| Large wheel diameter ratio forward blade is adopted in multi-blade centrifugal fan,and the number of blades is large,it’s widely used in the field of air conditioning because of its advantages of large flow coefficient,low noise.A certain type of centrifugal fan of air conditioning was taken as the research object in this paper,the total pressure efficiency of the fan under rated working conditions was taken as the target,numerical simulation of prototype and modification was carried out by using CFX software.Two-dimensional unsteady flow characteristics of centrifugal fan were investigated.Three-dimensional numerical simulation and analysis of the original fan model were carried out,and the simulation results,such as velocity,pressure,vorticity and streamline,were analyzed.The results show that the efficiency of the prototype fan is 41.04%,there is a large vortex at the outlet of the fan,and the secondary flow in the front disk of the impeller is obvious.Due to excessive oblique cutting of the volute,the boundary layer separation in the blade passage is serious.Comprehensive analysis found that unreasonable volute design will lead to lower performance of the fan.On the basis of the prototype simulation,the volute of the fan was redesigned with independent experience design method,the simulation of the modification was also carried out.The efficiency of the modified fan is 59.83%,which is 45.78% higher than the prototype.The results show that compared with the original exit vortex region,the modified scheme basically disappears,and largely eliminates the phenomenon of flow separation in impeller passage caused by excessive diagonal cutting,and the efficiency is greatly improved.Then,based on the improvement of volute profile on non-equilateral basis,the influence rules of outlet upconvex profile,straight profile and downward convex profile on fan performance were explored.It is found that in outlet profile scheme,the fan efficiency is the highest when the profile is straight,but the profile has little influence on fan efficiency.It is found that with the decrease of the expansion Angle of the outlet,the velocity distribution of the outlet surface tends to be uniform,and the low-speed area of the outlet section keeps decreasing,but the vortex intensity at the cochlea tongue increases,and the fan efficiency is the highest when the expansion Angle is 30°.On the basis of volute modification design,impeller modification design was carried out,and the influence rule of blade number,outlet Angle and inlet Angle on fan efficiency was explored successively.The final results show that: when the number of blades is 42,47 and 52,the efficiency of the fan increases with the increase of the number of blades,and the number of blades has a great influence on the efficiency.When the blade outlet Angle scheme is 149°,165° and 170°,the efficiency of the fan keeps improving as the outlet Angle increases,and the outlet Angle has a great influence on the fan efficiency.When the blade inlet Angle scheme is 72.5°,63° and 54°,the fan efficiency increases first and then decreases with the smaller inlet Angle,but the efficiency changes little.The steady and unsteady numerical simulation of a two-dimensional fan was completed,and the phenomenon of blade wake and jet flow was analyzed on the basis of the steady results.The unsteady flow characteristics of the centrifugal fan were studied by the unsteady numerical results.The results show that the throat and blade surface pressure fluctuates greatly,which is the main noise source of the fan. |
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