Quote:
Originally Posted by Tesla
So if we assume a linear relationship,
a small car with 3' of roof has say, 3/8" of boundary layer at the end of the roof,
A van with 12' of roof would have 1 1/2" of boundary layer and,
A Semi Trailer with 40' of flat roof would have about 5" of boundary layer.
So this then begs the question,
If a longer vehicle has a naturally thicker boundary layer, and a thicker boundary layer is more stable around a curve than a thinner one, can the taper at the rear of a longer vehicle be sharper than that on a shorter vehicle and still have the airflow attached?
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A thicker boundary layer is
NOT more stable around a curve.
Quote:
We see the Semi Trailer boattail flaps at quite sharp angles of around 10-15°, but the template suggests anything greater than 3-5° at the start of taper and you will get immediate seperation.
So then I have to ask is the template application dependant on vehicle length and shape, how long are the flat sections before tapering, does this have a bearing on how aggressive the taper can be?
We must remember the template taper from the point of greatest camber to the tail, is based on the frontal profile of the template which is a bit of an elongated hemisphere, this profile will roughly fit most road vehicles, like sedans and hatches, but when you start to apply it to wagons, vans and trucks there is an extended section of flat roof and sides which I am starting to think has a significant bearing on template application.
For these long vehicles, it may not be necesary to trip the boundary layer to thicken it, as it is already thicker, it may be that we just need to compress the template a little and actually use a more agressive taper.
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You don't trip the boundary layer to thicken it. You trip it to re-energize it. Also trucks and vans have long flat surfaces along the roof in sides for only one reason, to increase cargo volume. Trucks and vans also have a reason for a sharp taper on the end, to decrease length. Do not confuse design features to curtail cost and fit in size regulations as rules for aerodynamics.