Research On Contra-rotating Auxiliary Fan Based On Blade Pitch Adjustment

With the increasing depth of excavation,coal mine will form a complex multi-zone ventilation system,and emerge a large ventilation resistance,insufficient mining site wind,low efficiency and other issues.Long-distance underground ventilation often uses a high-power auxiliary fan with a large diameter high-strength pipe,and ventilation distance can reach 2000 m above.However,contra-rotating fan is not able to run efficiently during whole excavation.If the fan doesn’t work under the design condition for a long time,not only results in waste of energy,but also affects the operation place.So,adjusting the auxiliary fan according to the conditions of the ventilation system is needed.Therefore,the study of blade pitch’s influence on fan’s performance and flow field has very important significance in achieving high efficiency operation.FBD No8.0 2×55kW auxiliary fan is simulated by using computational fluid dynamics software Fluent.The impact of first and second impeller’s blade pitch on fan performance is explored,and performance curves of different blade pitches are drawn.The simulation results are verified by experiment;the different results between different blade angle changing method are compared.It gives basis to choose the reasonable option for efficient operation of the fan and to avoid motor overload.Research shows that while increasing pitch of both stages,the total pressure curve shifts to the right,efficiency of large flow conditions improves and shaft power increases as well.Although they are more matched,the growth rate of the second stage load is greater than the first;by changing pitch of the blade is able to meet the needs for efficient operation under different conditions,changing same pitch in different impeller could lead to similar performance,while operating efficiency is greatly influenced by the second stage;and the second stage of blades’ pitch changes while the load of the first stage is not affected.If changing the pitch of the first stage,the first stage shaft power changes,the second stage will be increased or decreased as well.Also,regarding the tunnel length of 500 m and 2000 m as short-distance and long-distance ventilation representatives,it is analyzed combined with two different pipe network characteristic and different pitch’s performance curves.When tunnel is short,air quantity and pressure required is smaller,small pitch of the blade can effectively reduce the output power,saving energy consumption;when tunnel is long,harmful gases emission increases,the resistance of pipe also increases and larger air quantity and pressure is required,it is possible to make the fan work in the non-stable area,so increasing the pitch appropriately could meet the demand pressure and high flow of working site.However,an increasing angle may lead to the motor overload.Adjusting according to the working conditions could achieve efficient operation of the fan and the purpose of energy saving.An external single motor adjustable contra-rotating fan is put forward.On the one hand,a device is used to accomplish blade pitch adjustment on the purpose of compact and easy to adjust and maintain.On the other hand,dual-motor driven mode is optimized,the use of a single power transmission gearbox to the two impellers could effectively solve the problem of poor maintaining condition and shaft power mismatching.Combining ADAMS,the blade adjustment device multi-body dynamics simulation is researched,the law of regulating blade and other corresponding kinematics are also studied to lay the foundation for further study and improvement.The adjustment ranges are-18 ° to 10 ° and-5.5 ° to 5.5 °,and transmission ratio is not constant.