

February 9, 2021 at 9:55 amJack5864SubscriberHi there,nnI'm running a fluent simulation where the transport equations for my 2 UDS variables are highly coupled. The UDS diffusivity for the first is proportional to the value of the second, and the mass flux term for the second has a term proportional to the gradient of the first. This results in a highly coupled system of differential equations, which will not solve at the moment. Instead, the solution very quickly diverges.I was wondering if anyone had any advice on how to go about improving the stability of the solution.Thanks,nJackn

February 9, 2021 at 5:21 pmSurya DebAnsys EmployeeHello, nAre you using a Coupled PT solver? nDo you solve the UDS and the flow variables simultaneously? If the UDS properties are not tightly coupled to the flow, then can you converge the flow field first, then freeze the flow and solve for the UDS?nWhat discretization schemes are you using?.Regards,nSuryan

February 10, 2021 at 10:16 amJack5864SubscriberHi Surya,nnThanks for your message. The flow profile is relatively simple, so I use a SIMPLE solver for the pressurevelocity coupling. I also do as you mentioned, solving the flow first and then the UDS equations. The problem is that the UDS equations are tightly coupled together I believe. nThe discretization schemes I use are Secondorder Upwind for my UDS variablesnnThanks,nJackn

February 10, 2021 at 2:12 pmRobAnsys EmployeeHave you coded in stability terms for the two UDS equations? You might need to relax the relationship to improve the stability. n

February 10, 2021 at 2:59 pmJack5864SubscriberI haven't coded that no, how would I go about doing that?n

February 10, 2021 at 3:10 pmRobAnsys EmployeeCarefully! Simply you need to reduce how much you change each value each time in much the same way we do in the main solver: how is far more complicated. n

February 10, 2021 at 10:07 pmYasserSelimaSubscriberYou basically need to run a solver inside Fluent solver!! Good luck with thatnGoogle github CFD C++ code ... you might find a CFD code with 2D solver and you use it as starting point. n

February 12, 2021 at 10:18 amJack5864SubscriberThank you both,nnI'll do some digging to see what I can find!n

April 2, 2021 at 1:37 amZhangmin004Subscriber
Hi there,I'm running a fluent simulation where the transport equations for my 2 UDS variables are highly coupled. The UDS diffusivity for the first is proportional to the value of the second, and the mass flux term for the second has a term proportional to the gradient of the first. This results in a highly coupled system of differential equations, which will not solve at the moment. Instead, the solution very quickly diverges. I was wondering if anyone had any advice on how to go about improving the stability of the solution. Thanks,Jackhttps://forum.ansys.com/discussion/24336/highlycoupledudstransportequations
Dear Jack,nI just encounter the same problem as yours. Have you solved it?nI do not find out the coupling solution method for coupled UDSs in Fluent. I will really appreciate if you could tell me any advice about this problem?.Best regards,nMinn

 You must be logged in to reply to this topic.
Boost Ansys Fluent Simulations with AWS
Computational Fluid Dynamics (CFD) helps engineers design products in which the flow of fluid components is a significant challenge. These different use cases often require large complex models to solve on a traditional workstation. Click here to join this event to learn how to leverage Ansys Fluids on the cloud, thanks to Ansys Gateway powered by AWS.
Earth Rescue – An Ansys Online Series
The climate crisis is here. But so is the human ingenuity to fight it. Earth Rescue reveals what visionary companies are doing today to engineer radical new ideas in the fight against climate change. Click here to watch the first episode.
Ansys Blog
Subscribe to the Ansys Blog to get great new content about the power of simulation delivered right to your email on a weekly basis. With content from Ansys experts, partners and customers you will learn about product development advances, thought leadership and trends and tips to better use Ansys tools. Sign up here.
 Suppress Fluent to open with GUI while performing in journal file
 Floating point exception in Fluent
 What are the differences between CFX and Fluent?
 Heat transfer coefficient
 Getting graph and tabular data from result in workbench mechanical
 The solver failed with a nonzero exit code of : 2
 Difference between Kepsilon and Komega Turbulence Model
 Time Step Size and Courant Number
 Mesh Interfaces in ANSYS FLUENT
 error: Received signal SIGSEGV

5162

3257

2443

1308

956
© 2023 Copyright ANSYS, Inc. All rights reserved.