Is circulation real?

I am encouraged that you acknowledge the possibility that a realm of science exists to be discovered.
Whether or not the new realm can be developed sufficiently soon to make me a better sailor will only become apparent in the fullness of time.

 

QED

Yet again you have proven your lack of comprehension in the most basic forms - the language in which we are communicating.
No where in my post do I state that I acknowledge anything.

It seems you are seeing things in the shadows that are not really there...

 

Well, you did rather leave yourself open!
But then your response only addressed holistic throw-away, and completely missed the point of my post, summed up in the final two sentences:
"Since the nature of the velocity vector cannot be identified, the N-S equations have no meaning.
@Barry says he never thinks about the molecules. What does he think provides the M in his "So Newton F=Mdot x a"?"

 

Nobody misses the point of your statements, which is to reveal the extent of your self-importance.

 

I may have found the source of confusion about the use of M (mass of air) in the "F=Mdot x a" formulation of the the lift force that acts on the sail from this quote from @Barry in the Swept Volume Theory forum:

The mass of a solid object is easy to identify: You can put the object on a real, or virtual, weighing scale and read off the calibrated value*.
You can't do that with a gas.
In order to determine the mass of a gas you have to have to first contain it. In a real container to prevent the gas from escaping or diffusing into the environment. Only then, can you put it on a weighing scale, and derive the mass of the gas by subtracting the weight of the empty container** from the reported value. It's the containment requirement that separates the gas from the solid. You can't identify the mass of a quantity of gas in a real experiment, or a thought experiment, à la Einstein's gedankenexperiment without it being in a container.
@Barry 's postulate of a quasi containment boundary for this container clearly demonstrates the flaw in the argument. A quasi containment boundary cannot possibly exist in in a real experiment or imagined in a thought experiment.

*The weighing scale measures force required by the scale to counter the force generated by the mass of the object under the influence of gravitational acceleration, g, but the scale in our experiment has been calibrated to account the local value of g.
**The container has to be evacuated prior to using the weighing scale to assess its weight.

 

Your lack of imagination does not make anything invalid. There is no need to contain a gas to calculate the mass. The volume and pressure is enough. To start with, your insistence in "thought experiments" is an oxymoron. Experiments are the basis of empirical knowledge, not of philosophical musing. The results are what they are, whether you understand them or not. Facts exist even when there is no explanation for them. You propose that facts do not exist because you can't understand them.

 

So many problems. I'll just go for the low hanging fruit.
Yes, if we have pressure and we have volume we can calculate the mass, and yes, we can measure the pressure with either a real or a thought experiment.
But there's no experiment, real or thought, that will yield the volume of the air that is supposedly being accelerated.

 

So we are on the same page here. I am going to refer to a mass with a value of X mass units

M with a dot over it in fluid mechanics Mdot refers to a given amount of mass moving with respect to time. So many X mass units moving with a velocity. speed x direction.
You seem to want to equate molecules to mass, certainly, the molecules make up mass BUT big BUT, in fluid mechanics you can take the weight and convert it to mass, ie pounds to slugs, etc.

Ie if you have a stream of water or a gas coming out of a pipe say horizontal for the direction, and a speed of Y feet per second and it enters into a FIXED VANE, ( two types of Vanes, fixed or moving each with a different formula)
and the direction is changed, then this mass flow rate experiences a change in direction, which is a change in velocity, which is an acceleration which produces a force.
Merely hold your hand out the window when driving a vehicle and you can experience the force. You can, and rightfully so, say that as you move your hand from parallel to the flow to perpendicular to that you increase the amount of mass that
because the cross sectional area changes. BUT if you keep the area of the cross section the same, (you cannot do this with your hand) but change the outlet angle with respect to the inlet angle, which is zero for this example, the force increases
until you are perpendicular to the flow. (yes, the back side of the vane will experience a lower pressure but the significant force is the upwind side)

This is basic vane theory.

