Unstable free jet in diffuser

Roland R · January 5, 2012, 07:49

Hello,

I made a 3D simulation which contains a thin tube (after the inflow), a diffuser and a thick tube (before the outflow ). Value of Re number is about 70000. I tried to complete the simulation with different simulation types (steady state and transient), with different advection schemes but the result was same in every case (it can be seen at the figure).

A képet a Képfeltöltés.hu tárolja. http://www.kepfeltoltes.hu

Center of the free jet is not straight after the thin tubes, it is not parallel with the centerline of the tubes.

The geometry is symmetrical, therefore I don’t understand this. Is it a numerical error or a realistic unstable phenomenon?

Regards
Roland

ghorrocks · January 8, 2012, 19:44

I cannot access the link. But symmetric geometry resulting in asymmetric flow is quite typical in fluid flow.

khaydar · January 30, 2012, 16:26

It may has something to do with the so-called coanda effect.

January 5, 2012, 07:49	Unstable free jet in diffuser	#1
Roland R Senior Member Roland Rakos Join Date: Mar 2009 Posts: 131 Rep Power: 17	Hello, I made a 3D simulation which contains a thin tube (after the inflow), a diffuser and a thick tube (before the outflow ). Value of Re number is about 70000. I tried to complete the simulation with different simulation types (steady state and transient), with different advection schemes but the result was same in every case (it can be seen at the figure). A képet a Képfeltöltés.hu tárolja. http://www.kepfeltoltes.hu Center of the free jet is not straight after the thin tubes, it is not parallel with the centerline of the tubes. The geometry is symmetrical, therefore I don’t understand this. Is it a numerical error or a realistic unstable phenomenon? Regards Roland

January 30, 2012, 16:26	Coanda effect	#3
khaydar New Member Join Date: Aug 2010 Posts: 1 Rep Power: 0	It may has something to do with the so-called coanda effect.

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January 8, 2012, 19:44		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	I cannot access the link. But symmetric geometry resulting in asymmetric flow is quite typical in fluid flow.