Study And Analysis On Flow Behavior In Counter-rotating Variable-pitch Axial Flow Fan

Counter-rotating variable-pitch axial flow fan is composed of two fan units with the same structure in series.Each fan unit has a separate impeller drive motor and blade angle adjusting mechanism.It is widely used in coal mine,subway,construction and other fields because of its large air volume,high pressure and wide performance adjusting range.By adjusting four free parameters of impeller speed and blade installation angle of front and rear stage,the counter-rotating variable-pitch axial flow fan can realize the purpose of changing fan operation state and operating efficiently under various working conditions.It is greatly significance to study the influence of operation parameters on the aerodynamic performance of fans and to explore the internal flow field characteristics of fans,so as to improve the aerodynamic performance of fans and widen the range of efficient and stable operation.In this paper,the DTF-20 counter-rotating variable-pitch axial flow fan provided by the cooperative enterprise is taken as the research object.The flow field characteristics of the fan under the conditions of internal interference,different speed matching,different blade installation angle and casing treatment are analyzed by numerical simulation.The main research contents and achievements of this thesis are composed of the following four parts:(1)The flow interference law of vane-rotor and impeller-vane clearance of counter-rotating variable-pitch axial flow fan was studied.The results show that the potential flow interference between the front guide vane and the impeller gradually develops from the tip to the root of the blade,and there is a weak wake interference effect only near the guide vane.The flow field in the clearance between the guide vane and the impeller is not only affected by the wake interference of the impeller,but also by the wake superimposed by the guide vane and the impeller.(2)The effect of speed matching on the aerodynamic performance of a rotating blade adjustable axial fan was studied.The results show that the static pressure efficiency of the fan is close to that of the differential speed matching under the condition of full flow rate,which is beneficial to the efficient operation of the fan under the condition of small flow rate.The highspeed of the front stage and the low speed of the rear stage are helpful to improve the static pressure rise of the fan and the flow ability of the gas in the blade root area.(3)The influence of the installation angle of the rear stage rotor blade on the aerodynamic performance of the counter-rotating rotor blade adjustable axial fan is studied.By fixing the installation angle of the front stage blade,the numerical simulation of the rear stage fan blade at three different installation angles was carried out.The results show that under the condition of small flow rate,smaller installation angle can improve the efficiency of fan and expand stall margin;under the condition of large flow rate,the aerodynamic performance of fan with larger installation angle is better,and the range of efficient operation of fan can be widened.(4)The effects of the front and rear casing treatments on the aerodynamic performance of an adjustable axial fan with counter-rotating rotor blades were studied.The results show that the front casing treatment has a great influence on the aerodynamic performance of the fan.Under the condition of small flow rate,the front casing treatment can improve the load of the rear impeller motor,effectively improve the static pressure efficiency of the fan,expand the stall margin,and expand the stable working range of the fan.