Numerical investigation of tonal noise sources from centrifugal fan
Licentiate thesis, 2020

Heating, ventilating, and air conditioning systems (HVAC) are today an important part of many people's life. They provide a sufficient amount of airflow with the correct temperature, quality, and humidity. The negative side is the noise it produces. Many improvements have been made in building development to reduce noise from the environment. When so, the noise from the HVAC system becomes clearer. The dominant tonal noise in an HVAC system is produced by the fan. In this work tonal noises produced by a centrifugal fan is investigated to be able to understand the generation mechanism and identify their sources. The approach is to use the hybrid computational aeroacousticsĀ  (CAA) method, that couples a computational fluid dynamics (CFD) method with the Ffowcs Williams and Hawkings (FW-H) acoustic analogy.

Recirculating flows, which are responsible for reducing the fan efficiency and increasing the noise generation, are observed between the shroud and the blade trailing edges. It is found that the recirculating flows are associated with the gap between the shroud and the inlet duct.

The recirculating flow causes large modeled turbulence kinetic energy (TKE). The TKE is unevenly distributed among the blades due to the unsteady recirculating flow. Moreover, the position of the largest TKE periodically varies among the blades. The period corresponds to approximately 4 times the fan rotation period, it was also found in acoustic measurements.

Different pressure distributions among the blades are found and ascribed to the turbulence initializing from the inlet gap. The turbulence develops along the shroud wall and interacts with the blades at their leading edges. The interaction renders uneven surface pressure distributions among the blades as well as significant peak differences. As the distances to the inlet gap and the shroud increases, the difference of the pressure distributions among the blades decays. The wall-pressure fluctuations indicates that the locations of the tonal noise sources agree with the locations of the uneven surface pressure distributions and the significant pressure peaks, which are near the blade leading edges.

Centrifugal Fan

Blade Passing Frequency

Computational Aeroacoustics

Tonal Noise

Opponent: Prof. Mats Åbom, Department of Aeronautical and Vehicle Engineering, KTH Royal Institute of Technology, Sweden


Martin Ottersten

Chalmers, Mechanics and Maritime Sciences, Fluid Dynamics

Martin Ottersten, Hau-Dong Yao and Lars Davidson - Numerical and experimental study of tonal noise sources at the outlet of an isolated centrifugal fan

Subject Categories

Mechanical Engineering

Aerospace Engineering

Energy Engineering

Fluid Mechanics and Acoustics

Driving Forces

Sustainable development

Areas of Advance



Chalmers Maritime Simulators


Chalmers University of Technology


Opponent: Prof. Mats Åbom, Department of Aeronautical and Vehicle Engineering, KTH Royal Institute of Technology, Sweden

More information

Latest update