Flow-Acoustics: Theory and Benchmarking
Stefan Schoder
TL;DR
This work tackles aeroacoustic fan noise in green heating systems under TA-Lärm-type regulations and presents FAN-01 as an experimental benchmark for axial fans in a short duct. It evaluates a hierarchical set of prediction methods—from empirical VDI 2081 and VDI 3731 to Sharland and Költzsch spectral models, through hybrid PCWE/FWH approaches, to fully compressible DNS using LBM/VLES—against FAN-01 measurements, including $L_W$ around $87.3~\mathrm{dB}$ and spectral content. Results show simple empirical predictions yield $L_W$ in the mid-80s to high-80s dB range, while hybrid and DNS predictions reproduce both broadband and tonal content more accurately (e.g., PCWE $L_W=86.7~\mathrm{dB}$, FWH $L_W=85.2~\mathrm{dB}$, DNS $L_W=86.7~\mathrm{dB}$), closely matching the measured $L_W$. The study demonstrates that class-3 and class-4 methods are viable for optimization of axial-fan noise in practical, regulation-driven design, while highlighting substantial computational costs for high-fidelity simulations and suggesting future exploration of transient operating-point effects and ML-assisted optimization.
Abstract
The urgent need for transitioning to green energy solutions, particularly in the context of house heating and urban redensification, has brought the issue of fan noise aeroacoustics investigations to the forefront. As societies worldwide strive to mitigate climate change and reduce carbon emissions, adopting sustainable heating technologies such as air heat pumps has gained significant traction. In Germany, renowned for its commitment to environmental sustainability, the "TA Lärm" regulations, derived from the "Bundes-Immissionsschutzgesetz," impose stringent limits on noise levels both inside and outside buildings across various applications. These regulations delineate permissible noise levels during daytime (6 AM to 10 PM) and nighttime (10 PM to 6 AM), with particular emphasis on protecting residential areas with low noise limits. Moreover, the noise limits prescribed for indoor environments are even more stringent. Given the necessity of maintaining acoustic comfort and quality of life, compliance with these regulations necessitates meticulous attention to noise generation sources, especially those associated with heating and ventilation systems. Consequently, understanding and mitigating fan noise through aeroacoustic investigations is essential to ensure the successful adoption and integration of green energy solutions in residential and urban settings. In the following, an experimental benchmark for a low-pressure rise axial fan (FAN-01) is presented, and several prediction methods of the sound pressure and sound power are evaluated.