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Is air a viscous fluid or an ideal gas?

  1. Sep 2, 2011 #1
    A Newtonian fluid is a continuous medium with viscosity and can "stick to itself".
    An ideal gas is a collection of non interacting point particles.
    Obviously at equilibrium, air can be treated as an ideal gas, while dynamically it is treated as a Newtonian fluid. But it cannot be both (since these models are polar opposites). It must be something in between.

    Does anyone know of any good papers that explore this subject or give some insight into this matter?
    My intention is that I want to know if there is a different model, in essence a hybrid of the two, which can be applied to certain situations (I'm thinking of combustion/detonation or other non-equilibrium, high velocity processes).

    Thanks for helping.
  2. jcsd
  3. Sep 3, 2011 #2


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    Well considering that an ideal gas does not truly exist and is more of a concept used to simplify problems, it doesn't have to be "something in between" at all. Air is a viscous fluid. Thermodynamically, it can be treated as an idea gas most of the time in aerodynamics and for rough estimates it can often be treated as an ideal gas in a fluid dynamic sense as well (see potential flow theory). However, in reality, it is just like any other non-rarefied fluid not hovering around 0 K... it is a viscous fluid.
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