4 Replies Latest reply on Jan 8, 2017 6:44 PM by Mark Keown

# Setting the right boundary conditions in mine Flow Simulation

Hello everyone,

In my last post I asked for help because I got some errors when running my Flow Simulation. Now I solved this, but I'm still struggling with setting the right boundary conditions for my Flow Simulation. Because I have simply no exact idea of the right boundary conditions.

The situation is as follows (see also the picture):

We have an empty fuel tank, which consists of two tank halves. So in real life there is only air in it. The fuel tank is filled through the filler neck with a constant volume flow. This is boundary condition one (hard to see in the upper left).

When running the simulation now, I got the error message from the last post. So I put on all inside surfaces a boundary condition with environmental pressure. The fuel cap is open at this time, so there is an ambient pressure in the fuel tank I guess. Am I right here?

When I run the simulation now, I don't see any decrease/increase of velocity or pressure when contacting the tank baffles and at the connection. (See pictures) Only at the filler pipe I see a decrease in velocity. Also is the velocity much lower at the beginning of the connection instead of mine calculated value. The surface plot of the pressure looks also really weird.

I'll hope anyone can help me with this simulation. I would like to simulate the influence of the fuel baffles on the filling of the fuel tank. My goals are to determine the pressure drop over the connection and the volume flows/velocities at the beginning and end of the connection hose.

• ###### Re: Setting the right boundary conditions in mine Flow Simulation

In Flow Simulation will not resolve the interface between two fluids - in this case air - fuel.

This is a static simulation so the tanks are show full with NO fluid movement.

This problem best solved with a spreadsheet not Flow Simulation.  Flow Sim may be used to determine losses in each section of the problem but book values may actually be better.

• ###### Re: Setting the right boundary conditions in mine Flow Simulation

Thanks for your response. That's clear.

Excuse me for my late response.

Meanwhile I've done some research and found that its possible with CFD software like Ansys or Abaqus. Unfortunately, this is not very easy.

How do you mean that with a spreadsheet? Can you give some literature of the books you mean.

• ###### Re: Setting the right boundary conditions in mine Flow Simulation

Just for reference this called a sloshing problem. It will be helpful to know in your searching.

• ###### Re: Setting the right boundary conditions in mine Flow Simulation

I am referring to hand calculation or or using excel.  Any fluids, fluid flow, pipe flow text book guide you on how to do this.