| For the mining contra-rotating primary fan with push-in operation,the uniformity and stability of the intake air have a very important influence on the safety of the impeller blade work.When the unstable airflow generated in the 90°bend of the intake duct flows through the impeller,it can easily cause blade fatigue failure,cracks,and even broken accidents,which poses a serious threat to the safety production of the coal mine.In this paper,the FBCDZ-10-No36 mining contra-rotating primary fan is chosen as the study object.We investigate the installing of guide vanes in the 900 bend of the intake duct and the optimization of the arrangement of guide vanes,aiming to improve the uniformity and stability of air flow in the air inlet of the air duct and the impeller,and then improve the safety of the fan,which has great theoretical significance and engineering application value.The main research work and conclusions are as follows:The geometry of the intake duct in front of the first-stage impeller is modeled,and the large-eddy simulation(LES)method is used to numerically simulate and comparative analyze the flow field before and after the installation of guide vanes in the intake duct.The results show that,before the installation of the guide vanes,the mainstream flow is affected by the separation flow,the distribution of the inner and outer flow field is extremely uneven,the inner flow velocity is higher while the outer flow velocity is lower,and an obvious low-velocity zone appears at the inner side,resulting in a local eddy current.Besides,a complex secondary flow is also generated in the air duct.The superposition of mainstream flow and secondary flow intensifies the disorder of the air flow in the air duct,causing an unstable flow of the impeller inlet After installing a double circular arc guide vane in the 900 bend,the uniformity of the mainstream flow in the air duct is improved,the secondary flow intensity is significantly reduced,the low-velocity zone is basically disappeared,and the disordered area at the inlet of the impeller is significantly reduced.In order to obtain a reasonable and effective arrangement of the guide vanes in the 900 bend,and to obtain more uniform and stable inlet conditions at the inlet of the impeller,we numerically analyze the influence of different parameters on the flow field in the intake duct and parameters include the number of installations,arrangement,starting and ending positions,central angle,tail length and installation angle.The results show that flow separation can be better suppressed when four guide vanes are arranged in the radial direction according to the position of s=1,2,4,7(equal interval),making the flow field in the bend more uniform.The arrangement of the guide vanes near the downstream of the bend section makes the inlet velocity of the impeller more uniform,and the pressure loss generated in each cross section of the air channel is also smaller.With the increase of the central angle of the guide vanes,the flow velocity of the impeller inlet tends to be stable.The stability of the velocity field can be improved when the first and fourth guide vane is extended by 150mm each and the low tail effect caused by the extension of the guide vane can be eliminated.When the installation angle of the inner two guide vanes is 5°and the outer is 0°,the uniformity of the inner and outer air flow can be improved,and the airflow at the inlet of the impeller can be more stable.The research results of this paper can provide a theoretical basis and engineering reference for improving the inlet condition of the fan impeller,and thus ensuring the safe and reliable operation of the fan. |
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