First sub-viscous resolution near-wall PIV measurements in high-Reynolds number turbulent pipe flows

Kurzfassung

Near-wall turbulence statistics at high Reynolds number remain difficult to measure because the relevant viscous scales become extremely small while long acquisition records are required for statistical convergence. In this work, we report high-speed, high-magnification profile ZIVmeasurementsintheCICLoPELongPipefacility, aimedatresolving the near-wall region of turbulent pipe flow with sub-viscous spatial resolution. Measurements were performed over the range 5,500 ≤ Re_tau < 45,500, corresponding to viscous length scales from approximately 82 µm down to 10 µm. The dataset provides statistically converged, two-component velocity measurements in a Reynolds-number range previously accessible mainly through single-point techniques. The streamwise velocity variance profiles show the expected near-wall inner peak and a systematic increase of its magnitude with Reynolds number. At lower Reynolds numbers, the results agree well with available DNS data, while the highest-Reynolds-number cases extend previous experimental evidence from CICLoPE. The observed trend is compatible with a slow, approximately logarithmic growth of the inner peak, although residual spatial-resolution effects remain detectable at the largest Reynolds numbers. Measurements of the wall-normal variance and Reynolds shear stress further demonstrate the capability of the present approach to provide simultaneous multi-component near-wall turbulence statistics in high-Reynolds-number pipe flow.