| The phenomenon that the centrifugal pump operated at gas-liquid two-phase flow conditions often occurred in the engineering practice.The existence of the gas in the working medium has obvious influence on the performance of the centrifugal pump.The operating characteristics of the centrifugal pump will change greatly in gas-liquid two-phase flow condition.The phenomenon will produce severe vibration problem,and even surge which will seriously affect the reliable operation of the system.Therefore,it is of great theoretical and engineering application to study the internal flow mechanism and flow induced characteristics of the centrifugal pump in the condition of gas-liquid two-phase flow.In this paper,based on the experimental and numerical simulation methods and combined with the existing research and flow theory analysis,performance characteristics test and the dynamic performance test such as pressure pulsation and vibration test were carried out at different rotation speed under different inlet gas volume fraction.Based on the Euler inhomogeneous flow model,steady and unsteady numerical simulation were carried out to analyze the internal flow field of the model pump in the gas-liquid two-phase flow condition.The main contents and results are as follows.1.The study status of the internal flow characteristics of pumps in gas-liquid two-phase conditions were summarized in three aspects: basic theoretical study,experimental study and numerical study,then the lack of the current study were put forward.At last,the significance of the study on the internal flow characteristics of the pump was described.2.The centrifugal test rig in the gas-liquid two-phase flow condition was set up and performance characteristics tests were carried out at different rotation speed in different inlet gas volume fraction,the following conclusions were drawn from the data processing analysis.In gas-liquid two-phase conditions,when the inlet gas volume fraction is higher than 1% in the small flow conditions(? <0.04),the performance of the pump will decline sharply,and the operation range will be reduced with inlet gas volume fraction increased.The gas has a more obvious influence on the performance of the pump in the low speed and low flowrate condition.The theoretical head is independent of the density of the conveying medium when the inlet gas volume fraction is lower than 8%.When the inlet gas volume fraction is less than 3%,it is also found that the law of rotational speed similarity could still be established.3.Based on the LMS test system,the dynamic performance test of the model pump in different inlet gas volume fraction conditions was carried out to obtain the unsteady pressure pulsation and vibration spectrum characteristics in different working conditions.The following conclusions were drawn.The pressure signal and vibration signal obey the normal distribution.When the inlet gas volume fraction exceeds 5%,it is found that the amplitude of the pressure fluctuation in low frequency zone obviously increase.With the increase of the inlet gas volume fraction,the overall amplitude of the vibration signal will increase obviously,especially in the low frequency band.The vibration signal decreases first and then increases,and then decreases again.The vibration becomes the largest when the inlet gas volume fraction is 5%.When the inlet gas volume fraction is higher than 5%,the low frequency vibration energy will become an important part of the pump system vibration energy.4.Based on the Euler inhomogeneous flow model,the steady and unsteady numerical calculation of the model pump were carried out in different flow rates and different inlet gas volume fraction conditions.The following conclusions were drawn.When the inlet gas volume fraction is more than 3%,the initial bubble diameter is an important factor to be considered to do the calculation.With the increase of inlet gas volume fraction,the gas has the tendency to move along the suction surface to the exit side.To some extent,air can improve the reverse flow condition at the inlet part of impeller.The aggregation of the gas phase in the impeller has a great relationship with the generation of the vortex.When the inlet gas volume fraction increased to 3%,the amplitude of the low frequency region will increase slightly and the broadband pulse will be generated,and the range of the broadband fluctuation will be widen with the inlet gas volume fraction increased.The higher the inlet gas volume fraction is,the more obvious the influence on the broadband pulse is. |
PDF Full Text Request