0
$\begingroup$

Reading materials online, I observe some explanation based on Bernoulli's principle, quoting the difference of air pressure above/below and difference of speed of airflow. While some say's Bernoulli's principle works only in special conditions (laminar, non-viscous, non-compressible, streamline, etc.) and the correct working is based on Newton's third law whereby, the airfoil pushes the stream downward and experiences lift upwards.

Bernouli's principle is also said to not work for symmetrical aerofoils and inverted aerofoil.

What is the final verdict of what causes lift?

$\endgroup$
  • $\begingroup$ Could you share your sources for the statements that Bernouli's principle only works in special conditions? $\endgroup$ – GdD May 20 '20 at 7:31
  • $\begingroup$ @GdD - khanacademy.org/science/physics/fluids/fluid-dynamics/a/… It is pretty standard thing that bernouli's principle is valid only for streamline, non-turbulent, non-viscous, incompressible flows. $\endgroup$ – Raj Arjit May 20 '20 at 7:58
  • 1
    $\begingroup$ @RajArjit, actually, Bernoulli's equation is just formulation of conservation of energy for adiabatic fluid flows, and often given for incompressible flows only (then you don't need to add the equation for adiabatic compression), and as such is always valid. $\endgroup$ – Jan Hudec May 20 '20 at 8:26
  • 1
    $\begingroup$ … of course with turbulent flow you have to take the $v$ in the Bernoulli's equation to mean the average magnitude of velocity of the particles, which is higher than their average forward velocity. But that does not make Bernoulli's equation invalid, just more complicated. $\endgroup$ – Jan Hudec May 20 '20 at 8:52
2
$\begingroup$

I think it is erroneous to say that lift is solely produced just because of the Bernoulli's or Newton's law.

Sixty Symbols(A youtube channel) explains the best how a wing actually produces lift.

Instead of explaining I thought this video might help you more than my explanation. And also look at "Incorrect Lift theory" by NASA

$\endgroup$
  • $\begingroup$ The discussion of the isobars close together at the leading edge contributing to the "acceleration of air over the top" reminded me a bit of a jet engine. The thrust indirectly is the energy source, as the movement creates this zone of increased pressure ahead of the wing. This adds to the decreased pressure behind the wing. Air moves from high to low. Wings work best when they have a slightly positive AOA (even when inverted!). Sorry this was labelled "duplicate", as it adds to the understanding of a very important fundamental subject. +1. $\endgroup$ – Robert DiGiovanni May 20 '20 at 13:38

Not the answer you're looking for? Browse other questions tagged or ask your own question.