Flow stabilization and velocity uniformity in a Göttingen-type closed-circuit subsonic aerodynamic wind tunnel with an expanded test section are investigated in this study. Both experimental and numerical approaches were employed. The experiments were performed by using Laser Doppler Anemometry, Pitot tubes, and thermal anemometry. For numerical simulations, Reynolds-averaged Navier–Stokes simulations with a standard k-ε turbulence model were employed to evaluate flow characteristics in the velocity range of 0.05–20 m/s. The study shows that a properly contoured contraction nozzle suppresses inlet turbulence and ensures stable Reynolds-independent core flow. The contraction nozzle significantly accelerates and redistributes the flow, allowing rapid hydrodynamic stabilization and ensuring velocity measurements with high repeatability. These characteristics are inherent in a benchmark facility. Additionally, the study shows that the outlet-to-inlet diameter has the most prominent role in longitudinal velocity distribution in the test section. An optimal ratio of 1.10 was identified, stabilizing the pressure distribution and providing the most uniform longitudinal velocity profile. These findings offer geometry-dependent design guidelines for achieving high-quality measurements in Göttingen-type wind tunnels with expanded test sections and support accurate velocity measurement instrument calibration and aerodynamic testing.

Acoustic agglomeration is a potential pretreatment for reducing fine particulate matter (PM) emissions from industrial flue gas. This experimental study examined biomass-derived fly ash particles exposed to standing high-intensity sound waves, addressing an aerosol type that has received less attention than coal-derived fly ash. The effects of acoustic frequency (16–36 kHz), sound pressure level (SPL; 110–135 dB), chamber residence time (τr; 2–8 s), and initial particle number concentration (2 × 104–13 × 104 cm−3) were investigated. Under the specified laboratory conditions, PM2.5 number concentration decreased by 72.5% and 87.6% at 16 and 32 kHz, respectively, at an SPL of 135 dB, τr= 4 s, and an initial PM mass concentration of 175 mg m−3. Agglomeration efficiency increased with τr and SPL across the tested ranges, tending toward saturation at the highest exposures.