Aerodynamics 101
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Aerodynamics 101
I figure I should start this thread. Some of you may cry, but at least some of you will understand why I b**** a lot about rice...maybe.
Disclaimer: Don't b!tch at me if you know this.
I won't go too much into the mathematical concepts and 3D analysis, along with the non-dimensional Reynolds number for speed times size comparisons from scale model to full size model. That's beyond the scope of what I'll be explaining anyway...and I'm sure I'll lose like 90% of the people anyway. (And yes, I know that the Reynolds number can be used to quantify the product of speed vs time...)
I will update some of this information from time to time, but if anyone feels that they can contribute to this, then please PM me.
<u>Aerodynamics 101</u>
Boundary layer
This is probably the best concept to talk about first. The boundary layer. What is it? In a more elaborate definition, it's the layer of rapid change in the tangential velocity, where it's thickness is small at the front, but can become rather thick towards the rear of a streamlined car. Like you probably guessed,
the thicker the boundary layer is, the more viscous friction drag is created.
But it Layman's terms...it's the layer that "sticks" to the surface of your car. "Stick" is sort of a pushing the definition, because as you'll see in the diagram below, if there are "laminar bubbles" that occur:
In the diagram shown, you see that the turbulent boundary layer is caused by the laminar bubbles. Those red, circular arrows are supposed to be on the surface the Lotus Sport Exige...not into it like I did. Sorry, but I could make them any smaller.
Two main reasons as to why these little bubbles are worth mentioning:
1.) The laminar bubble area is sensitive, so the flow can separate without reattaching back to the "skin" of the car. What's this mean? Aerodynamic drag. It's like having your winshield set at 90 degrees with the hood. If that happens, then think of the bubble being extremely larger...meaning more drag.
2.) You can force the transition from laminar to turbulent so that you create the bubbles to induce drag, because you reduce separation flow.
Contradicting? Not really. In the most basic terms, you don't want a 90 degree windshield to your hood. Ideally, you see the Lamborghinis which have a smooth angle between the the hood and the winshield. Granted, they are mid-engines, but as for our cars, the idea is to reduce those bubbles as much as we can. But they can be useful, b/c if you can minimize these bubbles without creating a lot drag, the separation flow (which means the flow of air over the car starts to separate, creating turbulent air) can be reduced.
Think of it as this: If you hang a long scarf dangling out the window, you see the scarf flapping around like crazy. Reduce the amount of scarf hanging out, the dangling is reduced. But also notice that when you get a certain amount of the scarf hanging out, the scarf almost doesn't seem like it's moving (granted, we don't live in a perfect world, so you'll see it move a little bit). You create drag, but you also reduce the separating flow (meaning you reduce turbulent air over the scarf). Granted, you've also created a underneath the scarf, we won't get into those those details. tongue.gif:
Naca Ducts
Notably, NACA ducts are used by exploiting this boundary layer. Since the boundary layer usually follows the "skin" of the car, the boundary layer can be used for these ducts. Basically, the duct gets wider, allowing a rapid air increase through the duct.
That's all for the boundary layer. I'll post up more information when I have time on other topics, like spoiler designs, reducing drag, and any other topics you guys want.
Disclaimer: Don't b!tch at me if you know this.
I won't go too much into the mathematical concepts and 3D analysis, along with the non-dimensional Reynolds number for speed times size comparisons from scale model to full size model. That's beyond the scope of what I'll be explaining anyway...and I'm sure I'll lose like 90% of the people anyway. (And yes, I know that the Reynolds number can be used to quantify the product of speed vs time...)
I will update some of this information from time to time, but if anyone feels that they can contribute to this, then please PM me.
<u>Aerodynamics 101</u>
Boundary layer
This is probably the best concept to talk about first. The boundary layer. What is it? In a more elaborate definition, it's the layer of rapid change in the tangential velocity, where it's thickness is small at the front, but can become rather thick towards the rear of a streamlined car. Like you probably guessed,
the thicker the boundary layer is, the more viscous friction drag is created.
But it Layman's terms...it's the layer that "sticks" to the surface of your car. "Stick" is sort of a pushing the definition, because as you'll see in the diagram below, if there are "laminar bubbles" that occur:
In the diagram shown, you see that the turbulent boundary layer is caused by the laminar bubbles. Those red, circular arrows are supposed to be on the surface the Lotus Sport Exige...not into it like I did. Sorry, but I could make them any smaller.
Two main reasons as to why these little bubbles are worth mentioning:
1.) The laminar bubble area is sensitive, so the flow can separate without reattaching back to the "skin" of the car. What's this mean? Aerodynamic drag. It's like having your winshield set at 90 degrees with the hood. If that happens, then think of the bubble being extremely larger...meaning more drag.
2.) You can force the transition from laminar to turbulent so that you create the bubbles to induce drag, because you reduce separation flow.
Contradicting? Not really. In the most basic terms, you don't want a 90 degree windshield to your hood. Ideally, you see the Lamborghinis which have a smooth angle between the the hood and the winshield. Granted, they are mid-engines, but as for our cars, the idea is to reduce those bubbles as much as we can. But they can be useful, b/c if you can minimize these bubbles without creating a lot drag, the separation flow (which means the flow of air over the car starts to separate, creating turbulent air) can be reduced.
Think of it as this: If you hang a long scarf dangling out the window, you see the scarf flapping around like crazy. Reduce the amount of scarf hanging out, the dangling is reduced. But also notice that when you get a certain amount of the scarf hanging out, the scarf almost doesn't seem like it's moving (granted, we don't live in a perfect world, so you'll see it move a little bit). You create drag, but you also reduce the separating flow (meaning you reduce turbulent air over the scarf). Granted, you've also created a underneath the scarf, we won't get into those those details. tongue.gif:
Naca Ducts
Notably, NACA ducts are used by exploiting this boundary layer. Since the boundary layer usually follows the "skin" of the car, the boundary layer can be used for these ducts. Basically, the duct gets wider, allowing a rapid air increase through the duct.
That's all for the boundary layer. I'll post up more information when I have time on other topics, like spoiler designs, reducing drag, and any other topics you guys want.
