Numerical Simulation Of Internal Flow Field In Tip Clearance Of Gas-liquid Multiphase-pump

The flow in the tip clearance of the gas-liquid multiphase-pump is of much importance for the hydraulic performance of the whole pump.Small clearance can improve the performance of the pump,while too large clearance can easily lead to the decline of pump performance,the enhancement of pressure pulsation,the aggravation of vibration,and even affect its operation stability.Therefore,it is of great significance to study the internal flow field in the tip clearance of the gas-liquid multiphase-pump.In this paper,the gas-liquid three-stage multiphase pump with rotating speed n of 3500r/min and flow Q of 36.6m3/h is taken as the research object.By changing the blade width,four blade tip clearance schemes are obtained:0 mm,0.5mm,I.Omm and 1.5mm.Using ANSYS-CFX software and SST k-? turbulence model,the internal flow field of the second stage impeller was studied under the conditions of 0,5%,10%,15%and 20%gas fraction.Through the analysis of the numerical simulation results,it is found that:(1)The larger the tip clearance is,the smaller the pressure rise and efficiency are.With the increase of gas content,the pressure rise and efficiency decrease more obviously.When the gas content is 15%,the pressure rise and efficiency decrease by 8%and 3%respectively when the tip clearance is 1.5mm.(2)The streamline distribution of the TIP0 impeller is more even,the flow velocity at the inlet and outlet of the 2nd impeller is faster(about 15m/s)and the streamline is dense,the streamline is mostly concentrated on the pressure surface,the streamline on the suction surface is sparse,but the flow velocity on the suction surface is higher(8?14m/s);when the tip clearance increases,the flow field becomes disordered,and there is a high-speed gap jet phenomenon at the tip clearance,and the flow velocity at the gap is more than 15m/s On the other hand,larger gap means the longer distance,higher velocity,larger jet area,lower flow velocity in the channel,the more sparse the streamline on the suction surface,the more concentrated the streamline on the pressure surface,andat the outlet the smaller high velocity area;with the increase of air content,the streamline of the TIP0 impeller becomes more disordered,and the more obvious the gap jet phenomenon,especially at the trailing edge of the blade;at the same time,the flow field of the blade increases Especially at the exit,the streamline becomes sparse and the area of high velocity area decreases.(3)In the TIP0 impeller,when the air content is between 0%and 10%,there is a low speed zone in the front and middle section of the pressure surface.This is because in the TIP0 impeller,the front section of the blade is blocked,resulting in liquid separation,flow disorder and low speed.However,with the increase of the air content,when the air content is between 15%and 20%,the large low speed zone gradually moves to the suction surface,and the whole flow channel decreases.In the open impeller,the low speed zone gradually moves to the suction surface With the increase of tip clearance,the range of low speed region is gradually narrowed,but the flow velocity of the whole passage is reduced.(4)For TIP0 impeller,the change range of air content is the largest,the gas content at the inlet is more than twice that at the outlet,while the open impeller changes more smoothly,and with the larger clearance,the smaller the change range.The increase of blade tip clearance will lead to the gas gradually spreading to the outlet and the position of suction surface mainly concentrated;and with the increase of gas content,the larger the gas accumulation area will increase,and the gas content at the outlet will hinder the energy exchange between the pump and the fluid,which will lead to the decrease of pump head and worsen the performance of the pump.(5)The pressure coefficient of the monitoring point is smaller at the inlet.The pressure coefficient gradually increases from the inlet to the outlet,and reaches the maximum at the outlet.The pressure slightly changes at the inlet,and the closer the pressure changes,the greater the pressure changes.Because the impeller inlet has a large flow loss due to gas blockage and backflow,so the pressure here is lower and the change is small.Under the condition of 15%gas content,the pressure fluctuation trend of each monitoring point of impeller is basically the same.In the second stage impeller of mixed transport pump,the number of blades is 4,and the dominant frequency of most monitoring points is 408.31hz,which is 7 times of the rotation frequency.This is caused by the interference of dynamic and static,so the dominant frequency is affected.