow attached. You have been told by more than one person that the floviz tells a different story. Fences are normally used on a swept wing where you have a pressure difference the long ways across the wing. An f1 wing is not swept a fence is not going to work the same way it does on a swept aircraft wing. My guess is the slot gap separators are causing an issue across multiple elements of the wing and this is the way of dealing with that. You don't understand what a fence is doing you have simply read that it helps keep a wing from stalling without understanding why.

Please help me to understand how the wing fence function. I thing I have seen through the use of a vortex and the control of 'cross flow' (flow control). Is 'cross flow' detrimental to flow attachment?

That fact the wing fences are usually found on swept wing aircraft does not preclude their use on F1 wings. The aspect of flow attachment through vortex generation seems valid in the case of F1 wings.

If the slot gap separators are causing trouble, then what name or design feature do you assign to these things that look like 'wing fences'? I wish to research them. I am trying to get an understanding of the types of design features that the Lotus duct is supposedly dumping flow on.

Brian

[flynfrog]

They are also extensions of the slot gap separator. You stated that they were there to keep flow attached. You have been told by more than one person that the floviz tells a different story. Fences are normally used on a swept wing where you have a pressure difference the long ways across the wing. An f1 wing is not swept a fence is not going to work the same way it does on a swept aircraft wing. My guess is the slot gap separators are causing an issue across multiple elements of the wing and this is the way of dealing with that. You don't understand what a fence is doing you have simply read that it helps keep a wing from stalling without understanding why.

Please help me to understand how the wing fence function. I thing I have seen through the use of a vortex and the control of 'cross flow' (flow control). Is 'cross flow' detrimental to flow attachment?

That fact the wing fences are usually found on swept wing aircraft does not preclude their use on F1 wings. The aspect of flow attachment through vortex generation seems valid in the case of F1 wings.

If the slot gap separators are causing trouble, then what name or design feature do you assign to these things that look like 'wing fences'? I wish to research them. I am trying to get an understanding of the types of design features that the Lotus duct is supposedly dumping flow on.

Brian

When a wing sees cross flow the effective air speed across width of wing fwd to aft can drop below the stall speed causing an aircraft to crash. A fence can help stop this. It does not come without trade offs it reduces the effective area of the wing at it gets even worse in Yaw. Once again the fences and the slot gap separators in this case are one in the same.

The "duct" on the lotus has nothing to do with the fences on the STR. They are probably taking an area of higher pressure and blowing the wing in one way or another to try to keep a flow attached at a higher AoA or they are trying to shed some drag.

[hardingfv32]

Once again the fences and the slot gap separators in this case are one in the same.

The "duct" on the lotus has nothing to do with the fences on the STR. They are probably taking an area of higher pressure and blowing the wing in one way or another to try to keep a flow attached at a higher AoA or they are trying to shed some drag.

If they are the same, then we have a slot gap separator that improves attachment and/or controls 'cross flow'. Why would Lotus dump flow on a device that promotes attachment or controls cross flow? Why not run a double slot gap separator system and the have a simple main element bottom surface in the center to route flow to.

The question: Why try to integrate the activities of two system that 'seem' to have opposite design goals?

Brian