# Calculation of initial k for RAS turbulence models

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August 28, 2013, 01:45
Calculation of initial k for RAS turbulence models
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Senior Member

Baris (Heewa)
Join Date: Jan 2013
Location: Japan
Posts: 130
Rep Power: 7
Dear Foam users,

I want to ask about the initial calculation of k (turbulence kinetic energy). I am studying cavitating flow inside of the nozzle with different turbulence models ( kepsilon, RNGkepsilon, kwSST).

According to users guide k is calculated with this formula: k=3/2(u)^2

u corresponds to fluctuating velocity which equals to 5% of inlet velocity. Just i am confused about this point. As you can see in the attached figure i have one domain inlet (Vin=3.1 m/s) and one nozzle inlet (Vin=12.8m/s). AS you know that cavitation and turbulence take place close the nozzle inlet.

I tried both inlet velocity for calculation initial value of k and final result of calculation not change too much, but i want to know that which inlet velocity value should be used for initial calculation of k for the nozzle flows.

thanks in advance.
Attached Images
 nozzle_view.jpg (58.0 KB, 19 views)

 August 28, 2013, 03:52 #2 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,209 Rep Power: 20 i think you better set the values of main entrance for velocity and length(for omega or epsilon formulas) Because only at boundaries you should use a model,the rest of geometry should be solved by the solver itself. Correct me if anyone has another opinion. __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

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