Rotation of the velocity measurements
The measurement frame of reference varies between set-ups. In some instances, the instrument has an axis aligned with the direction of flow, which is ideal to account for the varying levels of anisotropy amongst components [1][2]. Still, it's possible to rotate the measurements into the main component of the flow if intending on making use of the different components when estimating [math]\displaystyle{ \varepsilon }[/math] or other turbulence quantities (e.g., Reynold stresses). If one intends on using only the vertical velocity component to estimate [math]\displaystyle{ \varepsilon }[/math], then this step of rotating the velocity measurements may be skipped. However, anisotropic velocity spectra caused when the largest turbulence scales are less than XX times the Kolmogorov length scale, may inhibit using the vertical velocity component to derive [math]\displaystyle{ \varepsilon }[/math]. In these situations, it may be possible to use the longitudinal velocity component. The L&O methods paper by Bluteau et al (2011)[2], discusses this topic in greater detail.
Methods used for rotating into the analysis frame of reference
We will update when our final recommendation is set in stone. Also, comment about large vertical velocities on sloped bottoms...
- Using time-averaged velocities in each segment
- Principal component analysis
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
- ↑ 2.0 2.1 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
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