A novel honeycomb core design combining elliptical annular structures with re-entrant hexagonal structures was proposed, and a new auxetic honeycomb sandwich panel coated with polyurea was developed to enhance its vibroacoustic performance. A numerical model of the novel auxetic honeycomb sandwich panel was established using ABAQUS software and validated. The vibration and acoustic responses of four different configurations of the novel auxetic honeycomb sandwich panel were analyzed through numerical simulations. The results indicate that the polyurea coating location and honeycomb geometry enable the sandwich panel to effectively reduce vibration and suppress noise. The symmetric structure (P-4 panel) of the honeycomb sandwich configuration outperforms the asymmetric structures in both vibration reduction and sound insulation. The sandwich panel with a 6 mm polyurea coating exhibits the lowest peak and fastest decay in sound pressure level (SPL), along with a 7.6% improvement in average sound transmission loss (STL). The honeycomb geometries α = 1 and μ = 1 demonstrate the most superior vibroacoustic characteristics in the sandwich panel.
This study numerically investigates the effect of low-momentum blowing applied to a toroidal propeller on aerodynamic performance and aeroacoustic characteristics. A Delayed Detached Eddy Simulation (DDES) approach coupled with the Ffowcs-Williams and Hawkings (FW-H) acoustic analogy is employed to resolve unsteady flow structures and predict far-field noise signatures. Two configurations are examined at 3000 revolutions per minute (RPM): a baseline propeller and one equipped with active flow control (AFC). The results show that the introduction of AFC produces negligible changes in thrust, torque, and figure of merit (FM), indicating that equivalent aerodynamic performance is maintained. In contrast, noticeable acoustic benefits are achieved. Significant reductions in primary tonal noise and overall sound pressure level (OASPL) are observed along the propeller axis direction, with a maximum tonal reduction of approximately 6 dB and an OASPL decrease of up to 1.8 dB. Flow-field analysis using Q-criterion iso-surfaces and z-vorticity contours reveals that blowing weakens coherent vortex structures near the upper surface of the back blades around 0.75. The weakened vortical activity reduces unsteady surface pressure fluctuations, thereby attenuating dipole-type acoustic sources responsible for dominant axial radiation.
In this study, a numerical investigation is conducted to examine propeller performance, flow physics, and aeroacoustic signatures of a toroidal propeller in ground effect (IGE). Delayed Detached Eddy Simulation (DDES) is employed to resolve propeller performance, flow structures, vortex formation, and surface pressure fluctuations across a range of normalized ground spacings. Aeroacoustic predictions are obtained using Ffowcs Williams-Hawkings (FW-H) acoustic analogy to quantify primary tonal noise, broadband noise, and overall sound pressure level (OASPL). The numerical results reveal that descreasing ground spacing leads to more thrust augmentation compared to two conventional propellers. Thrust, torque, and figure of merit (FM) all exhibit asymptotic trends with respect to ground spacing. Compared with experimental results, the numerical simulations predict propeller thrust more accurately than torque. Flowfield analysis indicates that this performance enhancement is primarily driven by ground-induced flow recirculation and a localized upflow underneath the propeller, rather than by the classical fountain-effect mechanism. Vorticity analysis further reveals increased coherence and confinement of the tip vortices at small ground spacings. From an aeroacoustic perspective, ground effect produces a pronounced modification to noise directivity. The primary tonal noise exhibits a quadrupole-like directivity pattern that weakens and nearly vanishes along the rotation axis at small ground spacings, consistent with enhanced destructive interference of coherent loading sources. In contrast, broadband noise and OASPL display predominantly dipole-like directivity and increase toward the rotation axis, driven by increased turbulence and unsteady flow interactions associated with the upflow.
This paper investigates the acoustic radiation from a semi-infinite cylindrical duct with multiple axial impedance discontinuities on the inner surface and a uniformly coated outer surface. The inner surface is divided into three consecutive impedance-lined segments, each characterized by a distinct impedance value, forming a coupled multi-region configuration. The problem is analyzed using the Wiener-Hopf technique for two geometrical configurations, namely a duct with an infinitely thin wall and a duct with finite wall thickness. For each case, the governing Helmholtz equation is reduced to a Wiener-Hopf equation via Fourier transform, and the unknown modal coefficients are determined through Dini series expansions and enforcement of the boundary and continuity conditions at each interior junction. The far-field directivity pattern is obtained via the saddle-point method. Numerical results illustrate the effects of the duct radius, frequency, segment lengths, and impedance parameters on the radiated field. The finite wall thickness formulation is shown to recover the thin wall solution in the limit , and the results are validated against existing solutions in the literature.
This research presents the design, numerical optimization, and experimental validation of two bio-inspired membrane-type acoustic metamaterials-one based on a hexagonal honeycomb topology and the other on a spider-web configuration-for targeted low-frequency sound insulation in railway cabins. Field noise measurements from Fadak passenger trains identified two dominant interior frequency bands: a primary peak near 630 Hz and a secondary band around 1.6 kHz. The proposed meta-panels were modeled as full three-dimensional cellular arrays in COMSOL Multiphysics, with sound transmission loss (STL) computed in 1/6-octave bands and analyzed through modal decomposition. The honeycomb design, characterized by a lower first natural frequency, demonstrated enhanced attenuation at very low frequencies, whereas the spider-web structure exhibited a denser modal distribution, enabling broader suppression near 1.6 kHz. A constant volume/mass parametric analysis was followed by a single-objective Nelder-Mead optimization to maximize STL at 630 Hz by tuning two key geometric parameters. The optimized configurations achieved up to similar to 10 dB improvement at the target frequency, with the honeycomb variant offering superior performance-to-mass ratio, and the spider-web variant delivering stronger attenuation peaks at the expense of increased mass. Prototypes fabricated via fused deposition modeling (FDM) using flexible thermoplastic polyurethane (TPU) and thin polyethylene membranes were tested in a coupled reverberant-anechoic setup, confirming the numerical predictions. These findings demonstrate that the integration of bio-inspired geometries with lightweight, flexible membrane structures enables precise control of low-frequency acoustic performance. The proposed designs offer a scalable and weight-efficient solution for mitigating interior noise in railway passenger environments, with potential applicability across a range of transportation and architectural contexts.
