Rotation of the velocity measurements: Difference between revisions
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To estimate <math>\varepsilon</math> from all the different velocity components, the measurements must be rotated into the main direction of the flow. In some instances, the instrument's [[frame of reference]] may be aligned with the direction of flow, which is ideal to account for the varying levels of [[Velocity inertial subrange model#anisotropy|anisotropy]] amongst components <ref name="Gargett.etal1984">{{Cite journal | |||
|authors= A. E. Gargett, T. R. Osborn, and P.W. Nasmyth | |||
|journal_or_publisher= J. Fluid. Mech. | |||
|paper_or_booktitle= Local isotropy and the decay of turbulence in a stratified fluid | |||
|year= 1984 | |||
|doi=10.1017/S0022112084001592 | |||
}}</ref><ref name="Bluteau.etal2011">{{Cite journal | |||
|authors= C.E. Bluteau, N.L. Jones, and G. Ivey | |||
|journal_or_publisher= Limnol. Oceanogr.: Methods | |||
|paper_or_booktitle= Estimating turbulent kinetic energy dissipation using the inertial subrange method in environmental flows | |||
|year= 2011 | |||
|doi=10:4319/lom.2011.9.302 | |||
}}</ref>. If this isn't the case, then the velocities' measurement frame must be rotated into that of the flow, which we refer to as the analysis frame of reference. | |||
= Methods used for rotating into the analysis frame of reference= | |||
* Using time-averaged velocities in each segment | * Using time-averaged velocities in each segment | ||
* Principal component analysis | * Principal component analysis | ||
==Recommendations== | |||
{{FontColor|fg=white|bg=red|text=We will update when our final recommendation is set in stone. Also, comment about large vertical velocities on sloped bottoms... The page is too wordy}} | |||
If one intends on using only the vertical velocity component to estimate <math>\varepsilon</math>, then the rotation of the velocity measurements into a new frame of reference may be skipped. The analysis frame of reference is thus the same as the measurement frame provided one direction is aligned with gravity. | |||
{{FontColor|fg=white|bg=red|text=If not, then which strategy is best ? I think all are OK}} | |||
==References== | |||
<references /> | |||
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Return to [[Preparing quality-controlled velocities]] | |||
Latest revision as of 18:54, 5 July 2022
To estimate [math]\displaystyle{ \varepsilon }[/math] from all the different velocity components, the measurements must be rotated into the main direction of the flow. In some instances, the instrument's frame of reference may be aligned with the direction of flow, which is ideal to account for the varying levels of anisotropy amongst components [1][2]. If this isn't the case, then the velocities' measurement frame must be rotated into that of the flow, which we refer to as the analysis frame of reference.
Methods used for rotating into the analysis frame of reference
- Using time-averaged velocities in each segment
- Principal component analysis
Recommendations
We will update when our final recommendation is set in stone. Also, comment about large vertical velocities on sloped bottoms... The page is too wordy
If one intends on using only the vertical velocity component to estimate [math]\displaystyle{ \varepsilon }[/math], then the rotation of the velocity measurements into a new frame of reference may be skipped. The analysis frame of reference is thus the same as the measurement frame provided one direction is aligned with gravity.
If not, then which strategy is best ? I think all are OK
References
- ↑ A. E. Gargett, T. R. Osborn and and P.W. Nasmyth. 1984. Local isotropy and the decay of turbulence in a stratified fluid. J. Fluid. Mech.. doi:10.1017/S0022112084001592
- ↑ C.E. Bluteau, N.L. Jones and and G. Ivey. 2011. Estimating turbulent kinetic energy dissipation using the inertial subrange method in environmental flows. Limnol. Oceanogr.: Methods. doi:10:4319/lom.2011.9.302
Return to Preparing quality-controlled velocities
