velocity-decay constant
 

Dear members,

I working on a generic problem - a free shear flow. The main part of the setup consists of a velocity inlet (Air at 25C). Furthermore there is a sufficient sized computation domain (opening). To investigate the variation with axial distance of the mean velocity along the centerline in the turbulent round jet we consider the velocity decay constant B [Pope, S.B (2008). Turbulent Flows, Cambridge University press]. We began with exhaustive mesh studies. In all RANS simulation cases (k-e, sst) the calculated slope of this line is always too high. We expect a value of B > 5.6. I tried differrent flow regimes especially total energy, because the reynolds number is about 10.000 (Mach number>0.5). My question is, why is the decline of the velocity profile too fast? Any comments a welcome.

Re: velocity-decay constant
 

Hi,

It is well known that many turbulence models have problems getting the decay of a jet right. It is much more expensive but you need to consider DES or LES.

Regards, Glenn Horrocks