In summary, you only need to know the mass flow rate and the change of direction, of a fixed vane, to calculate the resultant lift force DUE TO THE UPWIND SIDE.

To calculate the upwind side force you need to know the mass flow rate that is impacted.
With a sail this is difficult if not impossible to determine as the sail shape makes it improbable to determine the value. BUT the effect of the change of direction of the mass flow rate produces the thrust

 

As mentioned in post 683, you more than likely cannot measure with a high degree of accuracy the total mass flow rate in a sail. The cross section changes and I suspect that the trailing edge is not the same throughout the
sails trailing edge.

 

Exactly, there is no need to think about molecules. Certainly, the molecules create the mass, no argument there. But the advance fluid courses, have never included a count of molecules or the speed of the molecules within a
volume when doing accurate calculations of fluid flow. I need to know the weight, or density, I need to calculate the mass, or mass flow rate, throw them into the equation and the finished values come out the other side.

 

SA You can't do that with a gas.
Why not, you know the average velocity, say in a pipe, you know the cross sectional area, and you determine the volume flow rate, calculate the mass of the flow rate, and hence you have a mass flow rate. Again,

Barry said: ↑
@ So the air above the wing provides a quasi containment boundary, mixing of course as it moves down the wing, creating and holding the faster moving low pressure air against the wing (with a resulting lower pressure)

SA, you dispute that this can happen. A meteorite with high density moving at speeds of 44 miles per second, 158,000 miles per hour can skip of the higher density atmosphere of earth.
Opening a nozzle of compressed air into a room, the higher velocity -lower pressure air will maintain its flow stream until it mixes, (creates turbulence,) absorbing energy, until you can not longer feel the effect of the jet.
By the way, it was you who said that you wanted to keep the wing out of the discussion, was it not?
Not keeping on the sail program, with a wing, the highest pressure area, the stagnation point provides a high pressure source that creates a high velocity - low pressure (Bernoulli) stream over the upper part of the wing until it mixes with the higher pressure air above the wing. Above, ie not close to the wings upper surface.

I do not subscribe that this happens with with a sail. It may be part of the lower than atmosphere pressure on the back side of the sail.

 

I wondered what you meant by "Mdot" in your earlier posts. Maybe it would have been prudent for me to examine that at the time, but I thought you were doing some sort of matrix operation on the acceleration vector.

But no, it seems you have invented a whole new mathematical syntax, where putting a dot over a variable identifying mass means mass moving with respect to time.
In calculus, a variable x with a dot over it usually refers to x as a distance variable and can mean the first differential of distance over time, otherwise known as speed.

Extending that syntax to your usage: an m with a dot over it would be the first differential of mass over time. No involvement of a mass moving, but perhaps a mass changing with time. Maybe atomic physics where atomic reactions convert mass into energy, but not something we are familiar with in classical mechanics.

 

The air passing over a sail (or a wing) is not contained in a pipe. We don't have a "cross-sectional area".
We don't have a quasi-containment boundary.
That's the problem.

 

I have not invented anything and wish that you would be more prudent in your comments. Below is NASA's explanation of it. Very BASIC fluids equation.

Mass Flow Rate https://www.grc.nasa.gov/www/BGH/mflow.html#:~:text=We%20can%20determine%20the%20value,rate%20from%20the%20flow%20conditions.&text=A%20units%20check%20gives%20area,density%20r%20times%20the%20volume.&text=To%20determine%20the%20mass%20flow,the%20mass%20by%20the%20time.

 

T O B E C L E A R, I have not commented about the air passing over the back side of a sail up to this point.

Hate to go back to the wing, If you have a very high pressure area and it is able to bleed into a low pressure area, the air in the high pressure area will exit this area at a high rate of speed. This is what I am saying occurs with
a wing N O T A S A I L. With a wing, the high pressure area feeding the upper part of the wing comes above the stagnation point.