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Time-accurate preconditioning for LES/DNS of turbulent flows

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Old   May 31, 2013, 16:20
Default Time-accurate preconditioning for LES/DNS of turbulent flows
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Francesco Capuano
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Dear all,

I have some some questions and doubts regarding the use of compressible codes for solving low-Mach (order 0.01-0.1) turbulent flows (using LES or DNS).

The main question is the following: is it really necessary to use time-accurate preconditioning techniques (e.g. dual-time stepping) for turbulent computations?

Some LES codes do that, but some others simply use an explicit time-integration with small time-steps. I don't quite understand whether the use of preconditioning is a matter of time-step restriction, accuracy, or both. Any experience on that?

Thanks in advance.
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Old   May 31, 2013, 17:13
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Filippo Maria Denaro
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Quote:
Originally Posted by francesco_capuano View Post
Dear all,

I have some some questions and doubts regarding the use of compressible codes for solving low-Mach (order 0.01-0.1) turbulent flows (using LES or DNS).

The main question is the following: is it really necessary to use time-accurate preconditioning techniques (e.g. dual-time stepping) for turbulent computations?

Some LES codes do that, but some others simply use an explicit time-integration with small time-steps. I don't quite understand whether the use of preconditioning is a matter of time-step restriction, accuracy, or both. Any experience on that?

Thanks in advance.
Hi,
my opinion is that a pure compressible code could work at low Mach without preconditioning provided that the scheme is very accurate and the time step is constrained by the CFL condition based on the sound velocity.
Accuracy is important as also small errors in computing the density can result in high pressure perturbation.
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Old   May 31, 2013, 18:13
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We use explicit time integration (with proper CFL bounds) all the time for Ma=0.1 computations, both LES and DNS and haven't encountered any problems.
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