Quote:
Originally Posted by jakobnev
A video in the "I was wrong!" thread reminded me of something I was thinking a couple of years ago but never made a post about.
The idea is that if the flow is turbulent, the air traveling with the car will be mixed with the air nearest to the road, and that this will lead to momentum transfer from the car to the road.
This could be minimized by delaying the onset of turbulence, but without testing it's hard to estimate the magnitude of the effect.
Thoughts? |
* It must be considered on a case-specific basis.
* A JEEP Wrangler will be different of a Citroen DS 19.
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*If a vehicle has an airdam, side skirts, and rear valance of equal ground clearance, no lower than the lowest underbody component, it will essentially carry a pool of dead air with it, as it travels down the road. ( ignoring cooling and wheel openings).
* There would exist some shear-related drag between the dead air and the active flow beneath it.
* A full belly pan insures that the air in this region IS dead, sequestered inside the pan.
* If the entry to the pan is well conceived, the flow will flow down it, with only surface friction drag and no appreciable turbulence-related losses.
* The belly pan does add 'skin' which was formerly turbulence, and a turbulent boundary layer will form on it's bottom, which does, to some degree 'choke' the flow as it grows larger and larger the further downstream.
*This accelerated flow can be beneficial with respect to lower underside pressure and its implication to high-speed stability.
* If you throw in a proper diffuser, total drag and lift can be reduced even more.
The convention since the mid-1970s, is to limit the amount of air flowing under the vehicle, optimizing for drag. For typical driving velocities,the lift kinda sorts itself out automatically.