Study On Flow Characteristics Of High Speed Centrifugal Pump Based On Gas-liquid Two-phase Flow

High-speed centrifugal pumps based on gas-liquid two-phase conditions are widely used in petroleum,chemical and other engineering fields.Under the mixed flow of gas-liquid two-phase medium,gas phase changes will bring different degrees influences of stability and hydraulic characteristics to the operation of centrifugal pumps.The factors affecting the gas-liquid two phases are often not single,independent,but dependent.When the parameters of the factors change,the corresponding flow characteristics will change,and will accompany the vibration,and even will block the impeller flow channel circulation,which cause damage to its equipment.Therefore,it is especially important to explore the influence of different factors on the internal flow of high-speed centrifugal pump under the condition of gas-liquid two-phase.At the same time,it also provides important reference value for the internal flow mechanism of high-speed centrifugal pump and practical engineering applications.Based on the existing basic theory,experimental research and numerical methods,this paper elaborates on the flow theory and numerical calculation method of gas-liquid two-phase,and uses the fluid analysis software CFX to carry out the two phase of gas-liquid volume steady and unsteady three-dimensional numerical simulation.The performance changes inlet flow rates,bubble diameters and rotational speeds under different inlet gas volume fraction conditions were analyzed flow characteristics of high-speed centrifugal pumps,and the specific gas phase volume distribution and gas phase velocity flow distribution in the impeller were simulated.And set monitoring points in key components such as impeller flow path,circumferential outlet,and tongue separation,observe the pressure fluctuation law induced by the interaction of different factors,and further explore the cavitation phenomenon caused by the drop of inlet pressure,the evolution of the internal flow field under the design flow,small flow and different pressure.The main research results are as follows:(1)The higher the gas volume fraction,the greater the influence on the efficiency,head and other characteristics,and performance of high gas volume fraction of the high-speed centrifugal pump decreases at a high flow rate;under the same working conditions,the larger bubble diameter,the outer characteristics falling speed is faster;when the speed is lower than the rated speed,the optimal efficiency point is shifted to the small flow rate,the speed is higher than the rated speed,and the optimal efficiency point is shifted to the large flow rate.(2)The higher the gas volume fraction,the more densely distributed gas phase in the impeller,gradually diffuse from the impeller inlet to the outlet,and gradually fill the entire flow channel in the three-dimensional space of the height,width and length of the flow channel,and under different conditions.The main aggregation locations are inconsistent;the smaller the flow rate,the larger the gas phase distribution and the higher the flow rate is which can effectively slow down the distribution of the gas phase;the larger the bubble diameter and the higher the rotation speed,the more serious the gas phase distribution.(3)As the gas volume fraction increases,the internal velocity streamline of the impeller and the volute becomes more disordered,and the vortex distribution increases.The larger the bubble diameter,the more the vortex.With the increase of the rotational speed,the most turbulent position of the gas streamline and vortex offset in the direction of increasing flow.(4)When the gas volume fraction is 5%,the gas phase aggregation is accelerated.When the gas volume fraction reaches 10%,the phase separation phenomenon occurs in the impeller.When the gas volume fraction is 15%,the high-speed centrifugal pump will reach the flow-breaking state,achieving the extreme point of the gas content.(5)Under the same gas volume fraction,the farther the pump condition deviates from the design condition,the more severe the pressure fluctuation of each monitoring point in the tongue,the circumferential outlet and the impeller flow channel,and the more serious the imbalance of stability.The tongue is the main source of pulsation caused by pressure fluctuation.Its position is different,the pressure fluctuation value is different,and the main pulsation amplitude of each monitoring point occurs at the blade frequency and its multiplier,and the main pulsation frequency domain is in the low frequency region.The larger the bubble diameter,the larger the pulsation amplitude.As the gas volume fraction increases,the maximum pressure fluctuation amplitude at the tongue position gradually shifts toward the large bubble diameter.As the rotational speed increases,the pressure fluctuation gradually moves forward with the fluctuation of time in the same cycle.The vicinity of the gas content of 5% is the critical point that affects the speed of the high-speed centrifugal pump pressure fluctuation.(6)The smaller the inlet pressure,the more serious the internal cavitation of the impeller.When the inlet pressure is reduced to a certain value,the head will drop sharply.As the flow rate decreases,the corresponding steep drop point will be smaller,and the steep drop point will gradually move forward.The bubble volume fraction and velocity gradually increase,and the overall pressure value becomes smaller,and the fluctuation is more severe.The inlet pressure of around 0.5 atm is the boundary point that affects the bubble distribution,the pressure pulsation amplitude of the monitoring point,and the rate of increase of the radial force.The radial force is the largest when the degree of rotation is an integral multiple of 60°.