Effect Of Geometry Of Front And Rear Disks On The Aerodynamic Performance And Internal Flow Characteristics Of A Volute-free Centrifugal Fan

Backward volute-free centrifugal fans play an important role in the industrial field because of their advantages of small size,high efficiency and low noise.The front and rear disks of the impeller are the main connecting structures of the impeller of the centrifugal fan.The transformation of the structure will change the flow path of the impeller and have a significant influence on the aerodynamic performance and noise characteristics of the fan.In this paper,the backward volute free centrifugal fan is taken as the research object,and the aerodynamic performance,internal flow characteristics and noise characteristics of the fan under different shapes of front and rear discs are studied by combining numerical simulation with experimental testing.In order to arrange the fan in the case of limited space,the driving motor is often partially installed in the impeller domain,and the shape of the fan rear disk changes with the size and geometry of the invading motor.In this paper,the aerodynamic performance,flow characteristics and noise characteristics of the fan are analyzed by directly changing the height of the intrusion motor.Firstly,the numerical simulation and experimental test of fan models with different invasion motor heights are carried out.The research shows that the increase of invasion motor height can reduce the static pressure and static pressure efficiency of the fan in different degrees under three flow conditions.At large flow rate,the height of the motor decreases the static pressure and static pressure efficiency of the fan more obviously.At a small flow rate,the separation vortex in the blade passage blocks the gas flow and reduces the static pressure rise.The increase of motor height has little influence on the flow inside the fan.Under the design flow rate,a separation vortex is formed at the suction front edge.When the motor height exceeds a certain value,the flow in each blade passage is uneven.With the increase of motor height under large flow,the pressure distribution of fan front disk and rear disk is uneven.The blockage caused by the intrusion motor is more obvious and the fan performance deteriorates significantly.The instability of the flow in the fan increases with the increase of the height of the motor in the form of increased velocity and pressure fluctuations.Since the flow changes from axial to radial at the inlet of the fan,a pair of counter-rotating vortices are formed at the motor and rear disc,increasing the flow loss.When the height of the motor increases to a certain value,the noise of the fan deteriorates obviously.In order to analyze the influence of different front disk shapes on fan performance,this paper adjusts the governing equation of different front disk edge radian profile based on Matlab to obtain impeller with unequal outlet height.The results show that the flow area of impeller passage is increased and the working range of impeller is expanded by adjusting the cambel of front panel edge.Under the condition of large flow rate,the static pressure and static pressure efficiency of fan are increased obviously.Overall,the flow condition of the impeller near the front disk is improved,the radial velocity fluctuation of the impeller outlet is weakened,the secondary flow and the return area are reduced,and the jet wake structure of the main stream in the middle disk is weakened.Compared with the uniform arrangement of the edge line of the impeller front plate,the pressure pulsation of the impeller pressure surface with eccentric arrangement and near the outlet of the front plate is larger.Under the design flow condition,the noise at the inlet of the fan is worsened by adjusting the camber of the front panel edge,and the sound pressure level at the outlet is less affected.