# significance of energy conservation laws

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 November 10, 2015, 18:55 significance of energy conservation laws #1 Senior Member   Join Date: Jun 2010 Posts: 111 Rep Power: 15 Am I correct in saying that: in some cases the energy equations is part of the governing equations of the flow (for example in the Euler equation or for an incompressible flow where temperature is important). Other cases, (for example, laminar isothermal incompressible flow) can be described without the energy equation. Does the second category, suffer from numerical instability because the energy equation is not being solved as part of the predictive process? In other words, energy may not have been conserved? Thank you.

November 10, 2015, 19:25
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Filippo Maria Denaro
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Quote:
 Originally Posted by Hooman Am I correct in saying that: in some cases the energy equations is part of the governing equations of the flow (for example in the Euler equation or for an incompressible flow where temperature is important). Other cases, (for example, laminar isothermal incompressible flow) can be described without the energy equation. Does the second category, suffer from numerical instability because the energy equation is not being solved as part of the predictive process? In other words, energy may not have been conserved? Thank you.

But the only energy form that obeys a conservation law is the total energy...other form of energies have a source term taking into account the conversion of a form into others

November 10, 2015, 19:46
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Quote:
 But the only energy form that obeys a conservation law is the total energy...other form of energies have a source term taking into account the conversion of a form into others

November 11, 2015, 06:04
#4
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Filippo Maria Denaro
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Quote:
 Originally Posted by Hooman Can you please be more clear? I don't understand your comment.

I mean that if you consider for example the kinetic energy equation, it is in conservative form only for the theoretical inviscid flow case....In general viscous cases, the source term is responsible of the transfer of kinetic energy in internal energy. Ony summing all the form of energies the sources term disappear.

 Tags energy balance, numerical methods, stability