Study On The New Blade Shape Performance And Noise Characteristics Of Counter-rotating Fan

The counter-rotating fan has the advantages of compact structure,large flow range,high pressure rise and high efficiency,convenient air reversing,and is widely used in many industrial fields.The shape of the moving blade has a great influence on its performance,especially when reversed ventilation,the unfair design of the blade shape will greatly reduce its performance.In this paper,the C-4 airfoil is used as the original airfoil.The double-headed positive-symmetrical tip blade and double-headed positive-symmetrical blunt blade counter-rotating fan are designed.The original airfoil and two new blade are designed by numerical simulation.The performance and noise characteristics of the counter-rotating fan were studied.Through the steady simulation calculation,it was found that under normal ventilation(forward)operation,under the condition of design flow(44000m3/h),the pressure and power of the double-headed tip blade are respectively higher by 17.11%and 16.35%than the original airfoil.The pressure and power of the double-headed blunt blade are respectively lower 6.3%and 6.02%than the original airfoi.The internal efficiency of the tipped blade and the blunted blade was 2.02%and 1.12%higher than that of the original airfoil.In the case of air reversing(with 85%of design flow),the pressures of the tipped blade and the blunted blade are 25.1%and 36.6%higher than those of the original airfoil,and the power is 27.5%and 31.2%higher than the original airfoil respectively.The efficiency is 4.9%and 18%higher than the original airfoil.It is thus concluded that the performance of the counter-rotating fans with two kinds of modified blade is better than that of a counter-rotating fan with a original airfoil,regardless of whether it is forward and reverse running.From the time domain chart of the pressure fluctuation at the monitoring point located near the fan blade,it was found that at the inlet of the first stage,the tip of the tipped blade had minimal airflow disturbance,while the blunted blade had the greatest airflow disturbance.When the stage blade inlet flows to the two-stage blade interference,the three blade pressure fluctuation range become smaller all,but the fluctuation range of the original airfoil and the tipped blade are greater than the blunted blade.At the second stage blade outlet,two kinds of modified blade disturbances are larger than the original airfoil.Comparing the pressure fluctuation spectrum charts inthe tip of the three kinds blade,it was found that the occurrence frequency of blade pressure fluctuation peaks was basically the same as that of the two stage.In the blade head,two stage have the highest pressure fluctuation in the original airfoil,followed by the tipped blade and the blunted blade.In the middle,the pressure fluctuation still exists with increasing frequency,which shows that this is the main part of the airflow vibration.In the tail of the blade,the blunted blade has the greatest airflow disturbance due to the shape of the trailing edge.Analyze the vortex intensity at the first-stage inlet,two-stage interference,and the second-stage outlet:At the inlet of the first stage,the impact of airflow on the original airfoil is mainly except for the blade root.In the middle of the blade,the impact on the double tipped blade tip is the smallest,and the impact on the double tipped blade blade root is greater.At the two-stage impeller interference surface,the double tipped blade tail has not yet undergone a clear deformation,while the double-headed obtuse blade The deformation of the shape of the wake is the most serious;at the exit of the second stage,the high vorticity area of the original airfoil is mainly concentrated in the hub and the casing,while the two modified leaf shapes still have high vorticity areas in the flow channel.By predicting the far-field noise of the three leaf-shaped counter-rotating fans,it was found that the noise of the double tipped tip leaves was the largest,followed by the original airfoil and the double-headed obtuse leaf-shaped,and the maximum sound pressure value was located at the passing frequency of the impeller.nearby.According to the noise-directivity distribution diagram,it can be seen that the counter-rotating fan has dipole characteristics in the external acoustic field radiation.