Now that we’ve covered the basics in pressure and flow, let’s dig into the more F1 relevant
part of aerodynamics – how to control a wild and unwieldy air flow.
Let’s jump straight back where we left off in the last video then – looking at our
side profile of a wing, with all the air flowing around it.
So neat.
It isn’t always so neat
though, and we’ll get to that.
But first, let’s quickly work out why the air underneath
the wing follows the surface at all.
You see, if you imagine these layers of air
rushing towards the wing all straight like this.
The natural tendancy for this air is
to keep going in the direction it was.
This underneath air will keep going straight and
this deflected air will keep going down (though the fast moving under layers of air should
absorb this) So why does it, in reality, follow the surface
of the wing?
Because, if there’s no (or very little air) here, then that means this
is a very low pressure area.
And, as we discussed previously, high pressure air will flow into
areas of low pressure air.
So all this high-pressure, high energy air is naturally going to bend
into this pocket.
Hi!
I'm just going quickly stop the video here and make a clarification on the last
video.
In that video I said that the air under the
wing moved faster because it was being accelerated by being squeezed.
That's not the whole truth
and the majority of the acceleration comes from the air being pulled into this low pressure
area.
Thanks!
There’s a second, smaller effect going on here too and that’s the friction between
each layer of air.
It begins right at the surface of the wing where the first layer
of air particles actually doesn’t really move at all because it’s stuck to the wing
by molecular forces Each layer of air is attracted to each other,
between the basically static layer of air and the full speed layer of air here, each
layer is moving just a little bit faster due to the friction between each individual layer
of air.
This section is called the boundary layer.
The amount of attraction or friction betw een layers of flow is called viscosity.
This
viscosity is one component of overall aerodynamic drag, because the surface of the wing or car
is tugging on the airflow, slowing it down, which means that – in turn – the air flow
is tugging on the surface, slowing it down.
Right, so now we know why air flow follows
the form of a surface.
Now I’m going to show you when it doesn’t.
Last video I tipped the wing up like this (increasing its angle of attack) and all the
air followed it diligently.
This will give you more downforce, I said.
But actually,
tipping the wing up this high may well ruin everything and give you even less downforce.
You see, if the air is going fast enough, the momentum of the air may overpower the
pull of the low pressure area here and instead, the air will mostly just plough on, being
deflected only slightly towards the wing.
This is called flow separation or detachment.
It should be clear that, with the air flow separated, the average direction of the airflow
after passing around the wing is less upward than if it all stayed together.
This means
that a separated airflow gives you less downforce than an attached airflow.
Between these two flows of air, the air in between doesn’t really know what to do with
itself.
The boundary layer will get sucked away from the surface and then get all garbled
trying to resolve the pressure differences.
This is turbulence.
You may hear it referred
to as ‘turbulent flow’ with the nice smooth airflow called ‘laminar flow’ (laminar
just meaning layered).
Right around the point where the air flow
separates the amount of downforce the wing delivers will drop massively (though the drag
continues to increase) and this is called a ‘stall’
So how do we resolve this problem of separated air flows ruining our nice efficient downforce.
Well, we could just not tilt the wing so aggressively.
But that’s giving up.
We need to find a
way to keep this fast flowing, energetic air attached to the surface for longer.
The answer is vortices.
A vortex is just a spiral of air, spinning like a screw along
the airflow.
So, if we can imagine getting a vortex of air to flow between the attached
boundary layer and high energy separated airflow, you can see how it can start bringing them
together, pulling the high energy detached air into the boundary layer, allowing it to
stay attached for longer, while smoothing out the disturbance between the boundary layer
and the detached layer.
So, in short – a vortex can help keep air
flow attached to the surface it’s flowing around.
This doesn’t just apply to the wing,
but applies to the entire chassis, too.
Consider the car as a whole.
We’ve got a
number of places we want high-energy fast flowing air to go: the airboxes and the huge,
downforce generating rear wing for example.
But before the air can get to those places
it has to navigate the body of the car and we don’t want a separation in air flow to
accidentally send a bunch of weak, turbulent air into the rear wing.
Instead, we can use vortex generators to keep the air attached to the chassis and minimise
turbulent, low pressure flow.
A further downside to air separation is it
causes drag.
Imagine the car body pushing through fast flowing air.
If the air separated
dramatically, this leaves a huge hole in air of the car’s wake – a massive low pressure
area behind the car.
Now with a high pressure area in front of
the car or wing and a low pressure area behind it, this causes a net force to act backwards
on the car, dragging it back , reducing its speed.
You can also think of the low pressure
area creating a suction if that’s easier.
It’s exactly the same thing if a (maybe)
slightly more clumsy way of putting it.
Generating some vortices helps to attach scattered
airflows to the body surfaces and reduces the turbulence in the car’s wake and will
reduce the drag on the car.
And I’ve been showing you a car side on,
but this works in all dimensions.
A lot of work is put into keeping the air attached
right along the side of the car too, to stop the air doing this and to make sure it does
this In fact, one of the major jobs of the front
wing, and the reason it always looks so complex, is to build huge vortices to help the airflow
down the side of the car and to stop it getting mucked up by the mayhem caused to the air
by the spinning tyres.
All of the details and intricately sculpted
tips of a front wing are designed in aid of vortex generation that will help persuade
the air in its flow all the way down the car.
If we take just one element to look at it
we can see how vortices are generated.
So above the wing we’ve got our high pressure
air and below the wing we’ve got low pressure air.
Now, as we know, the high pressure air
will try and flow into the low pressure air to resolve the difference and it doesn’t
have to wait until after the air has passed over the wing to do it.
At the edge of the
wing, here, the top flowing air will try to curl over the wing to get to the bottom flowing
low pressure air.
From here we can see how a corkscrew movement starts at the wing tip
and will continue back down the chassis.
All these wing tip shapes will work together
to create a really huge vortex that doesn’t just help the good airflow follow the shape
of the chassis.
It also keeps the bad airflow – the disturbed, turbulent air in the wake
of the spinning tyre – away from the bodywork, to stop it ruining everything.
These vortices
are the bouncers of an F1 car, telling the drunk tyre airflow to ‘keep on moving sir,
keep on moving’.
So that’s the basics of how you control
airflow and coax it into doing exactly what you want it to do.
The next video will be
a bit of a free for all on little aero bits – what does this thing do, why are there
holes here, what’s a bargeboard?
– that kind of thing.