Radiator Modelling: A Guide to CAD Creation

Modelling radiators ready for CFD in bramble requires both accurate modelling and precise naming. This guide covers how to prepare your radiator CAD and configure it within bramble’s Template Cases.

bramble models radiators using porous media. This approach accurately simulates airflow characteristics, as the porosity of this media gives the same air-side pressure loss versus velocity as the real radiator will.

Naming conventions are crucial when setting up your radiator in the Template Case form (as seen below). You must use the name you assign to your radiator in the zone names of your uploaded parts. For example, if you name your radiator “oil-rad-rhs” in the form, you’ll need to name the uploaded front face “toint-oil-rad-rhs” to maintain proper connections. Following this simple rule ensures your radiator model functions correctly within the simulation.

Modelling Radiators - template case form

Modelling radiators in CAD

The recommended best practice for modelling radiators in bramble involves splitting it into three main components:

The frame
The upstream front face
The downstream back face

Radiator in CAD, split into frame, upstream and downstream face

Internal walls of radiator CAD - modelling radiators

Modelling radiators in CAD – frame

The model radiator frame must be a solid, watertight piece of geometry to prevent any flow or CFD mesh from leaking into it. Keep in mind that the frame includes internal walls.

Name the frame’s zone using the radiator’s name and its location on the vehicle. The typical format follows:

For example:

body-rad-water-lhs or eb-rad-main

If the radiator appears on both the left and right sides of the vehicle, include lhs (left-hand side) or rhs (right-hand side) in its name.

Modelling radiators in CAD

– front and back faces (toints)

You should represent the front and back faces of the model radiators as thin surfaces covering the entire face of the core. These faces should seal perfectly to the radiator frame ensuring no leak paths from inside the core to the outside.

Extrude these faces slightly into the frame by a few millimetres to oversize them; this adjustment helps them seal to the frame when you convert the model into an STL file.

To maintain consistency, name these faces using the format:

toint-<radiator name>-<up or down>

For example:

toint-rad-water-lhs-up and toint-rad-water-lhs-down

Apply –up and –down to the upstream and downstream faces, respectively.

Upstream and downstream face for modelling radiators for CFD

Radiators in the template case

Name – The name given to the radiator. Should be alphanumeric, no spaces or special characters other than _ or -.

Inside Point – The inside point tells bramble where in space the radiator appears in the model. It should be the x, y, z-coordinate of the centre point of the core in metres.

Different values of porosity can be applied in different directions through a radiator. This is typically used to represent fin alignment with high porosities being used to stop flow travelling up or across the radiator face. So, we need to tell bramble the alignment of these ‘fins’ using the through and orthogonal vectors.

Through Vector – The unit vector normal to the radiator’s front face, pointing in the flow direction.

Orthogonal Vector – The unit vector pointing across the radiators front face, typically right to left. As its name suggests, it should be orthogonal to the through vector. This means using sufficient decimal places should be used when entering the vector into the template case. Three or four should suffice.

Darcey-Forchhiemer Coefficients

The air-side pressure loss through the core is modelled using a Darcy-Forchhiemer approach to predict the momentum and viscous losses as the air travels through the radiator. To apply this method, you must set both the Darcy and Forchheimer coefficients in the template case. If you already know these values, simply enter them directly into the form. Otherwise, you will need the air-side versus pressure loss curve and to use bramble’s calculator to determine the values.

Press the ‘cog’ symbol next to either of the coefficients to open the calculator.

Add the velocity vs pressure loss data to the ‘Pressure Data’ form and details of the radiator into the Porous Property table.

Thickness refers to the core’s depth in the ‘through vector’ direction.

Set Viscosity and Density to the air property values from the experimental test that produced the air-side pressure loss data.

Radiators in the template case

Factors – This setting is used to control the porosity in the three directions of the radiator’s coordinate system. The first factor, for the through direction, will typically be 1 (pressure loss equal to that of the Darcy-Forchheimer calculation). The other two directions (the orthogonal vector and its cross product with the through vector) will typically be set to 10 (10 times the D-F calculated value). This will sufficiently restrict the flow from moving in these directions without destabilising the CFD solution.

Up/Down – Should be set to on and tells bramble there are two surfaces representing the up/down faces of the core.

Export Slices – Can be toggled on to make bramble export a slice through the radiator core after the simulation completes for generating post-processing images. By default, this slice will have variables of Cp, CpT and Normal Velocity but additional variables can be specified using the ‘Slice Fields’ option.