Quote:
Originally Posted by freebeard
.
|
TBL is our 'friend.'
* Some momentum from the 'ideal flow' just 'outside' the TBL is transferred by viscous-shearing all the way through the TBL, to the body's surface ( boundary ), something a laminar boundary-layer cannot do.
* All the air immediately adjacent to the boundary is 'dead.' It's completely at 'zero' velocity.
* Since the 'minimum pressure' on the body is 'forwards ' of the aft-body, all the increasing-pressure, aft-body flow 'wants' to be 'forwards' of the aft-body.
* The vertical momentum vector component colliding with the 'dead' air adjacent to the body, is the only thing 'holding' it in its place ( as if a slightly elevated machine gun were 'strafing' an area ).
* If the body surface is angled in excess of just a few degrees more than that of the 'local' streamline's orientation, there won't be enough vertical force vector transmitted into the boundary ( the atmospheric 'bullets' simply 'ricochet' off the top of the dead air ), and the boundary air will begin to 'migrate' forwards, seeking the low pressure upstream.
* This is the 'genesis' of flow separation.