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Usage of Lambda2 criterion??

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Old   May 15, 2017, 08:17
Default Usage of Lambda2 criterion??
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vidyadhar
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Hello All,

I want to visualize the vortex structures in the flow through a pipe junction having square cross-section.

I used the Lambda2<0 criterion.

After execution of this command in terminal, for certain time steps, it is displaying :
From function eigenValues(const tensor&)
in file core/primitives/Tensor/tensor/tensor.cpp at line 164
complex eigenvalues detected for tensor: (0.2251204266 1.082743573e-10 -0.00015966764 1.082743573e-10 0.225120397 8.240372463e-07 -0.00015966764 8.240372463e-07 0.9004717292)
Writing -Lambda2

1. Can anyone let me know what does this mean?

When I tried to take the contours of Lambda2, in paraview, it is showing a range of values from negative to positive through zero.
2. Can anyone please explain why the range contains positive values too!

By definition, Lambda2 should be negative so that it contains vortex cores?
3. So, which value of Lambda2 should I select, so as to contain the vortex cores? Negative or positive?

Thanks in advance!!!
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Old   December 1, 2019, 23:14
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Jianrui Zeng
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Quote:
Originally Posted by vidyadhar View Post
Hello All,

I want to visualize the vortex structures in the flow through a pipe junction having square cross-section.

I used the Lambda2<0 criterion.

After execution of this command in terminal, for certain time steps, it is displaying :
From function eigenValues(const tensor&)
in file core/primitives/Tensor/tensor/tensor.cpp at line 164
complex eigenvalues detected for tensor: (0.2251204266 1.082743573e-10 -0.00015966764 1.082743573e-10 0.225120397 8.240372463e-07 -0.00015966764 8.240372463e-07 0.9004717292)
Writing -Lambda2

1. Can anyone let me know what does this mean?

When I tried to take the contours of Lambda2, in paraview, it is showing a range of values from negative to positive through zero.
2. Can anyone please explain why the range contains positive values too!

By definition, Lambda2 should be negative so that it contains vortex cores?
3. So, which value of Lambda2 should I select, so as to contain the vortex cores? Negative or positive?

Thanks in advance!!!
Any idea about these questions?
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Old   December 9, 2019, 14:19
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Check out this wiki page -- it should answer your questions : https://en.wikipedia.org/wiki/Lambda2_method.

Caelan
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Old   July 6, 2020, 06:06
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Arash
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Quote:
Originally Posted by vidyadhar View Post
Hello All,

I want to visualize the vortex structures in the flow through a pipe junction having square cross-section.

I used the Lambda2<0 criterion.

After execution of this command in terminal, for certain time steps, it is displaying :
From function eigenValues(const tensor&)
in file core/primitives/Tensor/tensor/tensor.cpp at line 164
complex eigenvalues detected for tensor: (0.2251204266 1.082743573e-10 -0.00015966764 1.082743573e-10 0.225120397 8.240372463e-07 -0.00015966764 8.240372463e-07 0.9004717292)
Writing -Lambda2

1. Can anyone let me know what does this mean?

When I tried to take the contours of Lambda2, in paraview, it is showing a range of values from negative to positive through zero.
2. Can anyone please explain why the range contains positive values too!

By definition, Lambda2 should be negative so that it contains vortex cores?
3. So, which value of Lambda2 should I select, so as to contain the vortex cores? Negative or positive?

Thanks in advance!!!
This might be useful for your third question.
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