| The internal flow of a multi-blade centrifugal fan is unsteady.The characteristics of separation and secondary flow in different positions is important factors affecting the noise and performance of a multi-blade centrifugal fan.Many scholars improve performance and noise by techniques of flow control.The paper researchs targeted high-precision numerical calculation and corresponding internal and external characteristic tests to explore a numerical method that can truly reflect the internal complex flow of the the multi-blade centrifugal fan.According to the mature flow control methods at home and abroad,an effective control method for the multi-blade centrifugal fan was proposed to improve performance and reduce noise.(1)The paper refers PIV test and bases on the applicability of Spalart-Allmaras,Realizable ?-? and SST ?-? in numerical computation of multi-blade centrifugal fans.The results show that SST ?-? is more suitable for fan calculation.According to performance test,the internal and external characteristics of fan calculations was compared between polyhedron,hexahedral,hexahedral and tetrahedral grids.The results show that the polyhedral grid is more suitable for fan calculation.(2)While keeping the same impeller diameter,match of impeller and volute was studied for the volute outlet with or without restrictions.First,the influence of the volute opening degree on the aerodynamic performance is determined.Finally,the reasonable range of the parameters for controlling the the volute opening degree is obtained.(3)The fan with unlimited and limited inlet is proposed to provide a method of collector eccentric installation to control and improve flow of inlet.With unlimited on inlet,results of research shows that when the eccentric angle is set to 120° and the offset ratio set to 0.016,the fan volume rate increase by 3.5%,the total efficiency increase by 3% and Aweighted SPL decreases by 1.2dB.The flow separation in the blade passages of the eccentric direction is weakened,and volume rate of impeller outlet increases,meanwhile the gap flow leakage between front disc and the nozzle decrease.The intensity of the noise source of fan at the fundamental frequency and twice the frequency is reduced,the distribution of fan noise around fan is improved,and the noise is reduced.With limited on inlet,results of research shows that when the eccentric angle is set to 240° and the offset ratio set to 0.016,the fan volume rate increase by 9%,the total efficiency increase by 8% and A-weighted SPL increases by 1.2 dB.The unsteady vortex at the inlet of the fan moves towards the center of the impeller,and the flow separation in the blade passages decreases.The intensity of the noise source of fan at the fundamental frequency and twice the frequency is reduced,the distribution of fan noise around fan is improved,and the noise is increased slightly. |
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