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does anybody believe that we can estimate the pressure around a wing without solving

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Old   February 23, 2010, 10:42
Default does anybody believe that we can estimate the pressure around a wing without solving
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any fluid mechanics governing equations?
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Old   February 23, 2010, 18:34
Default potential methods
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Using potential theory (complex algebra + non conformal transformation) you can do the job.
I did it as a student 15 years ago using a Quick Basic implementation (a very hard job for an exercise); I think that now you can implement it very fast with a MathCAD worksheet...
I will explore the archive; if I find my code I will happy to post it...

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Old   February 23, 2010, 20:49
Default you mean you used potential function? What if no potential theory?
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It means that ironically, people can find pressure without solving those fluid mechanics equations and using those stupid finite element, finite difference methods. To develope various numerical schemes is to waste time.

I am very surprised to find that people have a stereotype that the aerodynamic force is produced by airflow. So they firmly believe that to solve the NS equations is the only way to know the aerodynamic force. But the force is the interaction produced by the relative motion of airplane and airflow. The airflow diverts under the force exerted by the airplane. So people must have another way to estimate the force without solving the governing equations like the Euler equation, the full potential equation, or the NS equations. Essentially, the equations can be avoilded for the force.
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Old   February 24, 2010, 04:26
Default airfoil polar map
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Ok, you are right. If your need is to deal only with forces you can use polar plots (analytical simplified models or experimental ones).
Usually aero-maps are the best choice when you are focused on the effect of the actions produced by a wing.
We have developed a simple flight simulator for a student project: a small biplane made by corrugated board designed for the RedBull FlugTag event (http://www.redbullflugtagusa.com/).
Take a look to this paper:
http://www.pcm.unifi.it/AIAS2008/CD%...i_paper201.pdf

However if your are concerned with the mechanism that generates down forces and drag (in this case for racing car applications) you will have a substantial benefit using CFD simulations.

We have used mesh morphing (http://www.rbf-morph.com/) for the minimisation of the drag force of our land speed record go kart (http://www.torvergata-karting.it/fil...008_CARENA.pdf).

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Old   February 24, 2010, 23:10
Default Thanks Meb, but I don't understand Italian.
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The diagrams look very nice though.
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Old   February 24, 2010, 23:46
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So I'm confused - how do you propose getting the force? What if the airfoil flow is separated? What if friction drag is important? You rule out using the Euler equations, the NS equations, and potential theory, so what do you recommend in their place?
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Old   February 25, 2010, 04:51
Default Ita 2 eng
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Go here:
http://translate.google.com/
and load the document... You will lost the figures but you will understand the text.
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Old   February 25, 2010, 10:11
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adg, where do thouse governing equation come from? the conservation laws and Newton's laws. We use them instead of solving the equations.
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Old   February 25, 2010, 10:54
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So you are dismissing the governing equations, and then appealing to the same governing equations - now I'm wondering if I'm the confused one.
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Old   February 25, 2010, 10:56
Default we use the conservation laws not those governing equations.
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Those governing equations are some ways of describing the conservation laws. But they are not the only ways we can make use of.
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Old   February 25, 2010, 10:58
Default we can use the conservation laws and newton's laws to find the pressure.
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we don't need to solve those governing equations.
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Old   February 25, 2010, 11:06
Default help us
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Help us with an example.
I have provided links to a paper about the use of wing forces. Give more details!
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Old   February 25, 2010, 11:39
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Yes - I too would be interested in the governing equations you recommend we use.
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Old   February 25, 2010, 11:43
Default gentlmen, I just survey how many people believe that we can get
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pressure around a wing without solving those stupid governing equations. I didn't mean to convince you to believe that.

If you're now devoting your time in developing numerical schemes to solve the governing equations, you might be wasting your life.

Sorry! The fact can't be easily accepted but it is true.

Recall that who tell you to solve the governing equation is the only way we can do to get the pressure. Nobody. But in our universities, everybody is doing like this. So it is widely accepted. So it is implanted in our mind unattentionally. Right now, to get rid of it or to update your mind becomes a hard thing.

To develop a new approach to get pressure might be easier than to develop a new numercial scheme for sovling the governing equations.
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Old   February 25, 2010, 11:48
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So show us instead of just repeating how "stupid" we are. Put up or shut up. Show me how you get the pressure around a NACA 0012 airfoil at a 15 deg. AOA and a Re = 6 million - just the equations would be sufficient.
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Old   February 25, 2010, 11:57
Default adg, I am writing a software. You can buy it and do it yourself when it
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is ready. Before then, you guys can still use any conventional methods and software, which are not bad choices.

Honestly, I have tested some with NASA airfoils. The results are very satisfactory.
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Old   February 25, 2010, 12:27
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Quote:
Originally Posted by vegbird View Post
is ready. Before then, you guys can still use any conventional methods and software, which are not bad choices.

Honestly, I have tested some with NASA airfoils. The results are very satisfactory.
If I had a dollar for every time I have heard some variation of this theme, I could have retired years ago. Look, either you are using a DATCOM-like approach, involving copious amounts of empirical data with some physical reasoning and curve-fits, or you are depending on the self-same equations of motion you have previously derided. If you really expect to be taken seriously, present some framework of your approach and let it be debated openly. When you have something meaningful to present, then I'll be more interested.
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Old   February 25, 2010, 13:03
Default agd, I know it is very hard to update one's mind because I have
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been struggling my brain where has be washed for a long time with those printed in text books.

I can't post any mathematical formulation for an open debate since it has a lot commerical interest. Imagine a new accurate and fast scheme will bring Ansys or Flow3D how much benefit and market occupation? But I do use the conservation laws and equations different from those given in our classes. The most important thing is I use a different approach from the ones taught in universities.

Now in my eyes, those spending their all life in developing finite element methods, finite difference methods, or finite volume methods are wasting their time. They have no other choices but doing it.

If you are really interested in it and you are a good investor (like those in Wall street), we better talk in person. haha.... Otherwise, please see this talk as a joke. But it is not a joke. It's really happened in somewhere on this planet. Sorry can't offer you more details.

Again, to update one's mind is really one of the two hardest things in this world. The other is to convince other people.
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