
[Sponsors] 
December 5, 2023, 03:42 
Sink Term

#1 
New Member
Join Date: Sep 2020
Posts: 25
Rep Power: 5 
Hi,
I'm attempting to incorporate a sink term into the momentum equation. For this, I modified the porosity term in the iowave_velsource.cpp file. Is this procedure correct? For example, will the following code work if I want to include a derivative and specific constants? porousterm= 0.5 * a>u(i, j, k) * fabs(a>u(i, j, k)) + 0.5 * ((a>u(i+1, j+1, k+1)  a>u(i1, j1, k1)) / p>dt*2); for others directions i have kept it as porousterm= 0; I'm not familiar with modifying such scripts, so this approach could be incorrect. Can anyone weigh in on this? Paul 

December 11, 2023, 13:37 

#2 
Super Moderator
Hans Bihs
Join Date: Jun 2009
Location: Trondheim, Norway
Posts: 377
Rep Power: 17 
Just fyi, porous media (Darcy or VRANS) is already included in the CFD model. Please check the B 240 options onwards.
Have a look at this paper: https://reef3d.files.wordpress.com/2...cej_porous.pdf 

December 12, 2023, 00:17 

#3 
New Member
Join Date: Sep 2020
Posts: 25
Rep Power: 5 
Dear Prof. Hans,
Thanks for the reply. I had actually gone through*the paper before, and the reason I did not want to use the VRANS was due to the length scale constraints l<<r<<L. This condition is not true in the case I'm attempting to work with. I'd like to have a sink term like the one in the VRANS equation. (vrans_veg_velsource.cpp) Fi = p>B309*0.25*PI*pow(D_val,2.0)*N_val*((a>u(i,j,k)  un(i,j,k))/p>dt); Fd = 0.5*Cd_val*N_val*D_val*a>u(i,j,k)*fabs(a>u(i,j,k)); But I need it in iowave_velsource.cpp. the porous term modification in iowave_velsource.cpp works fine without the derivative but the moment when i plug in the derivative, ((a>u(i+1, j+1, k+1)  a>u(i1, j1, k1)) / p>dt*2) the simulation crashes with velocity exceeding N61 error. I'd be grateful if you could help me with this. Thanks Paul 

December 12, 2023, 02:40 

#4 
Member
Felix S.
Join Date: Feb 2021
Location: Germany, Braunschweig
Posts: 85
Rep Power: 6 
The Darcy options are also in this study https://www.sciencedirect.com/science/article/pii/S2214166915000028 or here: https://reef3d.files.wordpress.com/2...3d_oe2015.pdf.
Why do you want to calculate the time derivative of the node at (i+1,j+1,j+1), so the node in the top, right, back, and the node (i1,j1,j1), so the node in the bottom, left, front? You know that, i, j, k are the indices of the grid node right? That is why in the vrans_veg_velsource.cpp there is an u(i, j, k) and an un(i, j, k) (the velocity of the prior time step; see vrans_veg.cpp). Why don't you just set B295 to 0, B 308 to 0 and Cd/n/D of B 309 to a value that results in 0.5*Cd_val*N_val*D_val being 0.5, so 1, 1, 1. Also set B 309 to a value that leads to p>B309*0.25*PI*pow(D_val,2.0)*N_val being your Cm value (which is one at the moment). Should result in the thing you want. Or just change Fi in the vrans_veg_velsource.cpp to your liking and set B295 to 0, B 308 to 0. So sth like Fi = 0.5*a>u(i, j, k)*fabs(a>u(i, j, k))+0.5*((a>u(i, j, k)  un(i, j, k))/p>dt*2). And Fd = 0. Hope this helps somehow Cheers 

December 12, 2023, 08:02 

#5 
Super Moderator
Hans Bihs
Join Date: Jun 2009
Location: Trondheim, Norway
Posts: 377
Rep Power: 17 
Darcy porosity is implemented in B240 onwards.


December 24, 2023, 05:55 

#6  
New Member
Join Date: Sep 2020
Posts: 25
Rep Power: 5 
Thank you Felix and hans.
Why do you want to calculate the time derivative of the node at (i+1,j+1,j+1), so the node in the top, right, back, and the node (i1,j1,j1), so the node in the bottom, left, front? You know that, i, j, k are the indices of the grid node right? That is why in the vrans_veg_velsource.cpp there is an u(i, j, k) and an un(i, j, k) (the velocity of the prior time step; see vrans_veg.cpp). As said before, I am still learning how things work. Why don't you just set B295 to 0, B 308 to 0 and Cd/n/D of B 309 to a value that results in 0.5*Cd_val*N_val*D_val being 0.5, so 1, 1, 1. Also set B 309 to a value that leads to p>B309*0.25*PI*pow(D_val,2.0)*N_val being your Cm value (which is one at the moment). Should result in the thing you want. This suggestion would work. Quote:


Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
[waves2Foam] VRANS vs OpenFOAM Sink Term  Felix_Sp  OpenFOAM Community Contributions  3  August 5, 2023 05:43 
How to add Source term (2) for PYROLYSIS  reactingOneDim  Kummi  OpenFOAM  10  April 12, 2021 21:11 
How to add a sink term to the transport equation for the volume fraction in STAR CCM+  ASLAN_1987  STARCCM+  2  March 8, 2021 11:47 
Species Sink Term  Porous Media  Gomaa  Fluent UDF and Scheme Programming  0  July 19, 2018 18:11 
How to add a sink term to the transport equation for the volume fraction  ASLAN_1987  STARCCM+  2  September 14, 2015 21:57 