Radiation in Flow Simulation – Part 2: Refraction
In my earlier blog on Radiation in Flow Simulation, I showed
how Flow accurately ‘ray traces’ solar radiation and how surfaces can be set as
‘Symmetry’ Radiative Surfaces that perfectly reflect the radiation. I used a
parabolic solar trough to illustrate this.
That work led me to wonder whether Flow could refract
solar radiation through a transparent medium. Could it bend the radiation
waves? If so, Flow can be used for all manner of radiation / heating / lighting
I decided to test a magnifying
glass and see if a convex lens would concentrate the sun’s solar radiation
at a spot – like I used to do when a boy, setting fire to newspaper. If so, it
would prove that the ray tracing bends the light as it passes through the
Here is my magnifying glass.
I have positioned it above a wooden
surface and applied a transparent appearance to the lens body. The lens has a
radius of 150 mm and I have positioned it such that the wooden floor is exactly
150 beneath the centre of the lens – i.e. at the focal point.
The set up in Flow is an External study with Solar
Radiation and Gravity enabled. I
used the ‘Direction and Intensity’ option for defining the solar values
and, for convenience, set the sun to shine straight down the Y axis. The
‘Gravity’ option enables natural convection which will cool the surfaces by
drawing in cold air as warm air rises from an expected hot spot.
There are some further Radiation options you can enable in the ‘Calculation Control Options’.
Below you can see that I have set the ‘Solar ray tracing’ to ‘Forward’ meaning
the rays start at the sun and are traced through the lens to the floor surface.
You can also define the ‘Number of rays’ and the ‘View factor resolution
level’. These will give more refined rays but take longer to run. I used the
The results show a hot spot at the focal point. The surface
of the wood has reached 368 degrees C.
The animation below shows how the hot spot creates a
vertical current of warm air which in turn draws in cool air.
Refraction through Magnifying Glass
Flow is not a specialist Optics package so I would not
expect it to be used for advanced optical designs like car headlights. If you
want that capability, there are SOLIDWORKS partner products that can be used.
To see these, go to … http://www.SOLIDWORKS.com/sw/products/search/results.htm
… and search for ‘Optics’. There are no less than 8 specialist
tools for Optics.
However, for thermal studies where radiation reflects or
refracts solar or other radiation, Flow is an exceptional, easy-to-use tool
that gives accurate real-life results.
By Andy Fulcher