GRAS Innovation Award 2025 – Industrial Application Winner

In a joint effort between ECUST and Tongji University, researchers have advanced the science of flow-duct noise control through the development of a new type of side-branched Helmholtz resonator with embedded apertures (HREA). The innovation targets aerodynamic noise problems common in HVAC, refrigeration, and aerospace ducting, where conventional silencers lose efficiency under grazing flow.

To validate their theoretical and numerical models, the team conducted a detailed experimental campaign using four GRAS 46AE ¼″ Free-Field Microphones mounted along the duct wall in a semi-anechoic room. Each sensor, with a frequency range of 3.15 Hz to 20 kHz and a sensitivity of –26 dB re 1 V/Pa @ 250 Hz, was calibrated with a GRAS pistonphone before testing.

The microphones captured the transmission-loss characteristics of various resonator configurations under air-flow velocities up to 34.3 m/s, allowing comparison with COMSOL Multiphysics simulations and theoretical predictions. Results showed up to 40 dB attenuation at 66 Hz and sustained broadband damping even in strong flow conditions.

These findings open the door to new generations of compact, thin, and tunable acoustic mufflers. GRAS microphones provided the accuracy and stability needed to quantify minute acoustic variations in turbulent flow—confirming their essential role in advanced industrial-acoustics research worldwide.