CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

steady vs. unsteady flow at the wall

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   November 11, 2020, 11:37
Default steady vs. unsteady flow at the wall
  #1
New Member
 
Tyler Richardson
Join Date: Jun 2017
Posts: 26
Rep Power: 5
tricha122 is on a distinguished road
Hi,

(note below concerns incompressible flows only)

I have been using a UDF to calculate the HTC at the wall for a steady solution fairly repeatably for a while now.

I now have a situation where i have a rotating mesh interfacing with a static mesh (both fluid) and so i now need to run unsteady. I noticed when i ran unsteady my HTCs seemed off by quite a bit from what i expected (about 4-5x off).

I then simplified the situation and ran just a simple cylinder pseudo-transient (ramping up flow rate, then holding until convergence) and unsteady (ramping up flow rate, and then holding until convergence).

The HTC i calculate on the pseudo-transient run is as expected. The HTC i calculate on the unsteady run is ~4-5x less than expected.

The velocity profiles (when i plot them on a line/rake) look the same.

the crux of the HTC calc comes down to the calculation of y*, which ultimately relies on the turbulent kinetic energy, kp = C_K(c0,t0)

Is there any reason why i would expect kp to be different in an unsteady solution vs. a pseudo-transient solution?

I have suspected that perhaps my solution wasnt fully converged so i ran it for many more iterations, ive switched to second order for momentum, k, epsilon, etc... no dice

Anyone have any idea on what to check to try and close this gap?

Alternatively i could run the unsteady solution for X iterations, then run a steady solution, and do this back and forth to get the information that i am looking for... is it possible to do this? Will the "steady" solution run in the instantaneous position of the rotating mesh after i iterations?

Any help would be greatly appreciated

Thanks!
tricha122 is offline   Reply With Quote

Reply

Tags
htc, incompressible, udf, unsteady

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Unsteady Restart Divergence pro_ SU2 6 May 20, 2020 16:17
Version13 & Version 15 : unsteady DPM with steady Flow souria FLUENT 4 October 10, 2014 10:23
Radiation interface hinca CFX 15 January 26, 2014 18:11
how to stimulate unsteady flow to steady using fan kelbros Phoenics 4 December 12, 2013 04:50
Unsteady AND Steady mode for Fully Developped Flow Dominique FLUENT 5 April 16, 2004 18:58


All times are GMT -4. The time now is 18:35.