I’m not a fan of the term “aerodynamic” but I think this is an important topic. The term is commonly used to describe a vehicle’s design, but the reality is that it is the airflow moving through the entire vehicle that determines how the vehicle performs. In other words, airflow is the very essence of a car or a plane.
Airflow is the product of a complex set of variables, but the big ones are air pressure and air velocity. The equation that determines the pressure and the velocity is the Bernoulli equation and it’s written out in a lot of equations. The question is how to determine the correct numbers to use. We use a variety of mathematical formulas depending on the situation to get the correct numbers, but it is possible there is something wrong with the equation.
The equation for air flow has not been in the game for the last couple of years, but it appears that it’s pretty straightforward. The equation is known as the Bernoulli equation, and it works quite nicely on virtually any problem.
The Bernoulli equation is commonly used to calculate the pressure of air at any given point in a tube. The pressure is expressed as a percentage of the pressure at the inlet. So if the pressure at the inlet is 10 psi, the pressure at the outlet of the tube is 100 psi.
Just like when you’re trying to find the pressure at the inlet of a pipe or tube, airflow is easy to figure out. The easiest way to do it is to start with the Bernoulli equation and adjust it to account for the pressure at the outlet of the pipe, the pressure in the tube, and any other external conditions. Now, let’s try to figure out the pressure at the inlet of the tube: 10 psi.
That’s easy. Since all you have to do is make the pressure 10 psi at the inlet and we have our pipe with a 10 psi outlet.
So, what does that tell you? Well, it tells us that the pipe has a pressure of 10 psi, but the tube has another 10 psi of air flowing through it. That means that the pressure in the tube is 10 psi more than the pressure in the pipe. Now, the problem is that the Bernoulli equation we just solved won’t tell us the pressure at the outlet of the tube, which is another 10 psi.
The Bernoulli equation tells us that the pressure at the outlet of the tube is 10 psi more than the pressure at the inlet of the pipe. But this new equation tells us that there is an additional pressure of 10 psi flowing out of the tube. I’m not sure how this is going to work out, but I’m going to guess that the pressure of the air in the pipe is less than the pressure of the air in the tube.
So the pressure at the inlet is 10 psi more than the pressure at the outlet of the tube, and the more pressure is flowing out of the tube, the less pressure is flowing in. This is something that is easy to understand just by looking at the diagram that is attached to the equation, but it is a bit difficult to see how this will work out in practice.
I can’t tell you how many times I’ve explained this problem to my kids and asked them what they think of it. Like, I don’t know, a lot of times they tell me they don’t know! Like I’ll ask them if they know why this works. “Because the pressure in the pipe is less than the pressure in the tube”, they say.