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Old 06-27-2012, 05:45 PM   #101 (permalink)
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Originally Posted by orbywan View Post
OK, I'll try that. Can't wait for it to cool off a little so I can get back on this. Do you think lengthwise strakes running front to back on the belly pans are benefitial enough to try them?

To put it a different way, if you only had time to do one or the other, would you build fairings for the duallies and front wheels, or put lengthwise strakes on the belly pans?
I'm afraid that my answer won't be as good as your question but here's what comes to mind.And I hope some of the other members chime in.
*with the belly pan,the air furthest from the ground should be moving close to the velocity of the air along side the vehicle.If so,then there would be no spanwise flow.Strakes,as developed for aerospace,are to work as a flow fence to sequester air and prevent it from flowing sideways to a region of lower pressure,where it would spin up into an attached vortex.This pressure differential would not be great on a road vehicle.One of the recent land speed record motorcycle streamliners developed in the GALCIT tunnel at Cal Tech exhibited no under body flow disturbance except very close to the wheels,which self-corrected a small distance downstream.They used nothing under the bike except nice smooth bodywork.
*Air under and beside the vehicle is basically flowing back in a straight path,with the lowest kinetic energy unlike over the roof of a car.
*Low-drag vehicles will have wheel fairings to mitigate pressure spikes in the region of the wheels and provide for sectional density of the overall vehicle,allowing only very gentle changes in body cross-section.
*I'd be inclined to go after the wheels before I went into micro-managing airflow.
*get all the pick and shovel work done first,then go after the minute details.
I do have 'strakes' under my diffuser,but they are structural reinforcements for a long sheet metal span and were never intended as a streamlining device.
They could actually hurt in a crosswind.Don't know.

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