

October 15, 2020 at 12:14 pmOliver_PaulickSubscriber
I want to simulate a flow in a cavity and evaluate the heat transfer coefficient at the wall (steady state simulation, fixed temperature at the wall). I am using ANSYS CFX 19.2
To make sure, that i have reached a steady state, i want to monitor the local wall heat flux durig the runtime on a few selected points. Unfortunally, the wall heat flux is not available in CFX Pre, so i cant use it as monitor point.
I assume, that CFX Post calculates the wall heat flux out of the basic items from the solver of the last iteration.
My idea was to create in CFX Pre an expression to replicate the wall heat flux from CFX Post, so that i can choose this expression as a monitor point in the solver.
I used the ANSYS documentation "CFX Solver Theory Guide  2.8.1 Mathematical Formulation". In the Setup, I selected automatic wall treatment, i used the formulas shown below to calculate the wall heat flux manually. Unfortunally, my solution deviates from the evaluation of the wall heat flux in CFX Post.
My questions ist: Why can I not calculate the "correct" wall heat flux q_w?
Do I use the wrong formulas, or do i evaluate the needed items (such as heat capacity, conductivity, turb. kinetic energy, viscosity, density) at the wrong locations?
My current approach is:
I evaluate heat capacity, conductivity, turb. kinetic energy, viscosity, density at the center of the wall adjacent element, at Wall Distance = s/2 (thickness of first element layer s is known)
I evaluate T_f directly at the Wall (Wall distance = 0)
T_W is the fixed Temperature of the Boundary (Also Wall distance = 0)
Delta U = ([email protected] Distance = s)  ([email protected] Distance = 0)
I calculate q_w with the formulas shown below. Next, i compare it to the evaluation of q_w in the same wall adjacent cell in CFX Post
Do you have any clues or hibts to solve my problem?
Thank you for your help in advance!
Beste regards
Oliver

October 15, 2020 at 1:14 pmDrAmineAnsys EmployeeI did not read the whole message as I stopped as you wrote you can not monitor the heat flux. You can monitor that in Solver: You define an expression where you area integrate the wall heat flux. In the Out file you can check the values of heat fluxes at the end of the outfile too.n

 You must be logged in to reply to this topic.
Simulation World 2022
Check out more than 70 different sessions now available on demand. Get inspired as you hear from visionary companies, leading researchers and educators from around the globe on a variety of topics from lifesaving improvements in healthcare, to bold new realities of space travel. Take a leap of certainty and check out a session today here.
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
 Heat transfer coefficient
 What are the differences between CFX and Fluent?
 Floating point exception in Fluent
 The solver failed with a nonzero exit code of : 2
 Difference between Kepsilon and Komega Turbulence Model
 Getting graph and tabular data from result in workbench mechanical
 Time Step Size and Courant Number
 Mesh Interfaces in ANSYS FLUENT
 error in cfd post

1932

1708

925

688

378
© 2022 Copyright ANSYS, Inc. All rights reserved.