Aerodynamically inclined?
08-18-2019, 12:51 PM
#1
Aerodynamically inclined? Long shot but do we have any aerodynamics gurus here, because I sure as hell ain't one LOL
I'm building my street car, a 96 Impala SS with an overdriven/ported LSA supercharger on top of an LSX B15 crate engine.
for my heat exchanger placement I didn't want to obstruct the AC condenser/Radiator stack fully and I found I could get a lot more surface area by mounting it behind where the bumper support sits now (going to build a new bumper support that doesn't obstruct the HX) rather than in the grille area between the headlights, completely blocking the AC condenser and radiator.
This would place the HX completely behind the bumper cover though. Simple people call for simple solutions, so my plan was just to cut a hole in the bumper cover like what you see in the car in this link, just a little bigger.
https://www.procharger.com/gallery/1...et-impala-ss-0
at slow speeds, I'm sure this will allow air to flow freely into the HX. What i'm worried about is what will happen at high speeds?
will air just pass over that hole and continue into the grille, making it completely useless?
will this work against the low pressure area that the air dam creates behind the rad support and either hinder air flow to the radiator or cause reversion?
will this screw up the aerodynamics of the car completely and cause me to veer off into the sky towards Kansas someplace during a standing mile event, if I ever should partake in one?
I could use some advice here. Not looking to race salt flats here but just want to make this work without causing too much of an issue, and my knowledge of aerodynamics is limited to knowing which way a fart will blow in the wind. My question is mainly focused on the air flow aspects for cooling, but I also don't want to disturb the stability of the car at high speeds as the car will have more than 3 times the HP it was designed for.
I'm building my street car, a 96 Impala SS with an overdriven/ported LSA supercharger on top of an LSX B15 crate engine.
for my heat exchanger placement I didn't want to obstruct the AC condenser/Radiator stack fully and I found I could get a lot more surface area by mounting it behind where the bumper support sits now (going to build a new bumper support that doesn't obstruct the HX) rather than in the grille area between the headlights, completely blocking the AC condenser and radiator.
This would place the HX completely behind the bumper cover though. Simple people call for simple solutions, so my plan was just to cut a hole in the bumper cover like what you see in the car in this link, just a little bigger.
https://www.procharger.com/gallery/1...et-impala-ss-0
at slow speeds, I'm sure this will allow air to flow freely into the HX. What i'm worried about is what will happen at high speeds?
will air just pass over that hole and continue into the grille, making it completely useless?
will this work against the low pressure area that the air dam creates behind the rad support and either hinder air flow to the radiator or cause reversion?
will this screw up the aerodynamics of the car completely and cause me to veer off into the sky towards Kansas someplace during a standing mile event, if I ever should partake in one?
I could use some advice here. Not looking to race salt flats here but just want to make this work without causing too much of an issue, and my knowledge of aerodynamics is limited to knowing which way a fart will blow in the wind. My question is mainly focused on the air flow aspects for cooling, but I also don't want to disturb the stability of the car at high speeds as the car will have more than 3 times the HP it was designed for.
09-28-2019, 01:16 PM
#2
Teching In
Join Date: Jun 2008
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The bumper is out front, it gets the air first, even at high speed. Make sure you have a place for the air to go after the cooler. Ideally, all coolers are ducted on both sides. With a well designed duct, you only need a small area to feed a large cooler, about 1/6 the area is enough. But ducts take space. At the least, leave a path to a low pressure area. Venting to the sides or top is good and reduces front end lift.
09-28-2019, 02:26 PM
#3
TECH Fanatic
It's really difficult to say honestly, but I can tell you you want to be careful with the amount of turbulence under the car. I'm not an engineer or anything, but I have spent half my life around aircraft and working on them. Part of that is understanding basic aerodynamic principles, which apply to everything, including cars, and especially if you are looking to NOT mix up the respective fields by making your car into an aircraft. So here goes, apologies on the length, but this is my attempt at a crash course in aerodynamics and basic principles therein.
Bernoulli's principle states that as the velocity of a gas increases, the pressure decreases. To do this on a wing (or rotor blade), we simply curve the top of the airfoil. This causes air to travel farther and therefore faster over the top and create a low pressure area above the wing, which gives us lift. Pitching the wing, or blade, essentially slows the air down under the airfoil even more, and the air going over the top has to go even faster to meet it at the back. That part about the air meeting back up is important. Because if it didn't, it would basically create a "vacuum" space void of any gas, but we know this does not happen. Air over top does indeed speed up to keep from making black holes in the sky. So knowing this, the only other thing it can produce is drag, when this air circles back on itself and causes what we refer to as a "stall" or vortex state.
Why does this matter for cars? Well, what shape IS a car anyway? Does air going over top have to travel farther than the air underneath? Yes. Yes it does. So, wouldn't this mean that there is a low pressure area over the car? You bet your *** there is. If you want to test that, take a spin with someone that has T-Tops, roll the windows all the way up with the tops off and take to 130+, if you dare. It will literally feel like it's trying to suck you out, and the car will start feeling pretty light lol. Ask me how I know... LOL.
So how do cars not lift up off the ground? Two reasons here. First, the physical weight of the car. This may seem obvious, but if speeds are achieved well over what it was designed for, there is a potential to have the car simply lift off the ground and go flying through the air, simply from a gust of wind. There is a famous video of this occurring to several Lemans cars going down a straight away. They just "start flying" for no particular reason.
