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Primitive variables in Fluid Mechanics

  1. Sep 17, 2005 #1
    Hello!
    I know that the primitive variables in fluid mechanics are velocity and pressure. But why?
    I don't see how "primitive" these variables are...What does it mean by a "primitive variable"? Is that all other variables in a fluid flow can be derived from velocity and pressure? Is there any other set of primitive variable? Lastly, how do you know velocity and pressure are primituve variables?
     
  2. jcsd
  3. Sep 18, 2005 #2
    can anyone kindly address this?
     
  4. Sep 19, 2005 #3
    I am not aware of such terminology but they are the main variables. You can manage any fluid flow problem if you know these two things.
     
  5. Sep 19, 2005 #4
    quark, thanks! I was afarid that no one is going to help me out. :frown:

    Why can we manage all flow problems if we know these 2 things?
     
  6. Sep 19, 2005 #5
    Try this ....
    When you try to solve a fluid feild without energy equation (heat transfer)? Conservation of mass and Conservation of momentum (Derived from Newton's Second law) are sufficient. You will find the main variables are pressure and velocity. With pressure and velocity information you can find the fluid feild. BESIDES all the properties.
     
  7. Apr 14, 2010 #6
    QUOTE=hanson;752113]Hello!
    I know that the primitive variables in fluid mechanics are velocity and pressure. But why?
    I don't see how "primitive" these variables are...What does it mean by a "primitive variable"? Is that all other variables in a fluid flow can be derived from velocity and pressure? Is there any other set of primitive variable? Lastly, how do you know velocity and pressure are primituve variables?[/QUOTE][/FONT][/SIZE]
     
  8. Apr 14, 2010 #7
    what is primitive variable? i know it is velocity and pressure,but why it is? Is that all other variables in a fluid flow can be derived from velocity and pressure?
     
  9. Apr 15, 2010 #8

    minger

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    It depends on what form the governing equations are written in, and how we interpret them.

    Typically, when we write the Navier-Stokes in strongly conservative form, they are in terms of the conserved variables. That is, mass, momentum and energy. However, one doesn't typically think of flows in terms of momentum and energy, we would prefer to use velocity and pressure. So, the primitive variables are mass, velocity and pressure.

    You are opposite in thinking that everything can be derived from velocity and pressure. It is in fact that everything can be derived from momentum and energy (with some other variables of course).
     
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