| As one of the most important environmental protection tool in modern times,although the cleaning sweeper vehicle does bring clean environment,it causes serious noise pollution and energy waste,which violates the policy of building a resourceconserving and environment-friendly society.On account of this,optimization and development of high efficiency pneumatic conveying system has been listed as a key research and development project in "New energy vehicles" key special project 6.2 of the 13 th five-year national key research and development plan.Pneumatic conveying system is mainly composed of centrifugal fan,dust collector,dust container,pipeline and air flue.Among them,centrifugal fan and dust collector are the main noise sources,and the aerodynamic noise produced by them accounts for the majority of the vehicle noise.Thus,reducing the aerodynamic noise of both will reduce the vehicle noise effectively.In addition,due to complex structure of pneumatic conveying system,a lot of energy will loss when it works,and it will affects the working efficiency of cleaning sweeper vehicle seriously,so it is very important to reduce the pressure loss of each component.In view of this,the pneumatic conveying system has been optimized from the following aspects.(1)The aerodynamic noise of centrifugal fan was optimized.Based on Fluent software and FW-H acoustic analogy model,the aerodynamic noise of centrifugal fan was calculated.Firstly,a new kind of volte side plate structure with inclined and stepped shape was designed in this paper,and then the comprehensive influence among side plate’s tilt angle,volute width and volute tongue radius on the aerodynamic noise of the fan was mainly focused on.Based on MATLAB software,polynomial fitting was used to establish the function relations between fan efficiency and three parameters,between total pressure and three parameters,and between total sound pressure level and three parameters,and then the objective functions were optimized by using multi-objective optimization genetic algorithm.The numerical results show that: the side plate’s tilt angle has the most significant influence on aerodynamic noise,and between 0° and 6°,the noise can be reduced by 0.6d B for every one degree increase of the side plate’s tilt angle.Moreover,the total sound pressure level of the fan can be reduced by 8.7d B through decreasing the width of volute,increasing the radius of volute tongue and increasing the side plate’s tilt angle reasonably while keeping the aerodynamic performance of the fan basically unchanged,and the base frequency noise,double frequency noise and triple frequency noise were reduced by 11 d B,18.2d B and 7d B respectively.Consequently,the effect of noise reduction is obvious.(2)The aerodynamic noise of dust collector was optimized.Based on Fluent software and FW-H acoustic analogy model,the aerodynamic noise of dust collector was calculated.Firstly,a shoulder structure was added to the dust collector,and the comprehensive influence between shoulder angle and inclined angle of upper wall on the aerodynamic noise of the dust collector was mainly focused on.Based on MATLAB software,polynomial fitting was used to establish the function relations between dust collector’s total pressure and two parameters,and between total sound pressure level and two parameters,and then the objective functions were optimized by using multiobjective optimization genetic algorithm.The numerical results show that: the shoulder angle has a significant influence on aerodynamic noise,and between 0° and 20°,the noise can be reduced by 0.4d B for every one degree increase of the shoulder angle.Moreover,the aerodynamic noise of the dust collector can be reduced effectively by increasing the shoulder angle reasonably while reducing the energy loss of the dust collector,and the maximum reduction is 6.2d B.(3)The aerodynamic performance of dust container was optimized.Based on CFX software,the influence of distance between baffle and outlet of air intake pipe on air flow was discussed firstly,and then the airflow distribution in the dust container under different values was comprehensively compared.Finally,H=200mm was selected because the pressure loss was minimal.On this basis,the influence of baffle’s tilt angle on airflow distribution was discussed too.Research show that: the intensity of vortex will decrease obviously when the tilt angle of baffle increased,therefore,γ=6° was determined.In order to make the dust particles have enough settling space and settling time,most dust-containing airflow should flow into the tail of dust container after being drained by the baffle.In view of this,the shrink angle of baffle was further optimized,and φ=140° was determined according to the principle that the lower velocity is,the better settlement becomes.The numerical results show that: the pressure loss of the optimized dust container can be reduced by 14%,and the aerodynamic performance can be improved while the energy is greatly saved.To sum up,through optimizing the key components of the pneumatic conveying system,the overall aerodynamic noise of the pneumatic system was reduced by 5.9d B,the pressure loss was reduced by 17%,and thus the working performance of the pneumatic conveying system has been improved comprehensively.In conclusion,the aerodynamic noise of the fan can be effectively reduced by decreasing the width of volute,increasing the radius of volute tongue and increasing the side plate angle reasonably while keeping the aerodynamic performance of the fan basically unchanged.The volte side plate structure with inclined and stepped shape can make the pressure pulsation reach the wall of side plate at different times,and it will produce a phase difference.As a result of that,the interference caused by noise in the process of reflection and propagation will be effectively reduced.The aerodynamic noise of the dust collector can be reduced effectively by increasing the shoulder angle reasonably while reducing the energy loss of the dust collector.Also,the pressure loss of dust container can be effectively reduced by adjusting the distance between baffle and outlet of air intake pipe,and the intensity of vortex near the baffle can be reduced by increasing the tilt angle of the baffle. |
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