[Big Kahuna]

I am trying to simulate a Hagen Poiseuille flow inside a tube (a pipe). I obtained all my codes from http://files.the-foam-house5.webnode...pter4_Pipe.pdf. The person who wrote the codes had a single pipe through which fluid flows. What I am trying to do is to attach a second pipe (with a smaller diameter) to the the tail end of the first pipe and watch the fluid flow from the first pipe into the second pipe, and since the second pipe is narrower, I was hoping to see fluid velocity increase as it enters the second pipe. What I did was modify this guy's blockMesh code to reflect the fact that there are now two pipes, not just one. But when I ran the simulation, the fluid filled both pipes at the same time! It wasn't a flow from pipe 1 into pipe 2 -- it was a simultaneous inflow of fluid into both pipes. Is this because I did not create a "hole" at the tail end of pipe 1 and a "hole" at the front end of pipe 2? Is this absence of "holes" in the pipes that is causing the program to think that the two pipes are distinct objects rather than one continuous object? I don't know how to create "holes" in pipe 1 and pipe 2. All I want to do is see fluid flow from pipe 1 into pipe 2 and the fluid velocity increase as it enters the narrower pipe. Any advice, please?

[piu58]

> the fluid filled both pipes at the same time!

I don't know your case, but the normal, straightforward simulations are such that the pipe(s) are always filled with fluid. The simulation only starts the flow. It is quite normal then, that you get a fluid velocity everywhere immediately.

he case you described need a two phase simulation, which is more complicated.