September 6, 2023 at 3:21 pmT-Ying LinSubscriber
Following with a well documented paper to try and benchmark my work. Was able to get comparable results for low Ra number models but when I tried to do the same for a high Ra number case (10^9), the heat transfer coefficient produced was significantly higher than expected. I'm modeling the natural convection of a concentric horizontal cylindrical annuli with the boundary conditions seen here in this diagram. The energy balances out, I'm using a similar mesh and monitoring the temperature, velocity, and pressure to see when the model converges. I'm honestly at a loss as to why it's so much higher. Any help would be appreciated!
September 8, 2023 at 6:43 amC NAnsys Employee
Hello T-Ying Lin,
Reasons for getting higher convective heat transfer coefficient are as follows
1) It is known fact that rayleigh number is a product of grashoff number and prandtl number where if the value goes beyond 10^9 the flows becomes turbulent .
2)The Heat transfer coefficient parameter is the property that combines the fluid flow and solid geometry.
3)The convective heat transfer coefficient for turbulent flow is higher because it has thinner stagnant fluid flim layer on the surface than the laminar flow and also increases with wall roughness as reynolds number increases and the viscous sub layer becomes thin.
4)The turbulent flow generate more momentum and eddies due to the higher entrophy (randomness of molecules)- this contributes to more velocity component less viscous resistance . So heat dissipation happens quickly.
The Ansys treats this problem as turbulent flow which is different from the laminar flow mechanics.
I am attaching the user guide link for some best practices guide lines for setting up high rayleigh number flow cases
7.3. Operating Conditions (ansys.com) In this link refer
184.108.40.206.1. Guidelines for Solving High-Rayleigh-Number Flows
I hope this helps you in getting the results correctly for your high rayleigh number flow case.
- 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.
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.
- Floating point exception in Fluent
- What are the differences between CFX and Fluent?
- Heat transfer coefficient
- Difference between K-epsilon and K-omega Turbulence Model
- Getting graph and tabular data from result in workbench mechanical
- The solver failed with a non-zero exit code of : 2
- Suppress Fluent to open with GUI while performing in journal file
- Mesh Interfaces in ANSYS FLUENT
- Time Step Size and Courant Number
- error: Received signal SIGSEGV
© 2023 Copyright ANSYS, Inc. All rights reserved.