| Axial flow fans are widely used in various sectors of the national economy and are indispensable in many fields including tunnels,textiles,mines,construction,etc.,which also brings great demand for electricity.Among them,the counter-rotating axial flow fan is widely used in the ventilation of subways,tunnels and mines because of its compact structure,large flow rate,low noise and good inverting flow performance.However,the internal flow of the counter-rotating axial flow fan is extremely complicated,which will cause a large energy loss and reduce the efficiency of the fan.Therefore,optimizing the structure of the fan to improve its efficiency is important for saving resources and improving safety.The research object of this paper is a counter-rotating axial flow fan with mounting angle adjustable rotor blade by a fan factory in Zhejiang,and the two-stage blades of the fan are lofted and thickened by 16 different airfoil curves distributed at different blade heights.The full-flow field numerical simulation of the counter-rotating axial flow fan is carried out by using CFD technology.The matching relationship between the two-stage blade installation angle,the two-stage impeller speed and the fan performance is studied.Finally,through the modification of the fan blades,the goal of improving the efficiency of the fan is achievedThe main contents and results of this dissertation are divided into the following three aspects:(1)Studied the matching mechanism between the front-stage blade mounting angle and the overall performance of the counter-rotating axial flow fan.The results show that the performance curves of the fan shift with the change of mounting angle of the front-stage blade,and the optimal efficiency point shifts to the left within a certain range with the decrease of the mounting angle.During the operation of the fan,selecting the appropriate mounting angle according to the current mass flow condition can effectively improve the aerodynamic performance and the distribution of various flow parameters of the fan,at the same time,the flow loss will be impaired.What's more,the working range is expanded,and it will delay the occurrence of stall and surge by improvement.(2)Based on the efficiency and total pressure of the fan,the optimal matching relationship between the two-stage impellers speeds and the blades installation angle under different working conditions was studied by orthogonal optimization method.The results show that choosing the right matching relationship can keep the fan working at a high performance level at all operating points.Compared with the original model,the average efficiency of optimized fan at each flow points is 12.80%higher than that of the original fan,and the average total pressure is increased by 24.22%.(3)The fan was modified according to the change of working condition.Then,the front-stage blade was optimized by orthogonal optimization method according to the pressure distribution of the blade surface.The research shows that the efficiency of the optimized fan has increased by 0.5%,and the total pressure has increased by 26Pa.Compared with the original fan,the pressure distribution and the load distribution in the front-stage blade surface of the optimized fan are more reasonable.The optimized method not only reduces the tip clearance leakage and radial velocity of the front-stage impeller but also optimizes the vorticity and turbulent kinetic energy distribution at the blade tip,thereby reducing the flow losses and improving the efficiency and total pressure. |
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