Calculate pressure from vehicle moving through air

In summary, the conversation is about finding the air pressure generated against a moving car with a flat one square meter grill facing the wind. The formula F=MA in relation to P=F/A was tried, but the vehicle is not accelerating. The concept of stagnation pressure is suggested as a way to estimate the drag on the plate, and looking up "stagnation flow" for a more accurate estimate is also recommended. The use of a drag coefficient for a flat plate is proposed, rather than for the entire car.
  • #1
Cbrown92
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Alright, I've been looking everywhere, and tried to use a few formulas but they don't answer what I'm trying to find. Let's say I have a car that weighs 1815kg )4000 pounds) and its traveling at 90kph (roughly 56 mph) with a flat one square meter (10.76 sq ft.) grill facing the wind as it travels. What is the air pressure (In pascals and psi) I can expect to generate against the vehicle as it moves? Though providing me the answer in Newtons wouldn't hurt either.Also, the vehicle is moving at a constant rate assuming a flat road surface. I'm trying to invent a new kind of engine based on relatively low air pressures
 
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  • #2
What formulae did you try? It's not to hard to find one.
 
  • #3
I tried F=MA in relation to P=F/A but the vehicle isn't accelerating, its moving at a constant rate. Unless I'm confused about the definition of acceleration itself? Is there anything I'm missing?
 
  • #4
You need to look at drag equations...

http://en.wikipedia.org/wiki/Drag_(physics)

eg..

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  • #5
If the front is flat, he doesn't even need to concern himself with the drag equation. He can get a good enough estimate just using the concept of stagnation pressure.

So, in short, just look up "stagnation pressure."

You might also look up "stagnation flow" if you want a more accurate estimate. That would require an integral of the pressure distribution over your flat surface, but that's pretty trivial.
 
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  • #6
Sorry for having taken so long to reply, but if I use a drag coefficient, that accounts for the drag in its entirety not a specific sectional area. Stagnation pressure, from what I understand applies to pressure in pipes. I guess what I'm trying to find out is the amount of drag on that single plate of which measures 1sq meter in area at speed, and then how to transition that into pressure and calculate for higher and lower speeds. Think of something about the shape of a Cadillac grille in the front (Similar size even) while ignoring the drag/pressure on the windshield, sides of the car, etc.
 
  • #7
Stagnation pressure applies to any moving fluid, not just pipes. I wouldn't have suggested it if it didn't make sense to use it. Stagnation pressure is just the pressure that results from isentropically slowing the flow to zero velocity. Just calculating the stagnation pressure at the front of a car moving a given speed is going to be a rough estimate of the pressure on the given size of plate. If you want a better estimate, then like I said before, stagnation flow would give you a more accurate estimate.
 
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  • #8
Sorry for having taken so long to reply, but if I use a drag coefficient, that accounts for the drag in its entirety not a specific sectional area.

Not sure what you mean but I was proposing to use the drag coefficient for a flat plate not the whole car (I agree that using the drag coefficient for a flat plate would probably give an over estimate).
 
  • #9
+1 for stagnation pressure.
 

Related to Calculate pressure from vehicle moving through air

1. What is the formula for calculating pressure from a vehicle moving through air?

The formula for calculating pressure from a vehicle moving through air is pressure = 1/2 x density x velocity^2 x coefficient of drag x frontal area. This is known as the drag equation and takes into account the density of air, the velocity of the vehicle, the shape of the vehicle, and the coefficient of drag, which is a measure of how streamlined the vehicle is.

2. How does the speed of the vehicle affect the pressure it creates while moving through air?

The speed of the vehicle has a direct impact on the pressure it creates while moving through air. As the speed increases, the pressure also increases due to the increase in the amount of air being pushed out of the way by the vehicle. This is why high-speed vehicles, such as airplanes and race cars, experience higher levels of pressure than slower moving vehicles.

3. What is the role of the shape of the vehicle in calculating pressure from moving through air?

The shape of the vehicle is an important factor in calculating the pressure it creates while moving through air. A streamlined, aerodynamic shape will experience less pressure than a bulky, non-aerodynamic shape. This is because a streamlined shape allows air to flow smoothly around the vehicle, while a non-aerodynamic shape causes turbulence and creates higher levels of pressure.

4. How does the density of air affect the pressure created by a moving vehicle?

The density of air plays a significant role in the calculation of pressure from a moving vehicle. As the density of air increases, so does the amount of air particles that the vehicle must push out of the way, resulting in higher levels of pressure. This is why vehicles experience higher levels of pressure at higher altitudes, where the air is less dense.

5. Can the pressure created by a vehicle moving through air be reduced?

Yes, the pressure created by a vehicle moving through air can be reduced by making changes to the vehicle's design. This can include making the vehicle more streamlined, reducing its frontal area, and choosing materials with lower coefficients of drag. These changes can help decrease the amount of air resistance and turbulence, resulting in lower levels of pressure and improved overall efficiency.

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