| Multi-blade centrifugal fans with high pressure coefficient,small flow coefficient and small size factor are widely needed in some special applications.However,due to the structural characteristics of the fan itself,the mutual restriction of high pressure and small flow rate is a difficult problem in the study of multi-blade centrifugal fan with high pressure ratio and small flow rate.As an important auxiliary part of the fan,the collector plays the role of guiding the air flow uniformly into the fan.The design of the collector determines the air flow status in the fan.In this paper,multi-blade centrifugal fan with high pressure ratio and small flow rate in gas water heater is taken as the research object.Because of the unreasonable structure of the fan collector,the flow in the front disc of the impeller is chaotic and the flow separation phenomenon is serious.Combined with the CFD method,the influence of the structure parameters and its installation position on the multi-blade centrifugal fan is studied in this paper,which is to improve the internal flow state and the aerodynamic characteristics of the fan.Specific contents of this paper are as follows:(1)The numerical simulation of the flow in the original multi-blade centrifugal fan is carried out,and the calculation results are basically consistent with the experimental data,which verifies the reliability of the numerical simulation method.Due to the unreasonable design of the fan inlet collector,the airflow entering the fan is turbulent,and the internal pressure and velocity distribution of the fan are not uniform,especially in the front plate area of the impeller.The flow separation in the front plate area of the impeller is severe,and the blade channels are filled with the separation vortex to block the flow.Reflow occurs in the impeller blade area near the volute tongue,reducing the efficiency of the impeller work and the aerodynamic performance of the fan.(2)On the basis of controlling the air volume of the fan,the influence of the collector structure on the fan is studied.The influence of collector shape on fan aerodynamic characteristics and internal flow was investigated.The velocity vector diagram of fan shaft section and P-Q performance curve were analyzed.The results show that the circular inlet is more suitable with the requirement of high pressure ratio and small flow rate of gas water heater than the annular inlet.The orthogonal experimental design method is adopted for the arc-shaped collector.The radius of the arc,the length of the collector and the inlet diameter of the collector are used as the optimization parameters.The total pressure of the fan is the optimization goal.The order relationship of factors and optimal parameter combination schemes affecting the total pressure of the fan are obtained.The results show that the optimized fan increases total pressure and efficiency.(3)The eccentric design of the fan current collector is proposed,and the influence of the installation position of the current collector on the flow and performance in the multiblade centrifugal fan is studied.The simulation results show that the optimal deviation scheme of the current collector is effective for improving the full pressure and full pressure efficiency of the fan.Compared to the original fan,the total pressure of the optimized fan is increased by approximately 40 Pa and the total pressure efficiency of the optimized fan is increased by 4.3%.It is found that the eccentricity of the collector helps to reduce the flow separation in the impeller region and improve the radial velocity distribution at the impeller inlet and outlet.This provides a reference for the future study of multi-blade centrifugal fan with high pressure ratio and small flow rate.After optimizing the structure and installation position of fan collector,the internal vortex of fan is reduced,its full pressure is increased,and its aerodynamic performance is improved.It has guiding significance for the design and application of small multi-blade centrifugal fan. |
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