Hello,
I am trying to simulate phase change during turbulent flow in comsol multiphysics, for that I require to add an additional sink term at the end of turbulent kinetic energy and energy dissipation rate equation which is 'k' and 'epsilon' equation in turbulent model to include the effect of solidification in the turbulent flow. Can somebody please suggest how to do that.
any suggestion will be greatly appreciated.
-Akshay
Forget this k-eps model. While k is a so-called conserved variable, eps ist not. Eps is a colored mix of variables. I recommend for turbulence the k-Omega-model. It allows in my interpretation (2009) e.g. the derivation of the von-Karman constant as 1/sqrt(2*pi)~0.3989... as well as also other constants of this model. Cheers, Helmut
To add an additional sink term in the k-epsilon turbulent model in COMSOL Multiphysics, you will need to modify the source terms in the transport equations for k and epsilon.
The transport equations for k and epsilon in the k-epsilon model are:
k_t + u_i k_i = P - mu_t k S_ij S_ij - mu_t e
e_t + u_i e_i = C_1 mu_t k S_ij S_ij - C_2 e^2 / k - e / tau_e
Where:
- P is the turbulent production term
- S_ij is the strain rate tensor
- mu_t is the turbulent viscosity
- tau_e is the turbulent time scale
To include the effect of solidification in the turbulent flow, you will need to add an additional sink term on the right hand side of the transport equations for k and epsilon. For example, you could add a term that represents the rate of solidification, which could be a function of the temperature and the solidification rate coefficient.
To implement the modified transport equations in COMSOL Multiphysics, you will need to use the DEFINE_SOURCE function to define the source terms for the k and epsilon transport equations. You can then specify the additional sink term as part of the source terms.
Thank you Mohammad Rahjoo for your response.
Is there any way of adding sink term directly in the k-epsilon equation? since I am using the k-eps model directly from the CFD module in comsol? If I add a volume force term, it is added to the momentum equation, but I also need a similar term to be added to the k and eps equation.
Yes, it is possible to add a sink term directly to the k-epsilon equations in COMSOL. To do this, you can use the "User Defined Scalars and Memory" (UDSM) feature in the CFD Module to define the sink term as a source term in the k-epsilon equations.
Let me know if you need more help!
thank you so much Mohammad Rahjoo your suggestions are very useful to me. I will try to implement it and will get back to you if I stuck somewhere.
Mohammad Rahjoo could you please tell me in brief how can I use UDSM in comsol?
Thanks in advance
-Akshay
Sure Akshay,
I hope this helps!
I am using low-Re k-epsilon turbulent flow module from CFD. On right-clicking that node I am getting boundary condition nodes such as inlet, outlet, symmetry, etc.
model builder-->click the eye of show more options -->open the equation view. Then, add the additional sink terms in k-epsilon turbulent model directly. Next, pay more attention to grid quality and the convergence. hope this work
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