Study On The Aerodynamic Performance Optimization And Internal Flow Characteristics Of A High-speed Centrifugal Fan For Vacuum Cleaner

As the core power component of vacuum cleaners,the working characteristics of high-speed centrifugal fans directly affect the performance of the product.The main characteristics of centrifugal fans used in vacuum cleaners in daily life are low flow rate and high speed.The large curvature of the blades can easily cause the flow separation and blockage in flow passage.This phenomenon has a great impact on the working performance,stability,and reliability of the vacuum cleaners.Therefore,this paper takes the high-speed centrifugal fan for vacuum cleaners as the research object,and carries out the research on its internal flow structure and unsteady characteristics through numerical simulation calculation,and optimizes the blade design with the goal of static pressure efficiency to suppress flow separation,thereby improving the aerodynamic performance of the centrifugal fan.The main research work is as follows:The numerical simulation on the internal steady flow of high-speed centrifugal fan under different flow rates is carried out.Qualitative and quantitative analysis is investigated from the perspectives of pressure,velocity,streamline,and turbulence energy.The research shows that the velocity distribution at the impeller outlet position is uneven under the Q_n operating condition.As the flow rate decreases,flow separation will first occur at the trailing edge of the suction surface in the impeller and near the wheel cover.At low flow rates,large-scale separation vortices will form in the flow channel,and there will be obvious backflow characteristics at the impeller outlet,which is the main reason for the high turbulence energy dissipation inside the impeller at low flow rates.The characteristics of unsteady flow in high-speed centrifugal fan are studied.The spatiotemporal evolution characteristics of the flow lines inside the impeller of the centrifugal fan under the 0.3Q_n operating condition are revealed.The results show that a separation vortex is easily generated at the leading edge of the suction surface of the blade,which continuously develops and expands over time.The vortex drives downstream fluid to form a vortex opposite to the rotation direction,blocking the outlet and causing backflow.At the same time,the spatiotemporal evolution law of the internal vortex structure of the impeller constantly shedding,recombining,developing,and disappearing under low flow rate is explained.The pressure pulsation characteristics under different flow rates are analyzed in detail,revealing the periodic phenomenon of pressure pulsation under the Q_n operating condition,and the frequency domain distribution is mainly dominated by the multiple rotational frequency and blade frequency.It is established that the pressure pulsation phenomenon under the 0.3Q_noperating condition is closely related to the impeller rotation,vortex structure,and outlet backflow.The optimization method of blade profile in centrifugal fan based on Bezier curve is established.The influence of the blade outlet angle and the central angle on the external characteristics of the centrifugal fan is explored.The numerical results show that within a certain range,increasing the blade outlet angle will reduce the static pressure efficiency of the fan while increasing the static pressure;increasing the blade central angle can effectively improve the static pressure efficiency of the impeller while affecting the peak point of static pressure efficiency.A mathematical model is constructed between the blade outlet angle,central angle,and target static pressure efficiency through polynomial fitting method,and the feasible direction method is used to obtain the optimal static pressure efficiency of the centrifugal fan.The optimized model is obtained,and the static pressure efficiency is improved by 4.17%compared with the rated operating condition of the original model.The aerodynamic performance and the characteristics of internal flow in high-speed centrifugal fan before and after optimization are explored.The distribution characteristics of pressure,velocity,streamline,and turbulence energy inside the impeller and diffuser are analyzed.The results show that after optimization,the internal pressure distribution of the centrifugal fan is more uniform,the flow structure is smoother,and energy dissipation is reduced under rated conditions.However,the difference in internal flow characteristics of centrifugal fan under low flow rate is relatively small,and the centrifugal fan can reduce flow separation after optimization.The influence of impeller optimization on the distribution characteristics of internal pressure pulsation in the fan is revealed.The results show that the optimized centrifugal fan can effectively reduce the main frequency amplitude of pressure pulsation inside the impeller and the root mean square of pressure pulsation in the circumferential direction at the impeller outlet under Q_n conditions.At the same time,it can effectively suppress the interference of the impeller at the diffuser inlet,thereby improving the static pressure efficiency of the centrifugal fan.The optimized fan can effectively suppress the signal of pressure pulsation frequency domain at 0.3Q_n conditions.