ZFLES/SBES with synthetic turbulence

Pete12 · July 31, 2018, 10:25

Hi. I am trying to setup a hybrid LES/RANS simulation and facing some problems.

I want to generate synthetic turbulence at the inlet of my domain since i just have stationary data which i got from my experiments and upstream RANS simulations. Ansys does have the harmonic flow generator for creating synthetic turbulence at predefined RANS/LES Interfaces when you are using ZFLES. First i wanted to use the SBES-Model but i can not find the option for activating the harmonic flow generator without using ZFLES. Since ZFLES also uses a hybrid technice called WMLES i am considering to use it now.

Now to my questions:

1. How do i use SBES together with the harmonic flow generator?

2. Can i define my whole domain as LES Zone when i am using the ZFLES-Methode and use my stationary data as inlet condition? Then the harmonic flow generator should use this data to create synthetic turbulence.

3. Are there any other options in CFX to create synthetic turbulence with stationary data profiles?

I hope you can give me some hints. Thanks for the answers.

Pete12 · August 2, 2018, 05:53

Perhaps my questions were a bit confusing.

All i want to implement is synthetic turbulence at the inlet of my Scale Resolving Simulation in CFX. I am simulating an u-shaped pipe flow and according to "Best Practice: Scale-Resolving Simulations in ANSYS CFD" by Menter i would assign my case to the stable flows. Without synthetic turbulence SAS or other methods might not change into LES mode.

All i was able to find is the paper "Scale-Adaptive Simulation with Artificial Forcing" by Menter but even he is using ANSYS Fluent although the Ansys help refers to the named paper.

In Ansys fluent i would be able to use the Vortex Method or the Spectral Synthesizer for e.g DES. Is there no similar option for CFX?

ghorrocks · August 2, 2018, 08:06

No I understood your question perfectly. It is just a very specialised and technical topic which not many people will know the answer to. I don't know the answer so kept quiet.

I suspect ANSYS Support has some information along these lines. I would contact them.

Pete12 · August 2, 2018, 09:41

Seems to be the last option. Gonna try it. Thanks.

Lance · August 3, 2018, 02:44

Quote:

Originally Posted by Pete12

Seems to be the last option. Gonna try it. Thanks.

I asked the support the same question many years ago. Their response then was to implement a user defined function with added fluctuations (from a .csv file). Not really elegant or - in my case - accurate. If there are hidden features in newer versions of CFX please let us know

MikeBravo · January 19, 2019, 19:27

Hi Pete12,
Not sure if you ever got your answer, but at least for posterity:

Synthetic turbulence and SBES don't go together. SBES is a hybrid model already, you can specify profiles of RANS turbulence intensity and length scale or viscosity ratio at your inlet. When the SBES shielding function determines it is time to switch to LES, it converts the unresolved RANS TKE into coherent turbulence automatically. Very user friendly!

July 31, 2018, 10:25	ZFLES/SBES with synthetic turbulence	#1
Pete12 New Member Join Date: Jul 2018 Posts: 3 Rep Power: 8	Hi. I am trying to setup a hybrid LES/RANS simulation and facing some problems. I want to generate synthetic turbulence at the inlet of my domain since i just have stationary data which i got from my experiments and upstream RANS simulations. Ansys does have the harmonic flow generator for creating synthetic turbulence at predefined RANS/LES Interfaces when you are using ZFLES. First i wanted to use the SBES-Model but i can not find the option for activating the harmonic flow generator without using ZFLES. Since ZFLES also uses a hybrid technice called WMLES i am considering to use it now. Now to my questions: 1. How do i use SBES together with the harmonic flow generator? 2. Can i define my whole domain as LES Zone when i am using the ZFLES-Methode and use my stationary data as inlet condition? Then the harmonic flow generator should use this data to create synthetic turbulence. 3. Are there any other options in CFX to create synthetic turbulence with stationary data profiles? I hope you can give me some hints. Thanks for the answers.

August 2, 2018, 08:06		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	No I understood your question perfectly. It is just a very specialised and technical topic which not many people will know the answer to. I don't know the answer so kept quiet. I suspect ANSYS Support has some information along these lines. I would contact them. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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August 2, 2018, 05:53		#2
Pete12 New Member Join Date: Jul 2018 Posts: 3 Rep Power: 8	Perhaps my questions were a bit confusing. All i want to implement is synthetic turbulence at the inlet of my Scale Resolving Simulation in CFX. I am simulating an u-shaped pipe flow and according to "Best Practice: Scale-Resolving Simulations in ANSYS CFD" by Menter i would assign my case to the stable flows. Without synthetic turbulence SAS or other methods might not change into LES mode. All i was able to find is the paper "Scale-Adaptive Simulation with Artificial Forcing" by Menter but even he is using ANSYS Fluent although the Ansys help refers to the named paper. In Ansys fluent i would be able to use the Vortex Method or the Spectral Synthesizer for e.g DES. Is there no similar option for CFX?

August 2, 2018, 09:41		#4
Pete12 New Member Join Date: Jul 2018 Posts: 3 Rep Power: 8	Seems to be the last option. Gonna try it. Thanks.

January 19, 2019, 19:27		#6
MikeBravo New Member Mike Join Date: Jan 2018 Posts: 29 Blog Entries: 6 Rep Power: 8	Hi Pete12, Not sure if you ever got your answer, but at least for posterity: Synthetic turbulence and SBES don't go together. SBES is a hybrid model already, you can specify profiles of RANS turbulence intensity and length scale or viscosity ratio at your inlet. When the SBES shielding function determines it is time to switch to LES, it converts the unresolved RANS TKE into coherent turbulence automatically. Very user friendly!