Greetings all.
I am working to solve a standard fluid flow problem (e.g. flow in a pipe as a start) using the General Form PDE interfaces instead of the Fluid Flow built in GUI. I am able to define a u-momentum and a v-momentum equation without too much difficulty, but it is the continuity equation that I am struggling with. Right now I have 3 instances of PDE General Form (2 momentum equations + 1 continuity equation). For the continuity equation, all of the coefficients are set to zero with the exception of the source, f. The source f is set equal to -(ux + vy), giving the spatial derivatives of the velocity components equal to zero (incompressible, Newtonian fluid). The problem now becomes the boundary conditions - the continuity equation must be satisfied everywhere (not just on the boundaries) in the domain! I can set all the boundaries to zero and it works fine, but I don't get a converged velocity field because there is no enforcement of continuity.
Does anyone have any insight on how the built in Fluid Flow module implements the continuity constraint? Perhaps I could use a probe to integrate "abs(ux+vy)" over the domain, but then I have no way of requiring that to be zero (or some small number).
Any advice would be greatly appreciated! Thanks!
I am working to solve a standard fluid flow problem (e.g. flow in a pipe as a start) using the General Form PDE interfaces instead of the Fluid Flow built in GUI. I am able to define a u-momentum and a v-momentum equation without too much difficulty, but it is the continuity equation that I am struggling with. Right now I have 3 instances of PDE General Form (2 momentum equations + 1 continuity equation). For the continuity equation, all of the coefficients are set to zero with the exception of the source, f. The source f is set equal to -(ux + vy), giving the spatial derivatives of the velocity components equal to zero (incompressible, Newtonian fluid). The problem now becomes the boundary conditions - the continuity equation must be satisfied everywhere (not just on the boundaries) in the domain! I can set all the boundaries to zero and it works fine, but I don't get a converged velocity field because there is no enforcement of continuity.
Does anyone have any insight on how the built in Fluid Flow module implements the continuity constraint? Perhaps I could use a probe to integrate "abs(ux+vy)" over the domain, but then I have no way of requiring that to be zero (or some small number).
Any advice would be greatly appreciated! Thanks!
