If you were to take an elevator to the top of a building; and your friend took the stair and you both jumped who has the greater PE? as you see it doesn't matter the path [such functions were the path determines the amount of something are called 'path functions'....but any function that only depends on the initial and final states--and can be completely characterized by the initiall and final state are called state functions---like the bottom and top of that imaginary building----state functions are always written as 'delta somthing'
delta[E[internal enery],H[enthalpy,S [entropy]---but heat and work are path functions as a result of the PE available in the molecules of air as they are heated with compression---can be specified anyway---in others words---- you can assume an isothermal compression or an adiabatic compression, both different types of work and/or heat, but since the final quantities are equal---the work done to cause compression of the atmosphere on the airfoil..can be written by either equation [the one for isothermal or adiabatic] ---so lets look at those relations between the state functions and path functions--I need to do some light algebra--for this
---and when I write d= I do not mean differentials--- I mean delta--final minus initial---
E is the internal energy of a gas[atmosphere] if you add to that the work of expansion/compression [PV work]--you get the Enthalpy [H] of the gas
So
dH= dE+PV work ---if I subtract the wasted energy that is used to create disorder--entropy dS-- [which increases with temp]--
I have my Free energy ----dG
So I finally am left with dG = [E+pv work ==dH]----dG = dH - TdS---
there's
--more but I'll leave this to digest--so I can really be understood--I'll get to the point--- but I want to make sure I'm being understandable===and I wouldn't go too far ahead of me unless you're an engineer or scientist--because it may be hard to guess where I'm going---but it takes along time for me to get Tired
any questions so far?
I'll get to how it causes buffeting and all the good stuff--which is all to do with this ---but it's not an easy path for a non-specialist and it's hard to write math on Pprune and explain nice, but I'm not trying to be confusing--that's not hard to do for a few of us here if that's the goal
PA