Hot-wire spatial resolution issues in adverse pressure gradient turbulent boundary layers.

The effect of a finite length of hot-wire probe sensor length on the measured streamwise velocity fluctuations is well understood in canonical wall-bounded flow, where the small-scale energy has been found to be universal and invariant with Reynolds number. A straightforward application of that assumption to non-canonical flows such as strong adverse pressure gradient (APG) flows has, however, been hampered since the effect of Re and APG could not conclusively be studied separately due to the lack of data with a clear scale separation. The present experimental investigation at R e τ ≈ 4000 in weak, moderate and strong APGs with different wire length shows that spatial averaging effects are not only limited to the inner layer. A note of caution is hence warranted for measurements that seemingly try to take the bias effect of spatial attenuation into account by performing measurements with albeit long but fixed viscous-scaled wire length. • Measurements of TBL with varying hot-wire length at high Re covering wide range of APG conditions. • Small-scale energy attenuation in hot-wire measurements not limited to inner layer in strong APG TBLs. • Hot-wire spatial averaging effects remain present for strong APG conditions even at high Re. • Contrary to other studies, small-scale energy remains important albeit small in outer layer. [ABSTRACT FROM AUTHOR]