Solving two additional transport equations.

- December 21, 2020 at 11:38 am
  
  Touq
  Subscriber
  
  Hi, nI would like to check the possibility of solving two additional transport equations. nFor example, in non-premixed combustion model, there are many sub-models such as chemical equilibrium model and diesel unsteady laminar flamelet model. In the chemical equilibrium model, it is possible to introduce a secondary stream which means including a second mixture fraction. Consequently, two additional transport equations will be solved during the real simulation run-time (the transport equations of mean mixture fraction and its variance). This option is not available in diesel unsteady laminar flamelet model. Hence, is it possible to introduce a secondary stream in the diesel unsteady laminar flamelet model, which means solving two additional transport equations during the simulation run-time, using UDF or some other techniques?.
- December 21, 2020 at 3:26 pm
  
  Karthik Remella
  Administrator
  
  Hello,nYes, you should be able to add additional transport equations in Fluent by activating User-Defined Scalars (UDS). Please check out this link from our Fluent Users Guide to understand this better. You should be able to activate this from the User-Defined Tab.nnThese transport equations are solved after the momentum, continuity, and energy equations. Here are some additional details about this.nI hope this helps.nThank you.nKarthikn
- December 21, 2020 at 5:40 pm
  
  DJENDARA
  Subscriber
  
  YES IT'S TRUE THIS IS THE METHOD AND USE UDMI FOR OTHER PARAMETERSn
- December 22, 2020 at 1:42 pm
  
  Touq
  Subscriber
  
  Many thanks for your replies.Dear Karthik, I have been trying to register in ANSYS customer portal to access the links you put in your reply but I could not because I'm a student. Can you please provide another link which can be accessed without registering in ANSYS customer portal.
- December 22, 2020 at 3:40 pm
  
  Karthik Remella
  Administrator
  
  Hi Array nYou should be able to access these links by following the instructions listed in this post.n nYou should be able to access these links by following the instructions listed in this post.nThank you. nKarthikn
- January 4, 2021 at 7:06 pm
  
  Touq
  Subscriber
  
  I could not access the links you provided using ANSYS 17.1 and 18.1. So, I had to wait until the Christmas holidays finished to solve some IT issues to install ANSYS 19.1 and now I'm able to access these links.After reading the links along with the fluent user's guide manual, the definition of a new transport equation can be by setting the parameters for the unsteady, convection, diffusion and source terms. To do that, a single UDF file should be written and contains the following DEFINE_DIFFUSIVITY, DEFINE_UDS_FLUX, DEFINE_UDS_UNSTEADY and DEFINE_SOURCE. Is this right or there are some other techniques?Also, I read in some forums that the UDS equation is laminar by default which means I have to include the turbulence effects in the diffusion term. Is this right? Thank you.n
- January 20, 2021 at 3:03 pm
  
  Karthik Remella
  Administrator
  
  Hello,nYou don't have to use UDFs if you are not modifying your transport equations. If you wish to modify your transport equations or define an anisotropic diffusivity, then you will need to use the UDF macros you mentioned in your post. nOtherwise, you can simply use the UDS equation as it is. Please read through the links to understand the equation on what effects are included and what are not. nI hope this helps.nThank you.nKarthikn