High pressure to low pressure air movement

[freebeard]

I think the difference is that the air doesn't apply force at right angles to it's flow. It's trying to get from fore to aft with the least disturbance.

[aerohead]

Originally Posted by hat_man

I wasn't so much thinking it would generate "thrust". I guess I was seeing X amount of pressure applied to each side of a watermelon seed at the widest part somewhat cancelling each other out (180 degrees apart resulting in a 0). But the same X amount of pressure applied to each side of the tapered part being more than 0 because the side pressures being less than 180 degrees apart. Not that it would result in more than X, but rather a greater percentage of X being "usable". Does that make sense?

I can see the concept in my mind but just can't put it into words. Especially in tech speak.

You're describing the D'Alembert paradox,from long ago,before boundary layer theory was known.D'Alembert figured that there'd be as much pressure at the rearward stagnation point as at the frontal stagnation point.
Due to entropy, derived by kinetic energy converted to heat via viscosity and surface friction drag,it's impossible for there to be as much energy at the back of the body ,as at the front.
We're stuck with losing perhaps 12% of overall energy to skin friction.The good news is,that we can reduce pressure drag by basically 88%.Unless we're driving on the Moon,we're stuck with the 12% loss.

[aerohead]

Originally Posted by freebeard

I think the difference is that the air doesn't apply force at right angles to it's flow. It's trying to get from fore to aft with the least disturbance.

There would always be a component of static barometric pressure acting on the body,or velocity pressure,or some combination of the two.Inviscid flow would be channeling force through the turbulent boundary layer to within one Nitrogen molecular diameter of the body throughout,above 20 mph.

[hat_man]

Thank you everyone.

I'll have to read up on that D'Alembert paradox. Between that and freebeard's comments about how pressure would be more in the direction of air flow, I can see where my ideas were skewed.

This is one of the things I truly appreciate about this site. You folks are always willing to try and educate and share your knowledge, to help someone like me understand.

[freebeard]

Looking for a thread to drop this in. Close enough? https://theansweris27.com/naca-submerged-duct/

theansweris27.com is an interesting site. They show the wind tunnel they replicate in CFD and the mesh representing the atmosphere.



It ends with an example of a Ferrari that moves away from a submerged duct to a more scoop-like form.