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Trip the boundary layer
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Ribbing, zig-zag strips, and dimples work on most trailing surfaces, even with designs that have laminar flow designs. Anything that can trip the boundary layer and get it to stay attached to the form will help with the aerodynamic (or hydrodynamic) performance. I've seen the effects of this myself in my streamlined recumbent racing vehicle development. Best regards, Jeff Bales Tucson, AZ |
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The angle of the hatch is around 20 degrees at that point. Something else to keep in mind is that the boundary layer grown thicker farther back on the vehicle, so I might have been seeing the tufts fluttering from that affect, too. I want to try adding a trip layer to the rear window on my car, but it would be a b i t c h! to clean, and I'm sure it would collect dirt and look really nasty in no time. |
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Golf ball dimples don't reduce drag. The dimples increase drag.
So why do dimples make golf balls travel farther? It's because the flying balls have backspin imparted by the angled club head. The backspin creates a low pressure area above the ball and a high pressure area under the ball, so that it stays in the air longer. Longer time in the air = longer distance. Dimples accentuate this "Bernouli" effect. Dimples will increase automobile drag. |
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Semantically, the issue of dimples vs. drag really isn't so black and white. I think that in terms of automotive application it pretty much is, however it cannot be ignored that when utilized in the right way, they can reduce the wake of an object, and consequently, the drag. Utilized incorrectly, they will increase drag.
It's also worth noting that dimples work for objects with varied orientation dynamics to the direction of airflow. In other words, on a golf ball, it doesn't matter which side is facing the airflow, the dimple pattern is always oriented in a way to create the desired effect. Cars, boats, and planes in contrast are always more or less oriented the same way into the flow, so there is no need to use the more dynamically effective dimple design, and instead the more directional linear boundary trip could provide greater benefit in the right place. |
So instead of dimples, what about a strip of thick tape just before a rear window drops off? That's the idea with the zigzag tape right?
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I meant that I wanted to add something to trip the boundary layer and help airflow remain more closely attached to the rear of the car, something like zig-zag tape or? I was thinking of using clear silicone caulking. It can be applied almost anywhere, in various shapes and patterns, the thickness can vary, it's not too noticeable, and it's removable. The drawback is that, as I mentioned, if applied to a window it would collect dirt and be tough to clean for good visibility. |
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