Incompressible Potential Flow with COMSOL Version 6.2

COMSOL continues to make updates to Version 6.2, and in this month’s tips and tricks video, we are going to demonstrate how you can use the new update for Incompressible Potential Flow, which can be used to replace Laplace’s Equation to initialize fluid flow equations.

Click below to watch as I walk you through the process. To help you follow along, we have included the video transcription below.

There’s no reason to learn software programs through trial and error, so in addition to our tips and tricks, our upcoming training classes will support you, the COMSOL user, in utilizing best practices with many of the COMSOL modules. Please visit our training calendar and find the course that is best for you.

Incompressible Potential Flow with COMSOL Version 6.2 Transcription

Today I’m going to show how to use a new 6.2 update for Incompressible Potential Flow. This can be used to replace Laplace’s Equation in order to initialize fluid flow equations, such as large eddy simulations or turbulent fluid flow models. You could still use Laplace’s Equation, which is really useful because you do need the CFD module in order to use Incompressible Potential Flow. So, let’s get to it.

So in order to use Laplace’s Equation you have to add the module or add interface and change the custom units of dependent variable to meters squared per second and the source term to one over second. It’s super helpful to also change the dependent variable to phi so it does look like your incompressible potential flow interface and what you usually do when you’re doing these types of problems. So if you look at Laplace’s Equation 1 and you look at the Incompressible Potential Flow you could see that the equations match up perfectly.

The next one we’re gonna look at and see how things matchup is go to Zero Flux 1 and look at the Wall 1. And you could see that these equations match up perfectly as well. So now we’re seeing how the incompressible potential flow can completely replace Laplace’s Equation. Now we look at the Flux/Source 1, which you do have to add and the Velocity 1 term, which you do have to add, and these match up perfectly as well.

Finally, you have Open Boundary 1, which matches with Dirichlet Boundary Condition 1. Now in order to get either Laplace’s Equation or Incompressible Potential Flow to be your initial conditions for your turbulent fluid flow, you have to add an Initial Values 2 to your turbulent fluid flow models either in Laplace’s case or your potential fluid flow case and put your negative gradient into the Velocity field for the Laplace’s case or take your ipf.u, ipf.v, ipf.w, which is the velocity outputs there in incompressible potential flow as your inputs to the turbulent fluid flow. Now in order to run your studies correctly you need two study steps. Your first study step, each of them is either going to be your Laplace’s Equation or your Incompressible Potential Flow step. And your second step is gonna be that Turbulent Fluid Flow step. Finally, once you run it you can look at your velocities, which is a little bit simpler in the incompressible potential fluid flow step because it immediately gives you a velocity from the potential flow solution. Whereas in the Laplace’s case you have to create yourself a slice plot of the gradients in the z direction, and the streamline is going to be the negative gradients. Whereas your streamline’s a lot simpler it’s just those velocity inputs or the outputs from the potential flow. And then you can just get your velocities from the turbulent model.

And there you have it that’s how you use either Laplace’s Equation or your new module, excuse me your interface, from the turbulent fluid flow model, which is the new update to version 6.2. It hopefully is a little bit simpler if you have that CFD module. There you go.