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large eddy simulation(LES) for turbomachinary

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Old   March 7, 2017, 03:28
Question large eddy simulation(LES) for turbomachinary
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FeiTeng
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Hi all
I have a question for using LES in a turbomachinary. Normally, we impose "Total Pressure","Total Temprature" and "Flow Angle" as inlet boundary conditions (subsonic). So , if I impose these as inlet boundary conditions, how could I impose velocity fluctuations at inlet ?
May I give some fluctuations on Total Pressure or Total Temprature ?? Can anyone gime me the answer or some recommendation?
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Old   March 7, 2017, 09:35
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Uwe Pilz
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An easy to implement an obvious way ist to calculate small timesteps and modify the U file in the latestTime dir. Your controldict.startFrom should contain "latestTime".
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Old   March 13, 2017, 01:17
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Quote:
Originally Posted by piu58 View Post
An easy to implement an obvious way ist to calculate small timesteps and modify the U file in the latestTime dir. Your controldict.startFrom should contain "latestTime".
Thank you for your answers ! But sorry, I don't quite understand. Could you please make it clear?
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Old   March 13, 2017, 01:38
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If you start the simulation you have to give initial values for U and p in the 0 directory. After running the simulation for a simulated time you get results in a directory which is named by the simulated time. This contains p and U.
If you change the values to the ones you want to haveand restart the simulation, these values will be used from this simulated time on.
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Old   March 13, 2017, 08:13
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I agree with PIU58 the problem with LES are the boundary and initial conditions. For subsonic flows you can specify velocities at the inlet, why don't tu work with velocities instead ? Nonetheless, you can follow PIU58 recommendations.
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Old   March 15, 2017, 20:41
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Thank you ! I will try it.
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Old   March 15, 2017, 20:57
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Sorry for late reply. In my simulation, the flow is transonic. I want to use LES method, and compare the result with the experimental data. But in the experiment, the total pressure,total temprature,and flow angle are specified at the inlet. How should I specify the inlet velocities instead ?
I can find the Mach Number distribution at the inlet from the experimental data. Can I get the velocity and static pressure distributions by using isentropic relations ?
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Old   March 16, 2017, 01:08
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> in the experiment, the total pressure,total temprature,and flow angle are specified at the inlet.

In this case you define the pressure at the inlet and the outlet (probably 0 there). For the velocity you give the gradient: zero gradient at the outlet and the gradient according to your inflow angle for the inlet.
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