Turbulent kinetic energy and energy dissipation at boundary

mshotm2000 · March 13, 2011, 23:57

I read the help of flow 3d, in the section turbulence boundary conditions it's mentioned that the kT and εT in every mesh cell that has one or more of its faces partially blocked or wholly blocked by a rigid wall. To determine boundary values for kT and εT, the usual procedure assumes a local equilibrium between turbulent shear production and decay processes and a law-of-the-wall velocity profile (Rodi 1980). This leads to the values:
KT=(u*^2)/sqrt(CNU), eT= u*^3/kd
now I want to know these equations are valid for all boundary equations such as user define specified velocity or outflow or other boundary conditions? or these equations are invalid just for wall boundary?

MuxaB · March 14, 2011, 10:22

Hi, these turbulent BC are applied at all walls, including internal and mesh boundaries. they are not used at mesh boundaries where there is no wall - velocity or outflow.

chripasch · December 9, 2016, 05:45

Dear experts,
although this thread is quite old, I did not want to open a new one since my question is related to the original question.

I am wondering if it is (in the meanwhile) possible to define the turbulent kinetic energy (k) and its dissipation rate (epsilon) at freestream inlet boundary conditions with FLOW-3D v11.1 ?

I have a set of field measurement data comprising highly resolved 3D flow velocity data allowing for calculating the turbulent kinetic energy from the velocity fluctuations. Besides using the flow velocities, I would like to provide the turbulent kinetic energy at the upstream boundary condition of the model domain.

Any ideas/ hints or the like? I really appreciate your help!

Best regards and thank you in advance

thunde47 · December 9, 2016, 12:29

You can specify turbulent kinetic energy and dissipation values from the bottom left of boundary conditions tab, where it says Turbulent quantities.

chripasch · December 12, 2016, 10:44

Dear "thunde47",
thanks for your reply. I knew this option, but I wasn't sure due to the reply posted by "MuxaB" in 2011. But checking the manual of version 11, it is stated on page 685:

"At inflow boundaries, the user can specify turbulent kinetic energy and dissipation directly. If a value is provided for the turbulent kinetic energy, but not dissipation, then a value for the dissipation will be automatically computed based on the value of Maximum turbulent mixing length defined in the edit box, or default value, if one is not provided."

This is accorsing to your answer - thanks!

March 13, 2011, 23:57	Turbulent kinetic energy and energy dissipation at boundary	#1
mshotm2000 New Member Mahdi Shahrokhi Join Date: Dec 2010 Posts: 4 Rep Power: 15	I read the help of flow 3d, in the section turbulence boundary conditions it's mentioned that the kT and εT in every mesh cell that has one or more of its faces partially blocked or wholly blocked by a rigid wall. To determine boundary values for kT and εT, the usual procedure assumes a local equilibrium between turbulent shear production and decay processes and a law-of-the-wall velocity profile (Rodi 1980). This leads to the values: KT=(u^2)/sqrt(CNU), eT= u^3/kd now I want to know these equations are valid for all boundary equations such as user define specified velocity or outflow or other boundary conditions? or these equations are invalid just for wall boundary?

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March 14, 2011, 10:22		#2
MuxaB Senior Member michael barkhudarov Join Date: Mar 2009 Location: Sante Fe, New Mexico, USA Posts: 337 Rep Power: 18	Hi, these turbulent BC are applied at all walls, including internal and mesh boundaries. they are not used at mesh boundaries where there is no wall - velocity or outflow.

December 9, 2016, 05:45		#3
chripasch Member Chris Join Date: Jun 2014 Posts: 39 Rep Power: 12	Dear experts, although this thread is quite old, I did not want to open a new one since my question is related to the original question. I am wondering if it is (in the meanwhile) possible to define the turbulent kinetic energy (k) and its dissipation rate (epsilon) at freestream inlet boundary conditions with FLOW-3D v11.1 ? I have a set of field measurement data comprising highly resolved 3D flow velocity data allowing for calculating the turbulent kinetic energy from the velocity fluctuations. Besides using the flow velocities, I would like to provide the turbulent kinetic energy at the upstream boundary condition of the model domain. Any ideas/ hints or the like? I really appreciate your help! Best regards and thank you in advance

December 9, 2016, 12:29		#4
thunde47 Senior Member thunde47 Join Date: Dec 2015 Location: India, USA Posts: 133 Blog Entries: 1 Rep Power: 10	You can specify turbulent kinetic energy and dissipation values from the bottom left of boundary conditions tab, where it says Turbulent quantities.

December 12, 2016, 10:44		#5
chripasch Member Chris Join Date: Jun 2014 Posts: 39 Rep Power: 12	Dear "thunde47", thanks for your reply. I knew this option, but I wasn't sure due to the reply posted by "MuxaB" in 2011. But checking the manual of version 11, it is stated on page 685: "At inflow boundaries, the user can specify turbulent kinetic energy and dissipation directly. If a value is provided for the turbulent kinetic energy, but not dissipation, then a value for the dissipation will be automatically computed based on the value of Maximum turbulent mixing length defined in the edit box, or default value, if one is not provided." This is accorsing to your answer - thanks!