Divebomb technical support #2: Basic aerodynamics
The Bernoulli principle is mentioned a lot on the official Formula 1’s(F1) channels’ Tech Tuesday. But what is actually hiding behind this fancy name?
Written by Ive Bauk, Edited by Hazel Alagappan
Bernoulli principle is one of the key principles in fluid dynamics (fluids are gases and liquids). It states that, an increase in the speed of a fluid occurs simultaneously, with a decrease in static pressure.Unless you are a an amatuer physicist or have any interest in this area, his definition might not be that easy to understand so I will try to explain it in laymans terms.
First of all, it is important to understand the difference between static pressure, and dynamic pressure. Static pressure is the pressure inside a flowing fluid, whilst dynamic pressure is the physical force exerted on an area and is calculated by the formula P=F/A. Most talk of pressure in aerodynamics refers to static pressure.
The Bernoulli Principle is actually derived from Bernoulli equation which states that in a horizontal pipe,the sum of the static and dynamic pressure is a constant. Meaning that if, for example, static pressure increases, dynamic pressure has to decrease by the same amount.
I know this is still very confusing, but this example is probably going to clarify it a bit more.
Imagine you have a kind of fluid moving through the pipe at a specific speed V1 and dynamic pressure P1. Now what happens if this fluid reaches narrowing (A2)? The dynamic pressure of that part of the pipe will increase too, with the static.
So, as force stayed the same and area decreased, dynamic pressure is increasing. And now, that increased dynamic pressure makes fluid accelerate, V2>V1. As the Bernoulli equation dictates, if dynamic pressure increases, static pressure has to decrease accordingly.
Now that we know what the Bernoulli Principle is, it’s time to look at how that applies to F1.
Let’s look back at the rake angle and what it means.
Imagine that the area underneath the car is a pipe we used to explain Bernoulli principle (so-called Venturi pipe) but the difference is that in this example we have opposite effects.
The area isn’t narrowing, instead it’s widening thus dynamic pressure actually increases and therefore static pressure is decreasing. As you probably already know, we want static pressure underneath the car to be as low as possible to create as much downforce as possible.
So why wouldn’t all the cars have a very high rake philosophy?
There are a few reasons, firstly, lower pressure underneath the car means less influential diffuser, although, this characteristic has proved to be very useful for 2021 regulation changes as all of the low rake cars suffered huge losses in the rear downforce because their diffusers was much more influential and once they got regulated they lost loads of downforce. Bigger rake also means that the car will have a higher center of gravity which brings less stability, also the car itself has to be higher so it creates more unwanted drag.
Each of the teams has implemented different philosophies, as we’ve seen before, it’s not necessarily a matter of which is best,but rather about the implementation and drivers personal preferences.