Learning Forum

[eric1234598765]

Hi,

I have a basic question to the energy equation defined in user guide in chapter 7.2.3

Here's energy equation:

[aitor.amatriain]

"Obviously, there's advection term on the LHS , or the divergence of pressure I've mentioned above, and that's what I expect to see in (7-23)"
There is also an advection term in equation (7.23). Why there should be a pressure gradient term in that equation?
None of the variants of the energy equation (internal energy, enthalpy, total energy) has a pressure gradient term.

[eric1234598765]

Hi, Aitor
Thanks for the answer According to 7-14, there's pressure gradient at the LHS which is wrote with the the energy.
Here's another example of energy equation from https://www.grc.nasa.gov/www/k-12/airplane/nseqs.html
and the red square in the picture is what I'm confused about.

Best Eric

[aitor.amatriain]

Yes, you are right, sorry (I guess you are talking about one of the two components of the convective term).
The enthalpy equation does not have a pressure gradient term. In order to see that, you can take the (total) energy equation as a starting point, and then applying the definition h = E - e - p/rho - v^2/2 you will get an equation without a pressure gradient term (e is referred to the internal energy)