Star-CD and K-Epsilon turbulence model

hamoudi · June 1, 2009, 11:57

Hello Everybody,

I have a simulation on a numerical jet of air For this I use the Star-CD with Turbulence Model K-epsilon
as you know at the beginning of the simulation we need to initialize the values of
K and epsilon ( Energy and Dissipation rate of turbulence )
to calculate these two parameters
Energy
K = 3 / 2 * (U * I)
Velocity of Jet . U = 286 m / s
I= Intensity = 5 %
K= 360,73 m2/s2

Epsilon

Epsilon = (cmu 3 / 4) * K (3 / 2) / L

cmu = 0,09,

L= M ixing Length = 0.07

Epsilon = 1,25 e +04

My simulation diverge always

Please I am waiting for your Answers

****** Is this possible ********

matejfor · July 16, 2009, 08:54

Hi,

in fact you may specify the turbulence at inlet also by turb. intensity and length scale (usualy 0.1 - 0.07 of inlet diameter or characteristic size).

With you high velocity do you calculate the flow as compressible and do you have correct setting of the pressure boundary?

what is diverging, epsilon or continuity (pressure)?

matej

nowhere · July 31, 2009, 05:34

Hi,

I am having a somewhat similar problem. For a model i am only given the intensity and length scale for the turbulence model. How (and where) do I specify them in OF?

June 1, 2009, 11:57	Star-CD and K-Epsilon turbulence model	#1
hamoudi Member Hamoudi djamel Join Date: Apr 2009 Posts: 50 Rep Power: 16	Hello Everybody, I have a simulation on a numerical jet of air For this I use the Star-CD with Turbulence Model K-epsilon as you know at the beginning of the simulation we need to initialize the values of K and epsilon ( Energy and Dissipation rate of turbulence ) to calculate these two parameters Energy K = 3 / 2 * (U * I) Velocity of Jet . U = 286 m / s I= Intensity = 5 % K= 360,73 m2/s2 Epsilon Epsilon = (cmu 3 / 4) * K (3 / 2) / L cmu = 0,09, L= M ixing Length = 0.07 Epsilon = 1,25 e +04 My simulation diverge always Please I am waiting for your Answers **** Is this possible ******

July 16, 2009, 08:54		#2
matejfor Senior Member matej forman Join Date: Mar 2009 Location: Brno, Czech Republic Posts: 182 Rep Power: 17	Hi, in fact you may specify the turbulence at inlet also by turb. intensity and length scale (usualy 0.1 - 0.07 of inlet diameter or characteristic size). With you high velocity do you calculate the flow as compressible and do you have correct setting of the pressure boundary? what is diverging, epsilon or continuity (pressure)? matej

July 31, 2009, 05:34		#3
nowhere New Member nick stoppelkamp Join Date: Jul 2009 Posts: 4 Rep Power: 16	Hi, I am having a somewhat similar problem. For a model i am only given the intensity and length scale for the turbulence model. How (and where) do I specify them in OF?