Study Of The Internal Flow And Noise Characteristics Of Mini-Pump For Washing Machine Under Air-Water Two-Phase Flow

This research was one of the main contents of the program for National Natural Science Foundation of China(51779107)and Senior Talent Foundation of Jiangsu University(15JDG048).Mini pumps for washing machines,an essential household appliance,are regarded as one of the prerequisites for the development of people's living standard globally.The internal flow field of the mini pump for washing machine is complex due to its compact structure and it normally adopts the upper drainage method.With the decrease in water level,the pump undergoes in the state of air-water mixture transportation period and empty discharge period at the end of drainage,and produce unsteady flow.This unstable flow not only results in the deterioration of pump performance but also induces larger vibration and noise,which could lower the user experience and harm the acoustical quality of the washing machine.In addition,the concept of green home appliances is popular.This means the users and the market would put forward higher requirement on the quality of the washing machine.Therefore,the study on the flow induced noise of the drain pump for washing machine is of theoretical significance and engineering value.The mechanism of the flow-induced noise was discussed at first.Then,pump performance test was processed under pure water as well as under different inlet air volume fraction at part load conditions.Then the test of the model pump and the numerical simulations were carried out to study the internal flow and the flow induced radiated noise of the model pump in order to deepen the understanding about why the drainage pump stop working during air-water mixture transportation period and to improve the performance of the drainage pump.The following research objectives were mainly involved:1.At First,the dissertation introduces the research background on the internal flow field as well as analyze the noise sources in washing machine mini pump and general centrifugal pump.Then,in order to examine the hydraulic performance and acoustic characteristics,the test bench for prototype pump model has been setup in a sound proof room(semi-anechoic chamber).The performance characteristic experiment of the model pump showed that the head drop slowly with the increase of the flow rate and the pump exhibits low efficiency.But the efficiency of the model pump is in good agreement with the value recommended by the manufacturer.In addition,this research also includes the external characteristics experiment of two-phase flow under four different flow rates by the addition of different inlet gas contents into the pump with the help ofcompressor.The flow head descending curve shows a reasonable decline with respect to different air volume fraction and different flow rates.Further,the noise experiment showed that the running cycle of the model pump would be divided into three stages: start-up period,normal drainage period and the empty discharge period.And the level of the noise during the empty discharge period is higher than that of the normal drainage period because of air-water two phase flow.Further,the frequency domain analysis also showed the higher values of sound pressure level in empty discharge period compare to normal drainage period.2.The numerical simulation based on performance experiment and radiated noise experiment was carried out in order to study the internal flow field of the model pump in pure water condition(normal drainage period)and in air-water two phase flow condition(empty discharge period).The head results obtained in pure water condition shows a reasonable agreement between the simulated and experimental value and the pump exhibits the maximum simulation efficiency of 21.07% at design flow rate.Moreover,the internal flow field of pure water is calculated based on two different turbulence models(k-omega and k-epsilon)and the internal flow field of two-phase flow is calculated using heterogeneous flow model under different inlet air content and part load conditions.The results of internal flow and gas phase distribution are obtained under four flow rate conditions.The results show that the influence of gas on the drainage pump is smaller when the gas content is 1%.As the gas content increases,the slope of the flow-head descending curve becomes larger,and the influence of gas content on pump performance starts increasing as the flow rate condition changes from design to the lowest flow rate.Further,when the gas content increases between 1-2%,a sudden decrease in head happened and the head descending curve becomes more irregular for all flow rate conditions.In addition,under the lower gas content condition,the gas accumulation first appears near the blade region and the back of the blade,which is affected by the peripheral pressure gradient in the impeller flow channel.As the inlet gas content increases,the bubble gradually develops into a larger air packets and blocks the impeller flow channel,which in turn weakens the function of the drain pump.