Research On Performance Optimization And Flow Field In Small Flow Of Contra-Rotating Fan In The Early Stage Of Operation

The contra-rotating axial flow fan has the advantages of compact structure and high efficiency,it has been widely used in the ventilation system of large coal mines.In the actual production of coal mine,the ventilation capacity is usually considered in the middle and late period of the mine mining,so the fan has more energy in the early stage of production,and the ventilation capacity of the fan is not matched with the actual demand,so the performance of the fan needs to be adjusted.And in the early stage of production,when the fan is not properly adjusted,it is easy for the fan to operate under its small flow condition,which has the problems of low efficiency and hidden danger.Starting from the basic theory of axial flow fan,this paper aims at ensuring the rational ventilation of the mine and improving the operation reliability and efficiency of the fan,and based on the experimental data,the influence of the different regulating modes of the fan on the fan’s energy parameters in the early stage of the mine production is studied,furthermore,the flow field of fan under small flow condition is studied by numerical simulation,all of these can guide the performance adjustment of mining contra-rotating axial flow fan.And when single stage operation and reducing the number of blades are commonly used for adjusting the axial flow fans in the early stage of coal mine production.The performance of the fan can be changed well by adjusting the blade installation angle,and the maximum efficiency can reach 81.66% near the best angle.When the fan runs at a small angle,the flow and efficiency decrease obviously,the highest efficiency is only 62.87% atβa=25°/20°,and the wind pressure is still high,which can be supplemented by throttling way,but it will make the fan running economy worse.And when the fan is operated at a single stage and the blade installation angle is reduced,the pressure drop is about 2/3,the efficiency is about 60%,the economy is basically guaranteed because of the half of the power,and it can be applied to the operation condition of the early stage of the mine production.When the blade number of the fan is reduced and the blade installation angle is reduced,the flow and pressure of the fan are reduced obviously,which is in line with the operation requirements of the early stage of the mine production,and the decrease of efficiency is not obvious,the maximum efficiency can still reach 77.57% and the comprehensive performance is superior whenβa=37°/32°.And when the fan operates under the small flow condition,the pressure on the blade pressure surface becomes larger and the pressure is higher to the top of the blade,making the air flow impact on the top of the blade gradually increasing,the air flow separation on the suction surface is gradually aggravated and the air flow angle changes,what’s more,the pressure gradient increases,and the gap between the sides of the top of the blade is constantly changing,causing the leakage at the top clearance of the blade was aggravated.Therefore,in the early stage of mining,the method that only adjusts the angle of blade installation can not achieve economic and reasonable ventilation.It is better to meet the low requirements for the flow and wind pressure in the early laneway,and the adjustment method of reducing the number of blades or the single stage operation of the fan should be supplemented.And when the fan runs at low flow rate,the performance will decrease obviously,and the fan may enter the unstable working area,which has great harm,it is necessary to regulate the fan according to demand in time,so as to avoid the fan running under the condition of small flow.