The second reason is the built in features that limit Bernoulli's effect. The most obvious one is what we call a "spoiler" which is essentially an upside down wing. This "spoils" the airflow, and stops the air from immediately meeting behind the car, as it would on a normal wing. On a 4th gen Camaro, it's quite literally an upside down wing. It essentially creates an "up flow" behind the car, while providing down force. What this ends up doing is creating drag behind the car instead of lift over top, and changes the center of lift. Other features like air dams limit the amount of air that actually flows under the car. The less air you let under the car, the less down force you will need to prevent creation of lift, therefore the less drag you create, in theory. Some high end manufactures actually count on this, and cover the entire underside of the car in carbon fiber to create essentially what is a wing shape under the car. The Shelby Series 1 incorporates this design. It also produces enough down force at high speed greater than the weight of the car, meaning that in theory, it could drive on the roof of a tunnel and stick.
The last thing I will go over is turbulent air. Turbulent air has greater pressure than free flowing air, because it is swirling around at random speeds, in all directions. This increases the pressure of that air. When airflow over top the car is free flowing, as it normally would be, the pressure differential from turbulent air under, and free air over, can start creating potential for lift. So again, the trick is to limit how much air actually is able to flow under the car, in theory. You won't see to many race cars that are more than an inch or two off the ground in the front.
Venting the air somewhere, say through and out the hood compartment would create some turbulent air above the car instead of under it, and add in some additional benefits like cooling the engine and radiator. I would definitely not remove the air dam though, as it has it's reason for being there (limiting airflow). Another popular option is lowering the front of the car an inch or two, to create natural down force using the shape of the car to your advantage.
Can't say I have done exactly what you are doing, but I have pushed close to 200 before, and my car just kept getting heavier from down force. It's also lowered, so I can definitely say that helps, in theory and in practice. I intend to do something similar in the future to mine, and completely redo the front end for cooling purposes because the stock design is straight trash IMO for 4th gen F-bodies. I intend to vent the air out the back of the hood. Might just cut the back of my cowl out to accomplish this. Should work great in theory, considering all things above.
Hope that helps?
Bernoulli's principle states that as the velocity of a gas increases, the pressure decreases. To do this on a wing (or rotor blade), we simply curve the top of the airfoil. This causes air to travel farther and therefore faster over the top and create a low pressure area above the wing, which gives us lift. Pitching the wing, or blade, essentially slows the air down under the airfoil even more, and the air going over the top has to go even faster to meet it at the back. That part about the air meeting back up is important. Because if it didn't, it would basically create a "vacuum" space void of any gas, but we know this does not happen. Air over top does indeed speed up to keep from making black holes in the sky. So knowing this, the only other thing it can produce is drag, when this air circles back on itself and causes what we refer to as a "stall" or vortex state.
Why does this matter for cars? Well, what shape IS a car anyway? Does air going over top have to travel farther than the air underneath? Yes. Yes it does. So, wouldn't this mean that there is a low pressure area over the car? You bet your *** there is. If you want to test that, take a spin with someone that has T-Tops, roll the windows all the way up with the tops off and take to 130+, if you dare. It will literally feel like it's trying to suck you out, and the car will start feeling pretty light lol. Ask me how I know... LOL.
So how do cars not lift up off the ground? Two reasons here. First, the physical weight of the car. This may seem obvious, but if speeds are achieved well over what it was designed for, there is a potential to have the car simply lift off the ground and go flying through the air, simply from a gust of wind. There is a famous video of this occurring to several Lemans cars going down a straight away. They just "start flying" for no particular reason.
The second reason is the built in features that limit Bernoulli's effect. The most obvious one is what we call a "spoiler" which is essentially an upside down wing. This "spoils" the airflow, and stops the air from immediately meeting behind the car, as it would on a normal wing. On a 4th gen Camaro, it's quite literally an upside down wing. It essentially creates an "up flow" behind the car, while providing down force. What this ends up doing is creating drag behind the car instead of lift over top, and changes the center of lift. Other features like air dams limit the amount of air that actually flows under the car. The less air you let under the car, the less down force you will need to prevent creation of lift, therefore the less drag you create, in theory. Some high end manufactures actually count on this, and cover the entire underside of the car in carbon fiber to create essentially what is a wing shape under the car. The Shelby Series 1 incorporates this design. It also produces enough down force at high speed greater than the weight of the car, meaning that in theory, it could drive on the roof of a tunnel and stick.
The last thing I will go over is turbulent air. Turbulent air has greater pressure than free flowing air, because it is swirling around at random speeds, in all directions. This increases the pressure of that air. When airflow over top the car is free flowing, as it normally would be, the pressure differential from turbulent air under, and free air over, can start creating potential for lift. So again, the trick is to limit how much air actually is able to flow under the car, in theory. You won't see to many race cars that are more than an inch or two off the ground in the front.
Venting the air somewhere, say through and out the hood compartment would create some turbulent air above the car instead of under it, and add in some additional benefits like cooling the engine and radiator. I would definitely not remove the air dam though, as it has it's reason for being there (limiting airflow). Another popular option is lowering the front of the car an inch or two, to create natural down force using the shape of the car to your advantage.
Can't say I have done exactly what you are doing, but I have pushed close to 200 before, and my car just kept getting heavier from down force. It's also lowered, so I can definitely say that helps, in theory and in practice. I intend to do something similar in the future to mine, and completely redo the front end for cooling purposes because the stock design is straight trash IMO for 4th gen F-bodies. I intend to vent the air out the back of the hood. Might just cut the back of my cowl out to accomplish this. Should work great in theory, considering all things above.
Hope that helps?