Account for all the small changes carefully. Then the system, however large, is not so difficult to predict
Fly with Magnar: Why are so many pilots wrong about Bernoulli’s Principle? at https://www.youtube.com/watch?v=uyRx25MSWng
@woodpile66 Most folks here seem to say that low pressure exists because the flow speeds up, but that group does not account for why the flow sped up in the first place, or the mandatory physics. I offer that the wing has acted on a fluid and accelerated it. The bottom by blunt force change in direction, the top by leveraging coanda effect. Velocity being preferable, as it is squared in the lift equation (the bottom does not share this advantage). This is a force which has to be accounted for with an equal and opposite force. Some say this only happens on the bottom, but the physics don’t change. Once the air has been accelerated, a vacuum has formed (larger and smoother replacement flows result from more efficient acceleration). Bernoulli’s EQUATION (not a force) is a great way to measure how efficiently the foil accelerates (speed and direction) air by measuring the decrease in static pressure. The group that feels the wing sucks itself up in the air is probably standing in a bucket and lifting themselves by the handle. I would hope someone can explain what happens to the wing when it causes air to accelerate. Furthermore, while they are thinking about it, what if you replaced a single engine prop with a rocket motor? Everyone would measure the force by the mass and speed of the ejected matter – but when it is a propellor, most people claim it is an airfoil and suddenly we measure the vacuum out front. No one ever puts Volkswagens in front of a 747 to watch them flip over. Sure, the engines suck in air, but what matters is when huge energy gets added to the flow – not the vacuum. Does water form a vacuum over a diving plane?
My Comment: You might want to look up “pressure gradient forces” and “impulse” of fuels. The pressure increases with fluid velocity at constant density. At higher pressures the density can increase giving more pressure. Rules of thumb memorized to model invisible flows are less useful than modeling every voxel individually with all that is known about the flows, fluid properties, heat, temperature, energy, three axis velocities and acceleration. Ultimately those models all have to be simple accounting, because the digital models are calculating with add subtract multiply divide mostly.
Look at adjacent cubic voxels in a simulation and then check the equations for momentum, energy, pressure, velocity, and all the other things. It is an accounting model. Ways of estimating might change, but it is not complicated taken a tiny piece at a time. Magnetic fields, lasers, microwaves, mm waves, THz, UV, soft x-ray, acoustics, plasma jets, ionization, electric fields, ion and electron and nano-particle beams – there are many ways to image and modify turbulence, temperature, velocity profiles. And there are many ways to look ahead and plan for the air that will be encounters. The speed of light is thousands of times faster then the aircraft and air. And the air has a finite (albeit large) range of states and changes. The computers now can image, process, predict, verify and change in real time, and with electric and electromagnetic field, some things not possible with mechanical, hydraulic, motor and solid parts, similar to what the Wright brothers used in form and presumptions.
You might want to look up “plasmonics” for electromagnetic and field methods near surfaces. Many tools are available off the shelf now (COTS – “commercial off the shelf”).
James Melcher wrote ‘Field Coupled Surface Waves (MIT 1963). The full title is Field Coupled Surface Waves – A Comparative Study of Surface Coupled ElectroHydroDynamics and MagnetoHydroDynamic Systems. His methods are out of date now, but the ideas are that old. Only in the last few years are sensors, computers, memories and algorithms fast enough to apply those and subsequent methods in real time. Flying fighter jets with rigid surfaces pales in comparison with flying with boundary surfaces that can have energy densities hundreds of thousands of times the ambient air or more. You can reach out ahead of the vehicle and change the air and its fields remotely.
If you ever wondered how to stop a vehicle on a dime or make it hover without jets or in near vacuum, there are tools for that kind of design and have been for decades, if you could afford the parts back then or now.
Filed as (Account for all the small changes carefully. Then the system, however large, is not so difficult to predict)
Richard Collins, The Internet Foundation
