Quote:
Originally Posted by freebeard
Rotating cylinders? Could you use a rotating cylinder at the stagnation point to effectively move it to ground level?
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*Prandtl worked with a stationary,'sealed' cylinder,in a water tunnel.The slot was formed at one of the downstream sides,with vacuum applied to the slotted 'can.'
*Later,the 'can' would be replaced by a wing section,then flaps.
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*A moving (rotating) cylinder was investigated by Magnus after he noticed the drift of spinning KRUPP-type artillery shells (think of a flying soup can).
*The rotation (from the rifled cannon barrel) created lift,throwing the shell off trajectory.
*Magnus reversed the phenomenon to create the rotating cylinder ship sail.
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*'moving wall/moving skin' boundary layer control has been investigated and is reported about in 'Boundary Layer Theory', Hermann Schlicting's self-published book.
*It hasn't come up yet,so I've not prepared any material on it.
*If the surface moves at local velocity the boundary layer never forms,like at the tire tread/road interface.
*Theoretically,if you had a lubricated,elastic outer skin surrounding a low friction-surfaced body,and you could continuously orbit the skin,matching the local air velocity,you could eliminate the boundary layer.
*A 'backwards-rotating' cylinder at the forward stagnation point would:
- create a pressure spike behind itself as the air crashed into the high Reynolds number 'moving' body surface boundary downstream,triggering an instantaneous transition to full TBL.Probably shockwaves too,which would be audible.
- The boundary surface on the underside of the cylinder would already be moving at 2X the local airspeed plus the Prandtl line of discontinuity acceleration velocity component,and with a TBL already established, trigger separation at what would normally be the stagnation point.
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*The inviscid flow which is typically just outside the boundary layer would still be governed by viscosity effects of displacement dynamics/thermodynamics and remain affected by the isoenergetic Bounoulli rules regarding velocity and pressure within streamline filaments,and we'd still have to 'streamline' the shape,or we'd have separation-induced pressure drag.
*It doesn't bode well.
