Wall-pressure–velocity couplings in turbulent boundary layers spanning three orders of magnitude in Reynolds number*

Turbulent boundary layer pressure fluctuations on an aircraft fuselage or ship hull play a significant role in their design since such pressure disturbances can affect the structural integrity and passenger comfort. These wall-pressure fluctuations originate from the coherent motions coexisting in the overlying turbulent boundary layers, and the correlation between the two has been studied only in the low friction Reynolds number regime (Re_τ ~10³). For instance, Gibeau & Ghaemi (2021, JFM) and Deshpande et al. (2024, arXiv:2406.15733) show that the mid-frequency range (0.0014< f⁺ <0.012) of the wall-pressure fluctuations strongly correlate with intermediate-scaled Reynolds shear stress carrying motions, while those of the low-frequency range (f<0.0014) correlate with the large-scale motions. The wall-pressure power spectrum of these low Re_τ flows is, however, beset with limited scale separation and exhibits weak signatures at large scales; these large scales are well known to become statistically significant at very high Re_τ, relevant to flows over aircraft and ships. The present study addresses this knowledge gap through simultaneous measurements of wall pressure and velocity fluctuations at Re_τ~10⁶, taken from the near-neutral atmospheric surface layer forming over the salt playa of Utah's west desert. These large Re_τ results reveal that pressure-velocity correlations at low frequencies have significantly enhanced magnitudes relative to those at mid-frequencies.