why when the window is open in a car the wind comes in so sporadically when driving
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If air comes in it creates an overpressure in the car, which has to go somewhere. So air comes in and goes straight out after. This makes the horrible „wub-wub“ sound. So if you want your air to come in evenly, you have to open a second window, preferably in the back to get rid of the overpressure.
Edit: This is also the reason your ears sometimes pop when you open your window.
Bernoilli’s principle pulls air from the inside of the car which end up creating a low pressure area. Said low pressure then drags the flow of air inside where the air flow crashes into seats and such. This creates a high pressure area that pushes the flow of air outside the car and we’re back at square one. The air inside the car is constantly cycling between high and low pressure which at high speeds is super distracting.
Modern cars are designed to create as little drag as possible. This means the air flows as smoothly and uninterrupted as possible around the car. This means when you create a void for the flow to “fall” into, the air flow has to fall enough to divert into the car by hitting another surface, like the door pillar at the back of the window opening. When moving at speed, most of the flow is going fast enough to go over the window opening and hit the back window and continue on, same as it was going to. Only a little falls into the opening.
It’s the same way that whistles work. It’s just the resonant frequency is very low. https://youtu.be/O_-2Vo-f1AU
Air gets pushed in but has no where to go, so it bounces back out. You can see this visualized with flames in this slow-motion video of the Barking Dog science experiment: https://youtu.be/c3fJRRCAIdk?t=136
In this experiment the motion of the air is caused by combustion, not a moving car. But either way it’s still air rushing in to an enclosed space.
It’s like blowing across the top of a bottle to make the whistling sound. A car with one open window is the exact same thing – a volume of air with wind blowing across a single opening. And you’re inside the “bottle”.
The bigger the air cavity, the lower the frequency of the resonating air. That’s why bigger bottles whistle a lower note. The car is like a really big bottle, so the frequency is so low it just sounds like thumping.
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