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 June 11, 2012, 14:29 #2 Senior Member   Martin Hegedus Join Date: Feb 2011 Posts: 500 Rep Power: 19 A vortex is a byproduct. The various elements which make up the forcing functions for the momentum equation (pressure, viscous forces, etc.) are the driver for the creation, and destruction, of vorticity. Another way to look at it is to take the curl of the momentum equation.

June 11, 2012, 19:48
#3
Member

kiwi
Join Date: Mar 2012
Location: South East Asia
Posts: 58
Rep Power: 14
Quote:
 Originally Posted by Martin Hegedus A vortex is a byproduct. The various elements which make up the forcing functions for the momentum equation (pressure, viscous forces, etc.) are the driver for the creation, and destruction, of vorticity. Another way to look at it is to take the curl of the momentum equation.
Hi, Martin Hegedus,
i agree it is true that pressure drive the flow.Then let us consider the vortex ring which interact with solid boundary. What is reason where" the vortex induce an adverse pressure gradient on the wall"?
I see this kind of sentence very often appears in the article. It is written in such a way that the vortex is the one which drive the adverse pressure gradient.

Or Do i miss anything?

 June 11, 2012, 21:13 #4 Senior Member   Martin Hegedus Join Date: Feb 2011 Posts: 500 Rep Power: 19 You'll need to explain the geometry or show a picture. I gather you have a specific question and I don't understand it. Of course the interaction of a preexisting vortex and a solid wall modifies the pressure field due to the need of the flow to change direction at the wall surface. However, it is something else which created that original vortex. In other words, the vortex is an energy/momentum source and it can be used to do things or it can change form but something (a wall, viscosity, etc) must be introduced to change the form of that energy and/or momentum. A vortex can not change on it's own. It can not, for example, just split into two or burst. Conservation of momentum and energy do not allow for it. IMO, you should not view it as the vortex creating the adverse pressure gradient, you should view it as the interaction of the wall and vortex which creates the pressure gradient. fruitkiwi likes this.

 June 12, 2012, 01:12 #5 Member     kiwi Join Date: Mar 2012 Location: South East Asia Posts: 58 Rep Power: 14 Dear Martin Hegedus, Yup, you are right. When i look back at that particular article, it stated that in the upper site, there is interaction of vortex ring and the rigid wall. The vortex is induced when it enters the chamber. Then it flows in and interact with nozzle tip, then it cause the adverse pressure gradient. Thanks for thorough explanation. i should study more details.