simple potential flow question
 

Hi,

I've written a 3D, transient finite element model for the Laplace equation to simulate potential flow.

To validate this model, I'm trying to propagate a 'pulse' of pressure from one end of a confined duct to the other end. In the first time step, I prescribe a boundary potential at one end of the duct. I then release the boundary for subsequent time steps. I would expect a pressure pulse, or wave-like phenomenah, to then continue along the duct. Instead, I'm observing an initial potential at that boundary and adjacent nodes that simply dissipates with time.

Could a pressure pluse, or wave, be modeled with the Laplace equation at all? Or have I incorrectly prescribed the boundary conditions, or made an error in the code itself?

Any help would be appreciated...

-CS

Re: simple potential flow question
 

I'm not sure I understand what you are trying to do (you need to give more details of the boundary conditions)

However, for potential flow the solution at every point within the domain is completely determined by the conditions on the boundary. This means that waves effectively travel at an infinite velocity. Furthermore, since time does not enter the potential flow equations explicitly, there is no need to time march the problem.

Hope this helps,

Tom.

Re: simple potential flow question
 

Laplace/Poisson equations do not have any wave-like solutions. The unsteady compressible potential flow equations do have wave-like solutions.