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– the easy solution to running your own domain, website or online store today. Most of the research and development that
goes into sculpting and refining the aerodynamic shapes of the various parts of F1 cars is
made in the wind tunnel and in sophisticated computer models called computational flow
dynamics or CFD models. Make no mistake, this is where the majority
of the hard work that goes into designing and testing aero parts like wings and diffusers
takes place. But when the car hits the track there’s
a big opportunity for some final aero checking and verification. One of the ways teams can
do this is with the use of flow visualisation paint, or Flow Viz.
You’ve probably seen Flow Vis paint used on the cars in practice or testing sessions.
The most eye catching use recently was when Williams absolutely covered their car in various
colour blocks of Flow Viz to try and solve some of the mysteries of their misbehaving
chassis. More typically, though, Flow Viz is seen used
sparingly, precisely and in specific areas of the cars. You might see it on the front
wing, over diffusers, bargeboards, etc. So what is Flow Viz paint? How does it work?
And how does it help engineers and analysts understand their cars better?
The main idea of Flow Viz paint is to show the airflow patterns that manifest along the
bodywork of the car as it drives at speed. These flows are normally invisible because…
well, have you seen air lately? Exactly. No, you haven’t.
Flow Viz is a pretty simple product. It’s just a powdered dye suspended in paraffin
or kerosene or a similarly light oil. By suspended, I mean the dye sits happily in amongst the
oil once stirred but will eventually sink and separate from the oil with time. The oil
is just a medium to keep the dye flowing and free.
The useful thing about this mixture is that it doesn’t dry particularly quickly when
it’s all globbed together so you can splosh it liberally over the areas you want and the
paint will continue to run and flow as you drive the car at speed through the air.
A lot of normal paints would dry or stick around the areas you painted them and not
do anything particularly useful. The flow of the air around the car as it drives
will push the oil – and therefore the dye – along the surface of the bodywork all free
and flowing. But paraffin evaporates fairly readily and this will leave the dye behind,
stuck to the bodywork in all the flowing shapes its made in the airflow.
The aerodynamicists can then take photos of the car once it’s parked back up in the
garage and check to see if the paint patterns show the results they’d been expecting.
You’ll often see very brightly coloured dyes that stick out against the bodywork so
they can be easily seen when photographed by the team. But the dye itself may also be
fluorescent, meaning it will show up much more strongly under UV lighting. So if you
see Flow Viz that seems a little faint and unclear, the chances are the paint will look
a LOT more striking back in the garage under the right lights.
Now – importantly – the point of Floz Viz paint isn’t really to gain much quantifiable
or precise data about the aerodynamics. Instead, it’s a fairly quick and dirty method to
double check that the computer models and wind tunnel tests corroborate with real-life
running. Teams still can’t fully replicate the many
eccentricities of the real world from inside their own HQs (though Lord knows they try),
so a full scale run on a real track is the final, definitive test for that new front
wing or whatever that they’ve been developing behind the scenes.
Did it behave as expected? Does it differ from the old spec front wing in the way they
intended? Or is it giving some strange flow behaviour that you need to analyse and double-check?
This is the benefit of flow viz in the real world, though it has of course been used in
wind tunnels for many, many years – way before it showed its head in testing and practice.
Now, there may be extreme cases, like Williams this years, where teams just want to evaluate
the whole package and record lines over the whole chassis. You can do that, if you want,
but you really shouldn’t ever be at that point with a car halfway through a season.
OK, so you’ve slapped a load of flow viz paint on the part of the car you want to evaluate.
Your driver has done a lap or two and brought the car back to the garage.
How do you interpret the colourful mess left all over the carbon fibre?
Well, firstly – as outsiders, we’re never sure exactly what the aerodynamicists are
looking for in any given tests, particularly when testing one part against another. They
may be looking for any number of characteristics so we can’t speak to the result of any particular
evaluation. That being said, here’s what happens to
Flow Viz paint under various, important circumstances. Firstly, we can see clearly if there is a
strong, clean, smooth air flow along the bodywork, as opposed to a dirty and turbulent flow.
Just using a wing profile here as an example (as it’s easy to visualise): smooth air
flow will run nicely along the surface in good, coherent lines all running together
from beginning to end. You’ll see this in the Flow Viz pattern
too. Smooth, coherent lines just like someone took a nice, quality paintbrush and drew a
clean stroke across the bodywork. Satisfying to look at.
Smooth airflow is desirable because it’s predictable and stick to surfaces. It also
continues to be easily manipulated by further aero devices downstream as long as it continues
to stay coherent and flowing. Turbulent airflow is where the air gets chaotic
and starts to misbehave in twists and curls and acting in an unpredictable, blustery way.
This is often undesirable, particularly along the bodywork, which is where Flow Viz makes
its measurements. Turbulent flow will throw the paint into chaotic
splotches. You may see pools of paint gathering together in seemingly random patterns, distorted
waves of colour and other messy patterns. Just generally, paint gathering in anything
but those nice smooth lines we just saw is an influence of turbulence.
Another thing to look for is where the air flow is attached to and detached from the
bodywork. For the most part aerodynamicists design the
shapes of wings and other body parts (particularly aero devices) to keep the air flow attached
to their surfaces. This means the air sticks to and follows the
surface closely. At high speeds it’s easy for the air to
fly away from the surface if that surface changes direction suddenly and this is called
airflow detachment. Detached airflow is mostly not desired as
it greatly reduces downforce and increases the risk of turbulent further down the body.
But whatever kind of attachment pattern you’re looking for, you can spot it with Flow Viz,
for the most part. If the airflow is attached it will carry and
spread the dye along the body of the surface. A nice, strong, continuous attached flow will
show itself by trailing a lot of dye along the area of the attached flow.
If the air tends to detach from the surface it won’t be able to drag the Flow Viz paint
and you’ll see gaps on the bodywork with a distinct absence of paint.
There is a limitation here, however. Often airflow detachments will occur at higher speeds
and if the paint has already been allowed to flow through the lower speeds as the car
accelerates up to top speeds it may be very difficult to spot that this is happening from
Flow Viz alone. In this shot of the Red Bull rear wing we
can see some detachment from the underside here among otherwise strong, attached flows.
Here is looks like there’s some detachment though it may just be an unpainted area.
This show of the McLaren diffuser shows where the airflow sticks and detaches to the underbody
shape. Here, of course, some detachment may be part of the design.
Again, we don’t know what tests are being run so we can’t overstate what we’re looking
at but we can take a lot of interest in the areas being studied.
For example, Sauber here are clearly evaluating how the air flow disrupted by the front wing
continues to behave all the way down the side of the car.
Here the McLaren is checking how the air front the front wing flows through the bargeboards
and turning vanes. Here it looks like McLaren are specifically
evaluating the efficiencies of the airflows on the left and right sides of their car separately,
to have a look at the differences on a specific track.
Flow Viz paint is a striking but limited method for confirming aerodynamic expectations on
track. Teams will often get a lot more data from their wind tunnels and these pitot tubes
structures but Flow Viz continues to be a quick and easy way to sign everything off. And speaking of quick and easy ways of getting
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