Study On Matching Between Impeller And Volute Of Centrifugal Fan With High Specific Speed

Centrifugal fans are widely used in various fields of industrial production,and are also the main energy consumption equipment.With the progress of the society and the improvement of the level of science and technology,in the practical application,the demand for the flow of the fan increases,which makes the fan deviate from the design working condition during operation and greatly reduce the efficiency.Therefore,in most of the fan energy conservation projects,the original fan impeller is usually replaced with a impeller of high specific speed.Although the newly developed high-specific speed impeller greatlly improves the operation efficiency of the traditional centrifugal fan,there is still a relatively high flow loss in the fan due to the poor matching between the impeller and the volute.At the same time,a large axial force will be generated when the high-specific speed impeller rotates.which affects the operation stability of the fan and incrreases the bearing loss.Therefore,The key to optimize the design is to study the flow mechansim inside the high specific speed centrifugal fan.On the basis of replacing the impeller of high specific speed in the 4-73 centrifugal fan,the three-dimensional unsteady mumerical calculation model is cstablished and tested.By means of high speeed centrifugal fan of unsteady flow field and pressure pulsation signal analysis reveals that the ventilator internal flow loss mechanism,and USES the different width volute,impeller and volute of different rclalive position,adding guide plate inside the volute impeller and add die back side of the open balance hole reinforcement method of high speed centrifugal fan is optimized.The main research contents and conclusions are as follows:(1)Internal flow loss mechanism of centrifugal fan with high specific speed,Through the analysis of flow field and pressure pulsation signal in different flow condition of centrifugal fan with high specific speed,the loss mainly exists in the impeller and volute,among which the loss mainly exists in the front plate of the impeller.The loss of volute is nearly 12.4%,which is mainly distributed near the anti-vortex ring and volute tongue.The gas forms two interacting vortex belts in the volute and has strong unsteadiness.(2)Improve the matching degree of the impeller and the original volute.In order to reduce the loss of the volute and enhance the matching degree of the impeller and the volute,the influences of the original width of the volute and the central position of the impeller on the centrifugal fan with high specific speed were studied without changing the impeller with high specific speed.The results show that after optimizing the width of the volute,the efficiency of the fan can be improved by 0.95%at full pressure and at constant design speed.After optimizing the central position of the impeller,the total pressure of the fan is basically unchanged,the efficiency is increased by 2.21%,the specific speed is increased by 10.6%,and the matching between the impeller and the volute is improved in the condition of large flow.The improvement of fan efficiency is mainly due to the reduction of flow loss in the volute.When the relative position of the impeller and the volute is changed,the strength of the secondary vortices in the volute is reduced,and the interaction strength between the secondary vortices and the primary vortices is also reduced.The distribution of turbulent kinetic energy and the amplitude of low-frequency pressure pulsation in the primary and secondary vortices are significantly reduced.Therefore,by optimizing the width of the volute and the central position of the impeller,the matching between the impeller and the volute can be improved,and the working efficiency of the fan under the condition of large flow can be further improved.(3)In order to reduce the axial force of the impeller and enhance the matching degree between the impeller and the volute,the influence of balance holes and reinforcing bars on the performance of the centrifugal fan was studied without changing the original volute.The research shows that the fan efficiency increases by 1.78%and the axial force decreases by 1.9%after opening the balance hole.The improvement of fan eff-iciency is mainly due to the reduction of flow loss in the volute by 1.68%.(4)In the process of optimizing the matching design of the impeller and the volute at high specific speed,the volute in the fan suffered serious losses.Under the optimal parameters,the efficiency of the fan at the design working point increased by 1.57%and the loss of the volute decreased by 1.53%.