If you had a bullet hole in your windshield, what would the air flow over and through it be like? Assume the car is relatively well sealed otherwise, and that it’s about dime size.
One thing I know… if that happenned to your '94 Formula Firebird, it wouldn’t help you get to 190.
I suspect it would make a lot of noise, but because the pressure in the car will (eventually) reach an equilibrium point, I would expect no net flow in or out of the hole.
If there is not another opening, say in the back of the car, for air to flow out, then air would have a hard time flowing in to front.
Also the slant of the windshield would probably be directing airflow up and over. So the air would have no real reason to change direction to go in the car.
You might even get air flow OUT from Venturi effects (when driving at high speeds). Airflow, aerodynamics, eddies, etc. are very hard to predict.
You’ll just have to try it.
Well, now, wait a minute. You realize that there has to be some net airflow through the passenger compartment even without the bullet hole, right? Otherwise automobile drivers would eventually suffocate and die, an event which decrease the likelyhood of repeat sales.
Given that, some airflow implies a flow from high pressure to low pressure, the lowest pressure being where the air normally exits. In this case, the area of the bullet hole would likely be the highest pressure area, since it is on the front of the car. So you’d get a cylinder of air coming up over the hood and through the bullet hole in the windshield.
In every car I’ve seen data on, there is high pressure on the windshield because it is essentially part of a leading edge deflecting the flow. If the hole were on a side or back window (unlikely since these windows shatter), then the hole might be in a relative low pressure area and suck air out of the car.
The high pressure on the windshield means you’ll get flow into the hole unless the pressure inside the car is high enough to balance the pressure of the external flow. If the car is well sealed, there will be an initial inflow of air through the hole as speed increases until the internal pressure increases enough to stop the flow. As speed decreases, the reverse would happen, causing outflow to balance the pressure. Any leaks in the car’s seals (doors, through the backseat to trunk seals, etc.) will make it harder to increase the pressure in the car and if the leaks balance the inflow then pressure in the car can’t increase to stop the flow. Most cars don’t seal well unless they’re quite new, so I’d expect a pretty good whistle through the hole.
Hey jonathan woody, good one there buddy. Only, you got the wrong guy! And, my formula did reach 190, dangit! (Not Really)
This should be true in aggregate, but it may be so that the bottom 2/3 of the windshield acts as the deflector and the top is a low pressure zone.
Anyone got a junker they can hit with an Uzi and then take on the interstate to resolve this?
I have an AK-47 but the bullet would go all the way through the back window also, skewing the results (were talking one hole correct?)
Dime-sized? What caliber bullet would do that? My dime measures about 3/4 in. Besides, I think the glass (safety glass) would shatter.
I need to watch more action movies.
Peace,
mangeorge
The OP doesn’t say, but I figured front windshield. In which case the window would be held together by the laminate.
Or less
Tony, sit inside the car and shoot out.
Less than zero?
Cue Bill the Cat
“Phhhhbbbbbbbbbbbbtttt!!!”
oO Ain’t no such thing, babe.
BTW; cars have only one windshield. The rest are windows.
Wear hearing and eye protection. Holy crap.
c’mon havent you seen pulp fiction? it wasnt that loud…
wuss 