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. 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. Mention anisotropy, and refer to my own paper

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