| With the advantages of high efficiency and high flow rate,the variable-pitch axial flow fan has been widely used for induced draft fan and primary fan in large-scale power plant.The guide vane acts as a link between the preceding and the following,and rotor blade or diffuser is introduced in the future by improving internal flow and reducing flow loss,and its own structure will directly affect the overall performance of the fan.The study of guide vane has important reference value for improving the performance and static structure of the variable-pitch axial flow fan.In this thesis,numerical simulation technology is adopted to simulate the fan in three dimensions after the length,number of guide vane and installation angle of guide vane changed,and the flow field results are obtained.Static analysis and vibration analysis are carried out on the fan blade by combining the fluid-solid coupling analysis method.Results reveal that an apparent impact of the different schemes of long-short composite guide vanes is observed;the total pressure and efficiency of fan with composite guide vanes reducing trailing length of 10% and 20% are increased at lower flowrate,while manifest the opposite variations at large flow rate;fan performance under other cases is inferior to the original fan,and the performance with the guide vanes reducing trailing length is better than to that reducing leading length;the total pressure distribution on the second blade surfaces with the guide vanes reducing trailing length of 10% is varied and the work capability is enhanced,whereas the entropy production rate is augmented compared with the original fan under design condition.The stress and the total deformation of the second blade are to some extent increased and the vibration is weakened,but still meet the operating requirements;the performance of the fan with reduced guide vane is higher than the original fan,whereas the fan performance with increased guide vane is not necessarily improved;the optimal scheme is 21 number of guide vane in two stages;the full pressure rise and efficiency is increased by 119 Pa and 0.4 percentage point at rated condition;the work ability of the second stage rotor and diffusion performance of the second stage guide vane are enhanced,the change of guide vane number has a significant effect on the downstream flow field and a marginal effect on the upstream flow field;the circumferential distribution of acoustics in the second stage is more uniform than the original fan and the noise minimum is reduced by 5 d B;the total pressure rise with negative deflection of the guide vane installation angle is better than the original fan,and is improved with the increasing installation angle under the same flow rate,while manifests the opposite variation for the positive deflection of guide vane installation angle.The efficiency with negative deflection of the installation angle is slightly lower than the original fan.For the scheme of positive deflection,the efficiency is promoted at low flow rate compared with the original fan,whereas is deteriorated at large flow rate,especially the obvious reduction of efficiency is observed with increasing flow rate.For the scheme of negative deflection,the total pressure distribution on the rotor blades is varied significantly and the blade work ability is obviously enhanced.The entropy generation rate in the second-stage rotor blade and guide vane is augmented to some extent.The distributions of the equivalent stress and total deformation of the second-stage rotor blade keep unchanged,but the maximal values are raised,and the natural frequency of rotor blades is reduced slightly. |
