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What are Padé-type filter and low pass filter in CFD?

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Old   November 15, 2016, 10:53
Default What are Padé-type filter and low pass filter in CFD?
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carl jung
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Hi all,

I was reading a Garmann and Visbal's paper, Dynamics of revolving wings for various aspect(J. Fluid Mech, 2014), but couldn't understand how they worked with the grids.

Their case is about a single rotating plate in a Cartesian frame. As the wing rotates, the Cartesian frame rotates together with the wing. I have attached a their figure about it. They said "For all revolving wing simulations presented in this work, the entire mesh is moved in a rigid fashion using the prescribed kinematics."

I also have data in a fixed Cartesian frame, so I want to rotate the flow data like they did. But I don't understand most of methods they used such as Padé-type filter, Higher order Low-pass filter. I have no idea how the filters are used numerical calculation in CFD. I'm actually not even sure if those were used for the rotation of Cartesian frame.

Any comments, opinions, replies would be appreciated.

Thank you,

Carl
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Old   November 15, 2016, 11:27
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Filippo Maria Denaro
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Originally Posted by carl jung View Post
Hi all,

I was reading a Garmann and Visbal's paper, Dynamics of revolving wings for various aspect(J. Fluid Mech, 2014), but couldn't understand how they worked with the grids.

Their case is about a single rotating plate in a Cartesian frame. As the wing rotates, the Cartesian frame rotates together with the wing. I have attached a their figure about it. They said "For all revolving wing simulations presented in this work, the entire mesh is moved in a rigid fashion using the prescribed kinematics."

I also have data in a fixed Cartesian frame, so I want to rotate the flow data like they did. But I don't understand most of methods they used such as Padé-type filter, Higher order Low-pass filter. I have no idea how the filters are used numerical calculation in CFD. I'm actually not even sure if those were used for the rotation of Cartesian frame.

Any comments, opinions, replies would be appreciated.

Thank you,

Carl

The name of filtering in that paper is taken from the LES nomenclature. They apply a filtering procedure on the field, that is a way to eliminate wavenumber components of the solution higher than a certain threshold. However, from what I read, they do not perform a true LES with an explicit SGS model but let that the truncation error of the scheme act as model (ILES). I suggest to read the paper of Lele (1992).
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Old   November 15, 2016, 11:45
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Originally Posted by FMDenaro View Post
The name of filtering in that paper is taken from the LES nomenclature. They apply a filtering procedure on the field, that is a way to eliminate wavenumber components of the solution higher than a certain threshold. However, from what I read, they do not perform a true LES with an explicit SGS model but let that the truncation error of the scheme act as model (ILES). I suggest to read the paper of Lele (1992).
Thank you, Filippo. I understood it wrong before. However, I guess Pade filter is not what I want for now. My main focus is the rotating the mesh using some transformation which satisfies geometric conservation law.

Do you have an idea how they rotated the Cartesian frame? I've never learned things like before
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Old   November 15, 2016, 12:02
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Originally Posted by carl jung View Post
Thank you, Filippo. I understood it wrong before. However, I guess Pade filter is not what I want for now. My main focus is the rotating the mesh using some transformation which satisfies geometric conservation law.

Do you have an idea how they rotated the Cartesian frame? I've never learned things like before
I never worked on such problem and I cannot give you my idea without thinking about carefully...
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Old   November 15, 2016, 12:06
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I never worked on such problem and I cannot give you my idea without thinking about carefully...
That's fine. I appreciate your replies!
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cartesian grid, low pass filter, padé-type filter, revolving wing, rotation

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