Abstract: and thereby reduce pipeline vibration and noise. Three-dimensional gas-liquid two-phase flow models with various pipe geometries were implemented in OpenFOAM, considering CO₂ dissolution in water, and solved using the reactingTwoPhaseEulerFoam solver. Based on the sound-speed characteristics of each medium, four Helmholtz-type resonators with distinct resonance frequencies (Resonators 1-4) were designed, and their attenuation performance under M-sequence excitation of inlet pressure and flow rate was evaluated. The simulation results reveal that, in the inverted configuration, Resonator 1 achieves approximately 40% attenuation near 422 Hz, and Resonator 3 delivers 65% and 62% attenuation at 872 Hz and 725 Hz, respectively. In the upright configuration, Resonator 4 suppresses the 813 Hz peak by over 70%, whereas Resonator 2 yields about 12 dB attenuation only around 1383 Hz. To validate these findings, a test platform equipped with pressure and sound-level sensors was constructed, and the experimental results were compared with the numerical results. Experimental trends closely matched simulations: under gas-filled conditions, Resonator 4 reduced pressure pulsation peaks by 68% and sound pressure level by 5 dB; under liquid-filled conditions, Resonator 3 achieved 64% and 6 dB attenuation; when identical resonators were arranged in series upright, both attenuation and noise reduction were further improved by about 10%. The variation in attenuator performance is primarily attributed to the alignment between the cavity’s natural frequency and the characteristic frequencies of the two-phase flow. When the cavity is dominated by gas, the effective sound speed is relatively low, which facilitates the attenuation of low-frequency pulsations in the flow. In contrast, when the cavity is largely filled with liquid, the higher effective sound speed enhances the damping of higher-frequency pulsations. Moreover, the installation configuration can modify the gas-liquid distribution, thereby influencing both the effective sound speed and modal properties, constituting a key factor in the observed differences in attenuation performance.