Unstable free jet in diffuser
 

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).

http://kepfeltoltes.hu/thumb/120105/...toltes.hu_.png
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

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

Coanda effect
 

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