Swept Volume Theory

You say that air cannot move instantly to fill the void behind the sail. What mechanism prevents this if not inertia (momentum) of air particles? That is what I mean by Newtonian mechanics.

 

The "standard" Newtonian momentum theory only explains the force on the lower (windward) side of the aerofoil. It doesn't explain the source of the low pressure above the upper surface, so I don't understand where you are going with this post.
SVT explains the source of both the high pressure below (to windward of) and the low pressure above (to leeward of) the aerofoil.

 

The only place I have ever seen it suggested that there is an issue with explaining curvature over the top face of an airfoil is the SciAm article you linked to, and it is pretty clear that most of us here consider that to be bunk.

The Coanda effect explains why the flow stays attached (at least enough for a lay explanation that we are after here), and then conservation of momentum (Newtonian) explains the low pressure and upwards thrust on the top surface of the wing. You will probably point out that I am introducing another effect which is true, but it is also a real, observable, valid property of the world we live in.

 

Again a misinterpretation. Where in the SciAm article does it have an issue with explaining curvature?

No. The Coanda effect does not explain "why" the flow stays attached. It merely describes the effect. There is no explanation of the cause.

 

I believe this statement is false. Please provide a reference to this claim so it can be debated logically.

 

The Coanda effect is trivial to explain from first principles - entrainment of air beside the stream creates a low pressure region. This cannot be relieved by fluid moving in from distant regions if the stream is adjacent to a surface. Hence the stream is pulled towards the surface by the area of low pressure.

If the free stream direction is horizontal and air follows a convex curved upper face of a foil such that the local stream has a downward velocity component (in the conventional layout of these situations) then the air now has a vertical momentum component. An impulse must have been applied to achieve this change of momentum. You can ignore pressure differences and simply apply an equal and opposite momentum change to the foil, or you can show that the curvature of the streamline must result from a non-uniform pressure field above the foil (i.e. ambient pressure at distance decreasing to some minimum at the surface). Thus there is low pressure at the top surface of the foil.

The principle that necessitates low pressure on the top face are precisely the same as that which necessitates high pressure on the bottom face: a change of direction of the flow. It is perfectly possible to reframe this in a reference frame following the free stream as you have done, but what does that bring which is novel?

 

Not only do I have to chide you once again for introducing a novel concept into the argument but I have to correct you on your use of it to object to the Swept Volume Theory (SVT).
According to Encyclopaedia Britannica, the "entrainment" is explained as:
"When the supply of these molecules is limited by an adjacent surface, a partial vacuum develops between the jet and the surface."

The Coanda Effect does not explain how that partial vacuum develops, it just explains that a partial vacuum develops.

The SVT explains how that partial vacuum develops on the convex (leeward) side of the sail.

 

No, I'm not changing the FoR to the "free stream". The undisturbed air is not a "stream". The undisturbed air is stationary, static, the reference from which to observe the relative motion of the airfoil. Using the term "free stream" indicates that you have not yet grasped the concept of a different FoR.

What is novel is that in this FoR the source of the pressure gradients can be explained in using the Gas laws without consideration of fluid flow or momentum change.
All the failed explanations use the foil's FoR and get hopelessly tangled up in fluid dynamics and momentum change.
100+ years of fluid dynamics and momentum change theory has failed to predict the size of the pressure gradients, whereas I believe that the skilled application thermodynamics on the new FoR will succeed.
But for now the significance of being able to discard fluid dynamics and momentum change to explain the cause of the pressure gradient presents a framework from which to start to build a true understanding of the nature and size of the aerodynamic force.

 

What utter trash!

Would you call results like this a failure?
(From Analysis Of Turbulent Boundary Layers, by Tuncer Cebeci & A.M.O. Smith. Almost 50 years ago!)

 

Not sure, but if the y-axis (Cp) is a coefficient of pressure, then there's a heck of a discontinuity at 0% chord, where Cp goes from 0.8 to -2.0!
I'll get hold of the reference and see what it's all about.

 

No discontinuity - just a steep gradient between the stagnation point at the leading edge (where Cp=+1.0) and the point a short distance aft on the upper surface where the flow speed is maximum (Cp = max negative value).

Notice that all three curves (the inviscid calculations, the viscous calculations, and the experimental data) show the same thing

You don't have to look at that specific reference (It's a book.). Literally every airfoil will show the same trend, at least at angles of attack large enough to overcome the effects of whatever camber the foil has.

 

You are arguing frames of reference. They are not significant. The choice of frame of reference is normally done to simplify equations. You are trying to railroad the discussion with irrelevant arguments. For example, chiding members for "introducing novel concepts". Why do you think you have the right to limit any concept that proves you wrong? That is simply an attempt to censor facts that prove you wrong.

 

Listen to Admiral Halsey....

 

I have plotted the "test data" with the lower surface as negative % to clearly demonstrate that yes, actually that is a discontinuity.

Please, show us one with a discontinuity of pressure (or even a steep gradient) at the stagnation point.

Yes, actually you do.[edit] Maybe you don't have to, but it's quite a good idea to look at it if it is being introduced as evidence. [/edit] It's quite enlightening.
The book is a very obscure (no copy in State library, only Uni) and contains a very telling sentence in the Preface:
"When the authors think about this situation, they cannot help but feel a strong sense of luck, for there is nothing fundamental now known that explains why these engineering approaches succeed as well as they do."
It clearly does not demonstrate fluid dynamics' ability to predict the size of the pressure gradients.
You have quoted the chart entirely out of context.

 

Making invalid statements doesn't progress the argument.
My whole theory is based on changing the frame of reference. That is the reason that it is significant.
While the choice of FoR may be "normally done to simplify equations", that is not the case in my theory. I change the FoR to demonstrate there is no fluid flow.