Converting Navier-Stokes Equations to Lagrangian Frame of Reference

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SUMMARY

The discussion focuses on converting the Navier-Stokes equations from the Eulerian frame to the Lagrangian frame of reference, emphasizing the need to utilize total derivatives. The key distinction is that the Eulerian frame maintains a fixed control volume, while the Lagrangian frame moves with the fluid flow. The transformation involves changing the right-hand side of the equations to reflect time dependence rather than spatial dependence, specifically using the expression ρ\frac{D\vec{V}}{Dt} instead of ρ\frac{\partial \vec{V}}{\partial t}. Understanding total derivatives is essential for this conversion.

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  • Understanding of Navier-Stokes equations
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Homework Statement


I am asked to write down the momentum (navier-stokes equations) equations in the Lagrangian coordinate system. Gravity and viscosity can be ignored.

Homework Equations


[PLAIN]http://img443.imageshack.us/img443/974/65019601.jpg (Eulerian Frame)

The Attempt at a Solution


Am I correct in thinking that I only need to change the RHS to change with time instead of position? The RHS only contains p, so can I split this up into px, py, pz? I can't seem to find any relevant information anywhere.
 
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No, the fundamental difference between Eulerian and Lagrangian frames of reference (not coordinate systems) is that with Eulerian, the control volume is fixed in space, whereas Lagrangian moves with the flow.

The effect this has on the equations is that you end up with total (also called substantial) derivatives in the Lagrangian frame of reference. You'll end with something like:
[tex] \rho\frac{D\vec{V}}{Dt}[/tex]
Rather than
[tex] \rho\frac{\partial \vec{V}}{\partial t}[/tex]

You need to understand what a total derivative is to convert what you have into the Lagrangian form. If you need more help, let me know.
 

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