Study On The Effects Of The Shape Of Volute Tongue On Unsteady Flow Characteristics Of A Centrifugal Fan

The forward multi-blade centrifugal ventilator is widely used,and its internal airflow has complex motion characteristics under the interaction between the impeller and the volute.As the most important part of the volute wall structure,the shape of the volute tongue will have a significant impact on the aerodynamic and noise characteristics of the fan.Based on the experimental verification of the accuracy of the numerical simulation,by changing the shape of the volute tongue,we conducted numerical simulations using both steady Reynolds-Averaged Navier-Stokes(RANS)and unsteady Reynolds-Averaged Navier-Stokes(URANS)approaches.The general characteristics of airflow in the volute are analyzed globally,and the flow characteristics on the volute wall,the backflow conditions inside and outside the impeller,the flow characteristics of the surface of volute outlet,the pressure pulsation in the volute and its propagation characteristics are studied locally,and the noise characteristics of the fan are also obtained by experiments.In order to analyze the influence of directly changing the radius of the volute tongue on the fan,a group of fan models with different radius of the tongue were numerically simulated and experimentally tested.It is found that the decrease of the radius of the volute tongue can increase the static pressure of the fan,meanwhile,the amplitude of the pressure pulsation will increase significantly,and the strong pressure pulsation exists in almost every position.When the radius of the volute tongue is small,there will be some better flow characteristics,for example,there is a lower pressure and a smaller high-pressure concentration area at the volute tongue,the backflow in the impeller passages is reduced,the forward flow velocity is increased,and the static pressure value of some points inside the volute is lower,etc.It should be pointed out that some excellent internal flow characteristics is not stable,it is in a state of change,such as the low pressure range at the impeller passages is only generated at T2,and does not exist at other times,the radial velocity in the impeller passages is higher in some areas and less backflow,but the forward velocity is smaller in other areas,and so on.In addition,some unfavorable flow characteristics have also appeared,such as the flow at the wall of the volute is more prone to instability and the pressure pulsation is larger.And the high noise result measured by the experiment may be related to the larger pressure pulsation amplitudeIn order to analyze the influence of directly changing the radius of the volute tongue on the fan,a group of fan models with different radius of the tongue were numerically simulated and experimentally tested.It is found that the decrease of the radius of the volute tongue can increase the static pressure of the fan,meanwhile,the amplitude of the pressure pulsation will increase significantly,and the strong pressure pulsation exists in almost every position.When the radius of the volute tongue is small,there will be some better flow characteristics,for example,there is a lower pressure and a smaller high-pressure concentration area at the volute tongue,the backflow in the impeller passages is reduced,the forward flow velocity is increased,and the static pressure value of some points inside the volute is lower,etc.It should be pointed out that some excellent internal flow characteristics is not stable,it is in a state of change,such as the low pressure range at the impeller passages is only generated at T2,and does not exist at other times,the radial velocity in the impeller passages is higher in some areas and less backflow,but the forward velocity is smaller in other areas,and so on.In addition,some unfavorable flow characteristics have also appeared,such as the flow at the wall of the volute is more prone to instability and the pressure pulsation is larger.And the high noise result measured by the experiment may be related to the larger pressure pulsation amplitudeIn order to avoid the influence of factors such as the increase of the volute tongue gap and the decrease of the volute wall length at the exit caused by directly changing the radius of the volute tongue.In this paper,a set of the shape of volute tongue is obtained based on the Bezier curve method,and its variable is mainly the distance between the smaller area of the volute tongue and the trailing edge of the impeller.The results show that the proper distance will not affect the aerodynamic performance of the fan,and will produce some beneficial effects such as reduced backflow at the inlet and outlet of the impeller passages,more stable wall flow,and lower air impact intensity near the volute tongue.However,some flow characteristics are still unfavorable,such as significant unsteady characteristics of static pressure,large pulsation amplitude,etc.And when deviating from this distance,the aerodynamic performance of the fan will be significantly reduced.The comparison of the results of RANS and URANS approaches shows that the RANS approach can indicate the aerodynamic performance of the fan and the flow characteristics of each area to a certain extent,but the numerical accuracy and the resulting turbulence intensity,velocity change characteristics and pressure propagation characteristics and other information are relatively low in accuracy.