2D CFD analysis of internal flows

2D CFD analysis

SimWorks cannot perform pure 2D CFD analysis, however it is possible to run a quasi-2D simulation using an extruded 3D geometry and a specific set of boundary conditions on the outer domain.

Moreover, it is possible to use an outer domain smaller than the geometry itself to define an internal flow analysis, like in the images below.

Setting up the 2D CFD analysis with an oversized geometry

In the following tutorial we will use our free CFD software SimWorks. Before starting this tutorial, we recommended to complete the base SimWorks tutorials and the SimWorks introduction as we will assume some familiarity with the software functionalities.

This is a simplified CFD model of an heat exchanger extruded in Y [1]. Only one half of the actual heat exchanger will be modelled and using a set of defined boundary conditions it will is possible to define a 2D simulation. Since the Y dimension of the heat exchanger is much bigger than the other two dimensions simulating, it in 3D would be computationally very expensive and as the flow in Y would be very uniform away from the borders, we can reduce the dimensionality with a quasi-2D approach:

Heat exchanger modelling [1]
3D view of the extruded CAD surfaces
2D CFD simulation pipes section
Section of the extrusion

The first step is to download SimWorks from the link below, which is completely free and unrestricted. You can follow the installation procedure described in our installation guide and you can also download the geometry file for this tutorial here.

Create a new simulation

Simply follow the steps of one of the base tutorials to define a new simulation, select the geometry tubes.igs, select mm as Geometry unit and import the geometry.

Define an outer domain with dimensions 200 100 320 in the position 50 0 130. The Point in mesh will be in the position 0 0 100.

As you can see the geometry is sticking out of the actual outer domain box, this is intentional as we want to define a quasi-2D simulation. The geometrical region outside the outer domain will be automatically disregarded by the mesher: 

Define the boundary conditions

Define the following boundary conditions on the 6 faces of the box:

  1. Symmetry on the mid plane → the CAD geometry is a section of half the heat exchanger so this constraint will reflect the geometry on this plane
  2. Symmetry on both the lateral faces → since this is a small section of the actual pipe we will define a symmetry condition on both the sides to define a 2D simulation
  3. Inlet velocity normal 5 m/s → inlet condition as in the reference image
  4. Non-slip wall → since the radiator is placed in a physical tube this side is an actual wall
  5. Pressure outlet 0 Pa → exit condition at the bottom of the radiator

Run mesh and simulation

We strongly reccomend starting the free 14-day trial of the commercial version of SimWorks (it is free without the requirement for payment information and it is possible to extend it further for free) to be able to run the simulation on multiple cores and with unlimited postprocessing capabilities.

Define a mesh base size of 10mm and leave all the othe parameters as default, as usual this is only to quickly run a tutorial in real life you would want to run a much finer mesh.

Define 4 cores (8 if you have 8 physical cores) in the Setup section and run the mesh, finally load it in the Fields viewer (as done in previous tutorials just right click on the completed mesh and select Fields and then Load):

Mesh visualisation of the 3D part and a plane normal to Y

Run the simulation and visualise the results in the Fields viewer. As you can see from the 3D view the pressure field (p with ranges from -50Pa to +80Pa) is constant along Y meaning that we successfully simulated a 2D flow:

Now purely looking at he Y plane it is possible to see the flow separation at the top of the radiator corresponding to the top roof with a clear loss of flow velocity and a corresponding loss of pressure:

Try the free version of SimWorks or contact us to find out more