Vortex Loss Mechanis And Optimization Design Of Volute For Centrifugal Ventilator G4-73

Centrifugal ventilator,as a main equipment for gas transmission,has the advantages of large air volume and low cost,and is widely used in various fields such as industry,chemical industry,forestry,irrigation and environmental protection,and is also one of the main energy-consuming equipment.Therefore,to further improve its operation efficiency is one of the important development directions of China’s energy saving,emission reduction and sustainable development strategy.The vortex loss inside the volute accounts for a large proportion of the whole centrifugal ventilator loss.It is an important direction to improve the efficiency of the centrifugal ventilator to reduce the vortex loss by improving the vortex structure in the volute.Based on the G4-73 centrifugal ventilator test platform built in the laboratory,this paper adopts the method of combining experiment and numerical simulation to design and optimize the diffused volute based on in-depth analysis of the vortex loss mechanism in the volute,which reduces the vortex loss in the volute and improves the efficiency of the ventilator.The main research contents and achievements of this paper are as follows:(1)The external characteristics and pressure pulsation experiments of the centrifugal ventilator were carried out,and combined with the unsteady numerical simulation results of the whole channel,it was found that the volute loss accounted for 65%of the total loss of the centrifugal ventilator,and was the main source of the loss inside the centrifugal ventilator.According to the mechanism analysis,due to the disturbance of airflow at the impeller outlet and the presence of the volute tongue,three vortexes with high turbulent kinetic energy formed in the flow channel near the volute tongue.The vortex intensity and turbulent kinetic energy gradually and the presence of the volute tongue,three vortexes with high turbulent kinetic energy formed in the flow channel near the volute tongue.The vortex intensity and turbulent kinetic energy gradually decreased along the main flow of the volute,but suddenly increased at the position near the outlet of the volute tongue.The interaction of three vortices with high turbulent kinetic energy leads to a large flow loss in the volute,and with the decrease of flow,the large-scale vortices break,and the high turbulent kinetic energy vortices in the volute gradually move to the front disk of the impeller.(2)The diffusion volute is designed according to the vortex loss mechanism in the volute.The DOE experimental design method is used to carry out parametric research on the two variables of the front and back diffusion angles of the volute.It is found that with the increase of the front diffusion angle,the fan efficiency increases first and then decreases,and reaches the maximum at 25°.When the fan efficiency is greater than 25°,the fan efficiency decreases,and the rear diffusion angle has relatively little effect on the fan efficiency.Through the parametric study,the optimal diffusion angle is 25°,and the efficiency of the design point of the fan is increased by 2.24%.(3)Mechanism of diffusion-type volute on vortex structure improvement and loss reduction:The diffusion-type volute destroys the large-scale vortex in the prototype volute and becomes a small-scale vortex with low turbulent kinetic energy,the high vortex intensity area in the volute is reduced,and the non-constability of the vortex in the prototype volute is weakened,and the flow field inside the volute is significantly improved,thus reducing the loss of the volute.The diffused volute also effectively reduces the amplitude of pressure pulsation in the volute,especially for shaft frequency and 0.22fn signal,which reduces the amplitude of low-frequency disturbance caused by unstable flow caused by vortices.Under the design condition,the diffused volute reduces the volute loss by 30.8%,and the overall fan efficiency is increased by 2.24%.