The Red Bull RB12 maintains most of 2015’s car main features.
What has changed is the opaque paint on the body, as well as the front wing, which is the biggest improvement or at least variation in aerodynamic terms.
This new wing presents cracks and improved small winglets surface’s division that compose the total wing. There’s a simple reason for dividing in smaller parts a bearing element: the adherence of the flow and its streamlines to the same surface of the element.
The principle behind this: every moving body must be surrounded by the relative moving fluid, and we know that for doing this the fluid itself follows the body’s profiles laying down on the surface and closing up when it’s passed.
Schematizing the process we will see the blue flux drawing a trajectory with the same shape of the object’s (ege. wing’s section).
What’s the problem here? What could occur is that crossing the fluid too rapidly this might be ‘stressed’, demanding an excessively fast closing behind the body. This phenomenon can be estimated by Reynold’s number, in the following form:
On the numerator we will have the fluid’s density, speed and characteristic measurement and on the denominator the viscosity.
Characteristic measurement is the main measure describing the body in analysis: if we want to calculate the flux around the ball at a football game D would be the ball’s diameter. In this case, speaking about wings the measure is the chord:
Resulting that for a wing we can consider chord as main measure.
It happens that when we exceed Reynold’s number (depending on the flux, the body’s surface, relative speed) we face a loss of flux’s linearity that modifies the vortex in order to roll up the profile more quickly.
This is not a problem when try to reduce drag because that means having a more adherent flux to the back surface of the body crossing the fluid, generating indeed a greater pressure recovery on the back surface itself. It is bad when we want to create lift, because just as drag decreases so does the lift. So on fast tracks with high speed corners we have a loss of drag performance generated aerodynamically induced, working much more on mechanical grip, using the tyres more and probably losing directionality.
In this sense is useful to introduce a crack that collects additional flow able to adhere to the back side of the profile, with a smaller area to cover and on which close up. This trick consolidates a laminar flux at high speed (especially in the corners) dividing the area and giving to each one a small area to cover on the back, explained in the image below.
Red Bull team has probably aimed to a better management of the flux in order to make it more adherent and create more lift (note that making the flux more linear helps all the air flux surrounding the entire car).
Don’t forget the aerodynamic quality that has always been a distinctive trait of Newey’s cars, even if 2015 season was disappointing in terms of results. If the car has maintained the same shape more or less (except for small innovations) what is really new is on the outside: the opaque paint makes the car the most fancy and stylish car of the season. But that’s not just and aesthetic feature, there’s a specific reason behind the choice. The air flowing on this paint creates an incredible fine vortex layer super adherent to the surface, and the air moving on this layer does it quicker, because moving on this slippery air bearing. This effect is called limit layer: phenomenon occurring when the surface of a moving body inside a flux is not perfectly flat but has some roughness, in which air molecules remained trapped.
These molecules, trapped by viscous drag, cause the other molecules that pass over them a slowdown (even if they are not trapped in the surface themselves). This happens on every small part of the surface, so the bigger the surface, the bigger the limit layer drag improvement will be.
A part of these molecules slowed down by the first flux layer (the one in contact with the surface) are climbed over by another flux layer with which will have other viscous drag and will be slowed down by them. The phenomenon increases when the flux covers the object in length. The longer the object the greater this effect will be.
A very simple example is a flat layer moving inside a fluid like air (just like every car’s roof), and we will note this situation:
We can find another example on a military aircraft, that uses air vortex to have a greater attack wing flux in order to improve aerodynamic performance. The same we can say for F1 cars.
The crucial point is: there’s no difference if I use just one point to focus the vortex or I use an opaque painting all over the car.
Considering these aerodynamic features, and the good results of both cars on the fast paced Shanghai circuit, the setup is still good, and the chassis is rumoured to be the best of the lot. The only thing missing now is some power unit related evolution, in order to get the power missing to be steadily among the best.