The diagnostic plot - a new way to appraise turbulent boundary-layer data

It has been shown that the diagnostic plot may distinguish between accurately measured data in the near-wall region and data which may suffer from various problems. The diagnostic plot also has the interesting property that both the inner (y+ < 10) and outer regions can be made to collapse in the same plot. There is unfortunately not yet enough well-resolved data of u! for high Reynolds numbers to clarify how u! scales in the outer region although in Ref. [1] scaling with U# gives the smallest scatter when plotted against the wall distance normalized with the boundary-layer thickness. When better data becomes available it will be interesting to see how the diagnostic plot varies with Re in the outer region. If the Reynolds number variation is small the diagnostic plot may be used to estimate the boundary-layer free-stream velocity from a few measurement points in the outer region of u! and U, which may be helpful when studying atmospheric boundary layers.