February 8, 2023 at 2:42 pmBenjamin WalzSubscriber
I am trying to simulate the indoor air flow inside a room model.
More specifically, I want to calculate thermal comfort indices according to ISO 7730 (PMV, PPD and Draught rate).
How do I determine the local turbulent intensity or the variation of the air velocity, which I need to calculate the draught rate?
Is there an already existing UDF that I can use for that? Unfortunaely, I am not used to write C-Code.
Any help regarding this topic would be greatly appreciated.
February 9, 2023 at 10:29 amRobAnsys Employee
It's the local velocity, so velocity magnitude that's used. You may also want to account for solar gain (heating) as that's a significant part of comfort.
Yes, there is a UDF, but as you'll know from reading the rules when you signed up I (as Ansys staff) can't share it on here. You may want to have a look on the Customer Portal; students may not have access but staff may if your site has a maintained licence.
February 10, 2023 at 7:49 amBenjamin WalzSubscriber
Hi Rob, thank you for your answer.
My current model does not take solar radiation (eg through a window) into account. I will model solar radiation in a later step.
The local velocity of air is used to calculate the PMV, but as far as I know, for the Draught rate I need a measure for local turbulence. I am slightly confused with the terminology here, since in german there is something called "Turbulenzgrad", which translates approximately to "turbulence intensity". Its defined locally as follows:
TU = 100 * standart deviation of velocity / mean velocity [%] This is how i measure turbulence in the laboratory. The measurements are used to "calibrate" my CFD-Model.
I found following equation in Fluent theory guide:
Tu = 100/u *(k*2/3)^0.5 ,unit is also % i guess.
Do these two expressions describe the same?
I do have access to the customer portal, I couldnt find something on this in Solutions. Can I ask for a hint where exactely to look for such a udf?
February 10, 2023 at 10:55 amRobAnsys Employee
I searched for PMV but I also have a staff level view so it may be slightly different. In the UDF I have I can't see any turbulence model values.
In the equation, you've got "k" rather than standard deviation of velocity, so you'll need to check the model definitions: the Theory Guide is fairly comprehensive.
- 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.
- 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 non-zero exit code of : 2
- Difference between K-epsilon and K-omega Turbulence Model
- Time Step Size and Courant Number
- Mesh Interfaces in ANSYS FLUENT
- error in cfd post
© 2023 Copyright ANSYS, Inc. All rights reserved.