The goal of this experimental study is to investigate the wall pressure wavenumberfrequency spectra induced by a turbulent boundary layer in the presence of a mean pressure gradient. The mean pressure gradient is achieved by changing the ceiling angle of a rectangular channel flow. Wall pressure spectra are measured for zero-, adverse-and favorablepressure-gradient boundary layers by using a pinhole microphone in conjunction with a high-frequency-calibration procedure. A linear antenna based on a non-uniform distribution of remote microphones mounted on a rotating disk is also developed to obtain a direct measurement of both aerodynamic and acoustic components of wavenumber-frequency spectra. First results, comparisons and analyses are then discussed. Nomenclature C ppressure coefficient h height of the channel H = δ 1 /δ θ shape factor k wavevector (k ∈ I R 3 ) p w wall pressure q 0 = ρU 2 0 /2 dynamic pressure Re δ 1 = U ∞ δ 1 /ν Reynolds number based on δ 1 Re + = u τ δ/ν Kármán or friction Reynolds number r separation vector (polar coordinates) R pp (r, ω) pressure cross spectral density S pp (ω) = R pp (r = 0, ω) one-sided wall pressure spectrum

The purpose of this work is to check if additive manufacturing technologies are suitable for reproducing porous samples designed for sound absorption. The work is an inter-laboratory test, in which the production of samples and their acoustic measurements are carried out independently by different laboratories, sharing only the same geometry codes describing agreed periodic cellular designs. Different additive manufacturing technologies and equipment are used to make samples. Although most of the results obtained from measurements performed on samples with the same cellular design are very close, it is shown that some discrepancies are due to shape and surface imperfections, or microporosity, induced by the manufacturing process. The proposed periodic cellular designs can be easily reproduced and are suitable for further benchmarking of additive manufacturing techniques for rapid prototyping of acoustic materials and metamaterials.