Study On Stall Inception Mechanism Of Coal Mine Contra-rotating Main Fan Under Inlet Distortion

With the continuous improvement of the requirements on the range of operating conditions,operating stability and safety of the main fan equipment in coal mine,the aerodynamic instability of the mine main fan under low flow rates is becoming more and more prominent.When some factors such as inlet distortion cause the fan to run in the near-stall condition,it may cause safety accidents such as blade crack or even fracture,which will bring serious situations to the coal mine.Without in-depth and meticulous research on this,the stability and safety of fan operation cannot be guaranteed,nor can it satisfy the needs of the current intelligent mine construction.Therefore,on the basis of systematically summarizing and referring to the existing research achievements in aero-engine and related fields at home and abroad,this thesis carries out the study on the mechanism of stall inception and its propagation and development in coal mine contra-rotating main fan under the condition of inlet distortion.It can not only provide theoretical basis for stall prediction(avoiding the occurrence of stall)and implementation of active control in coal mine main fan operation,but also lay theoretical foundation for improving the aerodynamic stability of the fan in the design stage,so it has important theoretical significance and engineering value.In the thesis,a coal mine contra-rotating main fan for forced type ventilation is taken as the study object.Firstly,the unsteady flow characteristics and performance of the fan under three inlet conditions(uniform inlet,elbow inlet distortion and complex inlet distortion)are analyzed numerically.Then,the study focuses on the uniform inlet and complex inlet distortion conditions.The DES(Detached Eddy Simulation)technique and outlet throttle valve model are applied to the numerical simulation of unsteady flow in the full flow passage of the fan.Based on numerical analysis,the location of the stall inception disturbance initially occurred in the fan and the type of the stall inception disturbance are obtained under near-stall conditions with low flow rate;the generation mechanism,propagation and development of the stall inception disturbance are revealed under different conditions according to the unsteady flow field characteristics of the fan;Under the inlet distortion condition,the dynamic evolution processes of tip clearance leakage flow for the two impellers are simulated,the suppression ability of contra-rotating impellers to the downstream propagation of stall disturbances is explores,and the influence of the development of the stall vortex on the radial and axial flow fields of the contra-rotating fan is investigated.The results show that under the two kinds of distorted inlet conditions,the stall inception disturbances of the two impellers of contra-rotating fan all occur in the tip region of the blades.Under the uniform inlet condition,the stall inception phenomenon occurs firstly in the front stage impeller,while under the complex distortion condition,the stall inception phenomenon occurs firstly in the rear stage impeller.The stall inception in the front stage impeller is"spike-type",and the stall inception appears with the emergence of "leading edge overflow" and"trailing edge backflow",and the stall inception in the rear stage impeller is also "spike-type".Although low-speed disturbance exists in the region near the blade root of the rear impeller,the low-speed disturbance and disturbance in the blade tip region are formed independently.The disturbances eventually merge and develop near the trailing edge of the blade suction surface.Although the occurrence and development of the stall inception in the contra-rotating fan under the uniform inlet and complex inlet distortion conditions are similar to some extent,the sequence of the stall inception disturbances in the two impellers,the degree and range of the influence of the stall vortex on the internal flow field of the fan are different.Compared with the uniform inlet condition,the occurrence of the stall disturbance in the contra-rotating fan is slightly earlier under the complex distortion condition,the size of the vortex cores in blade channels is larger,the distribution range is wider,the influence of stall vortex on radial and axial flow fields is more significant,and the fluctuation of the airflow in the fan is stronger.