User talk:David Weyburne/sandbox

New theory of lift

Thank you for taking an interest in this area of Wikipedia. I see three of the four sources you are proposing to cite are publications written by yourself. This is potentially a serious problem. Before going much further please familiarise yourself with the guidance available at WP:SELFPUB and WP:ABOUTSELF. Dolphin (t) 14:17, 17 September 2022 (UTC)

In this edit I wrote “Some of your sentences are statements of the obvious and therefore unnecessary in your description; and others are either incorrect or misleading.” I will give some examples of what I had in mind. The following sentences are generally true in the field of fluid dynamics but they contribute nothing to a new explanation of lift. They lack substance in relation to your new explanation of lift.

The equations that govern airflow around an airfoil require the mass, momentum, and energy be conserved. An important feature of these equations is that they only become important where the velocity and pressure are changing. The mass of the free stream air approaching an airfoil surface is conserved by being redirected around the airfoil. This mass diversion causes the air velocity and direction to change as the incoming airflow approaches the airfoil surface. Changes in the air's velocity means that the momentum (equal to the mass times the velocity) is also changing.

Another example:

Aerodynamic lift is calculated as the pressure difference above and below the airfoil surfaces times the airfoil’s surface area. This pressure difference, in this case, is caused by the airfoil being slightly tilted to the incoming airflow. The overall aerodynamic lift force for the airfoil with a slight tilt to the incoming flow is positive but it is zero for the untilted symmetrical airfoil case (not unlike the effect obtained by sticking your hand out the window of a moving car).

The following sentence is either incorrect or misleading.

The momentum conservation equations require that the diverted incoming stream-wise momentum must be: 1) partially converted into perpendicular-to-the-flow momentum (airflow up or down)

In the above sentence you appear to be suggesting that the incoming stream, which is flowing in the horizontal direction, is deflected to be perpendicular to the horizontal direction (either up or down) and that this is conservation of momentum!

Talking about momentum conservation, you write, in para (2):

2) partially into pressure changes at locations where the velocity changes take place. This requirement provides the critical connection between the velocity and pressure in the near airfoil region.

Changes in speed and pressure within a fluid are related by Bernoulli’s principle which is based on conservation of energy, not conservation of momentum. If you wish to relate speed and pressure by conservation of momentum you need to explain it very carefully indeed because it is a radical idea. You cannot simply state it as fact and hope that discerning readers will swallow it.

Another example of a sentence that is incorrect or misleading is this one:

To understand how this conservation requirement creates aerodynamic lift, we need to know the shape of the boundary layer around the airfoil.

In the above sentence you are suggesting that aerodynamic lift is created by a conservation requirement! This is not credible in any writing that purports to be based on modern scientific principles. Dolphin (t) 05:59, 18 September 2022 (UTC)

Sorry, I initially missed your comments in my sandbox. I appreciate your detailed comments. My reply to the comments about being unnecessary: The fact that the flow governing equations are only operational when the velocities and pressure are changing is the basis of the lift argument. It may be obvious to the expert but not to to the non-expert. When one views the velocity profile plot in my explanation, it is the fact that the velocity is constantly changing in the near airfoil region that is important to notice. The second unnecessary comment you made is met for the non-expert. As to the incorrect statements: The momentum in the flow direction reference is exactly true for the Prandtl momentum equations and is a very good approximation for the full equation under most flow conditions. The key is that I said partially converted. I stand by the statement. As to your comment about speed and pressure being related to the Bernoulli’s principle which is due to conservation of energy is itself an incorrect statement. Presently, our theoretical understanding of Fluid flow is that it is well represented by the the mass, momentum, and energy conservation equations along with an equation of state. To state that the pressure field is being controlled by the just the energy equation is incorrect. My use of the momentum equation was to present a simplified explanation of how the velocity changes must result in pressure changes. I could of have made an energy equation argument but that would require a much more detailed argument that does not meet the simplified explanation requirement. Finally, as to the created comment: The conservation equations are the theoretical basis of our understanding of fluid flow. That aerodynamic lift is predicted by the conservation equations is well established in numerous CFD simulations. I am not sure what is not credible about this fact. David Weyburne (talk) 12:33, 22 September 2022 (UTC)

I challenged your use of the word "creates" in relation to aerodynamic lift. We seem to be in agreement because in your edit above you have written "conservation equations are the theoretical basis of our understanding of fluid flow", thereby avoiding use of the word in question, "creates". Similarly you have written "aerodynamic lift is predicted by the conservation equations", again avoiding use of the word "creates". I agree that conservation is usually the theoretical basis of our understanding of things; and that we can predict things using conservation equations. Perhaps we can agree that saying "this conservation requirement creates aerodynamic lift" is an oversimplification that doesn't deserve a place in an encyclopaedia? Dolphin (t) 13:26, 22 September 2022 (UTC)