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or maybe like a radiator air diffuser or something...
Dude, you need to watch some tv:Ryan wrote:The dimples on a golf ball are only effective because the golf ball rotates. Unless you're driving incorrectly, a dimpled undertray is an error in logic, or a brilliant marketing scheme, I'm not sure.
Sounds like hindsight bias to me. Eat your beret Ryan! ;DRyan wrote:Yay mythbusters!
In principle, the idea is bulls---.(skin friction is a minor factor for drag in cars... most is from the partial vacuum created behind it) In reality, who knows. Lol. 3 MPG is an impressive increase... for adding a couple hundred lbs of clay to your car. I wouldn't call that a carefully controlled scientific experiment, but aside from mumbo jumbo, I have nothing tangible in response. Interesting.
Thoughts:
Drag is caused by partial vacuum, partial vacuum is caused by flow reversal, flow reversal is caused by seperation.
The dimples stimulate a turbulent boundary layer. Turbulent boundry layer is less prone to seperation, although has higher skin friction.
Ideally, Mythbusters should have done this again, but only dimpling the roof, rear window and trunk. I think they would see their best results then.
You will always create downforce any time you accelerate the air underneath the car and reduce the air pressure, via the Ground Effect. In fact that is one of the primary reasons why diffusers and splitters are used, along with aerodynamics. Definitely not for fuel economy, even if that may be an added benefit.wytbishop wrote:There isn't a great deal of gains to be made under the car. By cleaning up the airflow there is a (small) bit of mileage to be had but you will not be able to create any downforce. Ryan's right though...you potentially have a real problem with flow through the engine compartment if you enclose the bottom.
that's true...but just closing off the underside of the car is not going to accelerate the air passing under the vehicle. Airflow accelerates as it passes over a wing, for example, because the shape of the wing causes it to travel farther than the air passing under the wing. In order to maintain constant flow rate, it must accelerate. Cars which create downforce are shaped on the bottom so that the air passing under the car must travel farther...i.e. an iverted arc...or tunnels are used to create vortices...etc. Just making the bottom of the car smooth will not achieve this at the ground clearance that the MX-3 has, but it will reduce turbulence around the wheels and reduce resistance, improving fuel economy a bit._-Night-Shade-_ wrote:You will always create downforce any time you accelerate the air underneath the car and reduce the air pressure, via the Ground Effect. In fact that is one of the primary reasons why diffusers and splitters are used, along with aerodynamics. Definitely not for fuel economy, even if that may be an added benefit.
http://en.wikipedia.org/wiki/Ground_effect_(cars)