Effect Of Inclined Volute On The Aero-acoustic Performance Of Multi-blade Centrifugal Fan

The inner flow of multi-blade centrifugal fan is very complicated and the airflow distribution in the axial direction is uneven because the diameter ratio and relative width of impeller are larger. Considering the non-uniform internal-flow of multi-blade centrifugal fan and the feature of internal-flow is closely connected with the noise, the effect of inclined volute on the flow condition and the aero-acoustic performance of multi-blade centrifugal fan are studied, based on the rectangular volute fan. It aims to find new ways to improve the aerodynamic performance of multi-blade centrifugal fan and reduce the fan noise.Influence of axial inclined volute on the performance of multip-blade centrifugal fan is studied. The performance curve of fan and the flux through the passage of the impeller along the axial direction are obtained. The results show that with the increase of the inclination degree, the total pressure of the fan is increased first and then decreased, which is more obvious under the condition of large flow rate. The flux through the passage at the middle and rear side of the impeller increases due to the axial inclined volute. The velocity of the inner part of volute improves and the velocity distribution of air flow is more uniform. Moreover, the separation vortex in some flow channels is reduced and the vortex flow in the inclined volute is weakened. The vortex near volute side plate reduces and thins.Effect of circumferential inclined volute on the performance of multip-blade centrifugal fan is researched. The performance curve of fan and the total pressure through the passage of the impeller along the circumferential direction are concluded. The results show that with the increase of the inclination degree, the total pressure of the fan is increased and the growth rate gradually decreased, which is more obvious under the condition of large flow rate. Due to the circumferential inclined volute, the total pressure of impeller outlet is enhanced and the stagnation point near the volute tongue is changed.The total pressure of part areas of volute outlet improves and the total pressure distribution is more uniform. Moreover, the vorticity of impeller flow channel and inner part of volutereduces and the flow separation phenomenon in flow channel decreases, lead to decrease in the area of flow separation.Influence of inclined volute on the acoustic performance of multi-blade centrifugal fan is studied, applied with the large eddy simulation and acoustic boundary element method. The results show that the larger acoustic pressure value of far field mainly distributes in the area near the outlet of volute and its opposite side. The acoustic pressure in the area before and after the rotating shaft is smaller. The pressure fluctuation on the impeller is weakened and the acoustic pressure of the near and far field is reduced,because of the appropriate axial inclined volute or circumferential inclined volute. Caused by the air flow from impeller to volute, phase difference has a greater impact on reducing the noise of the near and far field of the centrifugal fan than the big gap between impeller and volute.