Contributions of very low wavenumbers to wall pressure and wall shear stress in high Reynolds number zero pressure gradient turbulent boundary layers.*

Wall-bounded flows are ubiquitous in industrial applications (e.g., over aircraft wings and submarines) and affect vehicle performance through the resulting fluctuations in wall shear stress (associated with skin-friction drag) and wall pressure (linked to flow-induced vibrations). Subconvective wavenumber contributions to wall pressure and shear stress serve as crucial inputs to noise and vibration models; the scaling of these contributions relies on extrapolation from low Reynolds number measurements. However, it is known that wall turbulence is altered at high Reynolds numbers by the emergence and increasing energetic content of "very large-scale motions". 

This experimental collaboration, composed of members from Stanford University, Princeton University, and the University of Melbourne, aims to understand the contribution of very low wavenumbers to wall pressure and shear stress at high Reynolds numbers. The data sets resulting from this collaboration are simultaneously acquired large-field velocity data from PIV and arrays of wall-pressure and wall-shear stress sensors (which allow for a direct measurement) in two unique experimental facilities: the High-Pressure Wind Tunnel at Stanford University and the HRNBLWT wind tunnel at the University of Melbourne. These wind tunnels have complementary capabilities, overlapping low Mach numbers (M < 0.02), and a maximum Reynolds number of Re_τ  = 15 x 10³. Preliminary results on wall pressure, wall shear stress, and PIV/PTV will be discussed.