Quote:
Originally Posted by Tesla
Thank you, that's the confirmation I was looking for.
It's where all my scratchings and calculations were pointing me, it's more about 3D air pressure and velocity at a particular point in time, rather than a 2D angle on a surface in a singular plane, although one still needs to be wary of a too agressive change at any point, there is some lee way if this is compensated in the adjacent areas.
One of the things I've been looking at with all these different equations is the rate of change of the angle and I think the ideal form has an ever decreasing rate of change, so although the angle is increasing to a max of 22-23°, the actual rate of change between sections, is decreasing, this fits with reducing air pressure as the sectional area gets smaller, so the void is filled slower and hence to avoid seperation each subsequent void must be smaller than the previous one.
If the sectional area decreases too quickly, the void cannot be filled, low pressure areas and drag are the end result.
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What Hucho and all the others want us to bear in mind is that the air in the boundary layer immediately adjacent to the body surface is already at rest.
From Daniel Bournoulli,if we throw to much of a pressure rise at the flow,we're asking it to decelerate from a velocity which is already at zero.If we do it,that air will seek a lower pressure which it will find upstream where the air is faster,creating the reverse-flow which produces the shearing forces leading to separation,eddies,then full-blown turbulence.
The kinetic energy of the turbulence can never be converted to useful pressure regain in the wake and we lose the game right there.