Turbulent Dissipation Rate Field Function

osulax · April 3, 2017, 09:49

Hello Everyone,

I am working on modeling a centrifugal pump using K-epsilon turbulence specification and I noticed one of the field functions available to me is "Turbulent Dissipation Rate", "Turbulent Kinetic Energy" is also available. Would it be correct to use these field functions as my K and epsilon values in my physics initial conditions?

For the inlet and outlet I calculated the values using the pipe conditions but I am lost on how to calculate the initial condition of the pump main body in the same way. Mostly confused on how to set a free stream velocity when the whole pump has vastly varying velocities.

I am currently running a simulation using the field function values but it has not converged yet, but I am also not many intervals in. I am starting to think that since the field functions are probably updating in every variable, the solution may not converge since the initial conditions are changing at every interval. However, the solutions I am seeing so far for pressure drop across the inlet and outlet are the closest I have seen to the actual measured data that I have.

Does anyone have any input on whether these functions are valid to use? If not can someone please point me to where I can learn to calculate the K and epsilon for the pump initial conditions?

Thank you

fluid23 · April 5, 2017, 15:15

I am not sure I follow... you want to use field function values to initialize a solution? That is like saying you need gasoline to get to the gas station in order to buy gasoline. Maybe I am missing something.

You aren't going to be able to calculate and apply initial conditions for k and epsilon across your whole domain. How are you calculating the inlet/outlet initial conditions? I think you may be putting too much stock into the initial conditions. Yes, they can make a difference but they are just there to give the solver somewhere to start from. The more important aspect here is how is the solver progress to your answer... not so much where it started. Having good initial conditions may just get you to the answer sooner... Remember, its the destination that matters and not the journey.

April 3, 2017, 09:49	Turbulent Dissipation Rate Field Function	#1
osulax New Member Shawn Join Date: Mar 2017 Posts: 2 Rep Power: 0	Hello Everyone, I am working on modeling a centrifugal pump using K-epsilon turbulence specification and I noticed one of the field functions available to me is "Turbulent Dissipation Rate", "Turbulent Kinetic Energy" is also available. Would it be correct to use these field functions as my K and epsilon values in my physics initial conditions? For the inlet and outlet I calculated the values using the pipe conditions but I am lost on how to calculate the initial condition of the pump main body in the same way. Mostly confused on how to set a free stream velocity when the whole pump has vastly varying velocities. I am currently running a simulation using the field function values but it has not converged yet, but I am also not many intervals in. I am starting to think that since the field functions are probably updating in every variable, the solution may not converge since the initial conditions are changing at every interval. However, the solutions I am seeing so far for pressure drop across the inlet and outlet are the closest I have seen to the actual measured data that I have. Does anyone have any input on whether these functions are valid to use? If not can someone please point me to where I can learn to calculate the K and epsilon for the pump initial conditions? Thank you

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April 5, 2017, 15:15		#2
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	I am not sure I follow... you want to use field function values to initialize a solution? That is like saying you need gasoline to get to the gas station in order to buy gasoline. Maybe I am missing something. You aren't going to be able to calculate and apply initial conditions for k and epsilon across your whole domain. How are you calculating the inlet/outlet initial conditions? I think you may be putting too much stock into the initial conditions. Yes, they can make a difference but they are just there to give the solver somewhere to start from. The more important aspect here is how is the solver progress to your answer... not so much where it started. Having good initial conditions may just get you to the answer sooner... Remember, its the destination that matters and not the journey.