Is circulation real?

I would like to know what a "thought experiment" is.

 

And where does your "F = Mdot x a " appear in that discussion, or have anything at all to do with the current subject?
We're talking about the aerodynamic force from the wind over a sail.

 

If you're struggling with that you really haven't been following the conversation. Paste gedankenexperiment into your favourite search engine.

 

Now that we have identified "Mdot"as mass flow rate:
,
It's pretty obvious that Newton had nothing to do with " F=Mdot x a "
Just check the dimensions:

 

I contend that you cannot measure your mass flow rate with any degree of accuracy. As I have said, to measure the mass of the gas you have to measure the volume, and since there is no pipe nor is there a quasi-containment boundary, there is no possibility of even making a wild guess of the mass of air being accelerated.

 

You are missing the point completely. You do not have to quantify the amount of mass that the sail accelerates by changing the velocity direction. AS I STATED QUITE CLEARLY, it is more than likely impossible to quantify it.

So I am questioning your wording "I contend that you cannot measure you mass flow rate with any degree of accuracy" you need to add on "with respect to a sail" Other situations, the mass flow rate can be determined

You obviously have not taken any university courses that deal with the design of vane machinery. Pumps, compressors, turbines, stators etc. or you would have had specialists in the fluid field use the formulas. While you have disregarded
NASA in other posts, you should realize that the engineers of jet engines

• General Electric. GE Aviation, part of the General Electric conglomerate, currently has the largest share of the turbofan engine market. ...
• Rolls-Royce. ...
• Pratt & Whitney. ... etc

would use advanced computer assisted programs to design these engines, and the next time you get in a Boeing, you should hope that they got it right

The inability to quantify the amount of the mass of air that a sail deflects/re-directs does not make the equations inapplicable. The development of equations, proof and experimentation is certainly done with finite control boundary's.
Often when developing the lift/force of vanes, a stream of air/fluids/gases from a nozzle is used, with known mass flow rate and velocity.

In engineering, sometimes calculating accurate numbers for insertion into equations is not possible. Take for instance a beam where it is under a multitude of loads, torsion, shear, perhaps some dynamic loading that creates stresses
that cannot be determined by equations. Statically or dynamically indeterminate problems. How do you find out possible locations of failure? Glue on some strain gauges, measure the strain, orientation etc, and working the stresses backward from deflections can show the actual stresses evident with different loadings. I have grossly simplified this process.

The point being is I am only repeating what engineering PHD's have taught. The one component that that causes the wind to produce lift on the windward side of the sail is the change of direction of the air's direction.

It seems to me that you had originally were trying to find out why a wing provides lift and why a sail provides lift.

 

I can't believe I've been suckered into arguments about the mass and volume used in the momentum theory of lift. It's patent nonsense since it doesn't lead to the identification of the pressure differences that are necessary to transfer force from the gas to the sail. And, although it has been an interesting exercise, getting sidetracked by @Barry 's Mdot x a formulation has been such a waste of time.

My fundamental issue is the use of fluid dynamics, and in particular the applicability of the Navier Stokes equation to explain the aerodynamic force.
It contains the elusive "v" (or "u") representing the velocity vector of the gas which, as I have pointed out ad-nauseam, in the case of the wind over the sail, the speed vector of the gas velocity cannot be identified.

The velocity of the gas, in the yawning no-mans's land between the human scale, down to parts of a metre, and the molecular scale of nanometers, has not and cannot be determined by a real or by a thought experiment.

I have pressed this forum to provide evidence to the contrary and have come up empty handed. A theory cannot be proved by science, but it can be disproved.

That's where a new paradigm is required to explain the source of the pressure differences necessary to generate the thrust and leeway/heel force from the wind to the sail.

 

And as I said. If you can't quantify it you can't use it in an equation.
But also, as I have said, I'm not wasting my time debating the momentum change argument.
My issue is with fluid dynamics and the source of the low pressure to leeward of the sail.

 

You can lead a horse to water but you can't make it think.

 

It wasn't particularly funny the first time.

 

The simple application of an MFP calculator (omnicalculator.com/physics/mean-free-path) reports that air, say N2, at NTP has a molecular diameter of 0.36 nm and MFP 70 nm giving a Knudsen Number of around 200.
This is five orders of magnitude above the range of the continuum regime,: Kn<= 0.001.
Does this not cast doubt on the validity of using the continuum mathematics of fluid dynamics, i.e. Navier Stokes, in aerodynamics to model airflow in aviation, wind turbines and yacht racing?

 

47 pages of this nonsense. There must be a better use of most members' time.

 

However, you have not disproved anything. All you have done is shown the extent of your misunderstanding. By your statement, the theory is valid.

 

Early on I rejected the Tooth Fairy, the Easter Bunny and Santa Claus. As I grew up I have also rejected chiropractic, osteopathy, naturopathy, homeopathy, intelligent design, and theology. (The jury is still out on acupuncture!)
The Stirling Engine presented a huge challenge - understanding that the large cylinder was not a piston. Having cleared that hurdle for myself, I derived the greatest pleasure from disabusing my friend John, an engineer and Patent Attorney, of that fact.
I went through a similar process with the Blackbird, understanding that the wheels were driving the prop and not the other way around. And again, I convinced John of the fact so convincingly that we went on to build our own working model.
Reading the Brenner article fuelled my doubts about the issue. At that stage I thought I was only bucking the 120 years of aerodynamics, but this made me realise that we were bucking the whole 250+ years of fluid dynamics.
I have a nephew who is a Supreme Court judge, a polymath, a musician, historian, and the most intelligent person I know. He is also a deeply committed member of the Catholic Church. I know there is no argument I could use to disabuse him of his faith. And he will freely admit, that his adherence to the dogma of the church is based on faith.
Yes, I know that planes fly and gas turbine engines work, but I can not be certain that the aerodynamics of MacLean, Drela, Anderson were directly involved, and I’m not sure that you can either. I believe that the engineering of these devices is based on the tried and true process of continuous evolution: experimentation and trial and error.
On this forum I discern members with intelligence and enquiring minds, competent and engaging people, and I would willingly go to almost any lengths to shake your faith in aerodynamics!
I have tried with all the arguments that swayed me, but they clearly haven’t worked .

What would it take to shake your confidence?

 

I agree, we should not try to disabuse you of your faith. This is Gonzo signing off.