random velocity fluctuation udf

sunny89 · January 30, 2014, 01:43

Hello, I want to give randomly varying (temporal) velocity (about a mean value) as inlet boundary condition. Which function do I have to use in UDF and how can I set the range ??

Komon · March 12, 2014, 13:12

hey,

sorry for this not being an answer to your question but rather a new question. I have a similar problem to yours. But instead of putting velocity fluctuations on the inlet I'd like to impose them on whole domain. Namely, I'm trying to run LES simulation of a periodic channel flow with which I'd like to get results for turbulent inflow that will be used in other simulations. I've noticed that there are some simulations that impose fluctuations on the mean velocity profile in whole domain (namely Lund et al, 1998 mentions this)...but I haven't noticed that they use periodic bc (again, Lund uses semi implicit periodic conditions). Neither have I seen how these fluctuations are described. The only recommendation I got was to use 10% amplitude of mean velocity. So I'd like to ask if anyone can give some advice/further info on my intention-is it ok to make such simulations, what kind of fluctuations should I use....basically what to look for.

As for the moment, I'll try to initialize simulations with some sort of sinusoidal velocity in the domain....and I'll see what comes out.

thanks for the answers and all the best

January 30, 2014, 01:43	random velocity fluctuation udf	#1
sunny89 New Member Join Date: Jan 2014 Posts: 1 Rep Power: 0	Hello, I want to give randomly varying (temporal) velocity (about a mean value) as inlet boundary condition. Which function do I have to use in UDF and how can I set the range ??

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March 12, 2014, 13:12		#2
Komon Member Join Date: Sep 2011 Posts: 43 Rep Power: 14	hey, sorry for this not being an answer to your question but rather a new question. I have a similar problem to yours. But instead of putting velocity fluctuations on the inlet I'd like to impose them on whole domain. Namely, I'm trying to run LES simulation of a periodic channel flow with which I'd like to get results for turbulent inflow that will be used in other simulations. I've noticed that there are some simulations that impose fluctuations on the mean velocity profile in whole domain (namely Lund et al, 1998 mentions this)...but I haven't noticed that they use periodic bc (again, Lund uses semi implicit periodic conditions). Neither have I seen how these fluctuations are described. The only recommendation I got was to use 10% amplitude of mean velocity. So I'd like to ask if anyone can give some advice/further info on my intention-is it ok to make such simulations, what kind of fluctuations should I use....basically what to look for. As for the moment, I'll try to initialize simulations with some sort of sinusoidal velocity in the domain....and I'll see what comes out. thanks for the answers and all the best