Relationship between volute pressure fluctuation pattern and tonal noise generation in a squirrel-cage fan

In this work, the pressure fluctuation pattern in the volute of a squirrel-cage fan is analyzed. Also studied is how this pattern is modified when a slight geometry change is introduced in the volute tongue. The study has been carried out on a commercial machine, used in automotive air conditioning units. A three-dimensional and unsteady numerical simulation of the flow in the complete machine has been carried out using the commercial code FLUENT. In this way, the pressure fluctuations in some locations near the volute wall have been obtained. The results of this numerical simulation have been compared to the sound pressure level spectra radiated by the fan, measured in a ducted test installation at the laboratory. The tendencies of the sound pressure levels measured at the blade passing frequency show a good correlation with the amplitudes of pressure fluctuations obtained numerically near the volute wall.