| Liquid ring pump is a kind of fluid machinery used to transport gas,which is widely used in electric power,chemical industry,coal mine,pharmaceutical and other important fields of national economy because of its advantages such as large flow rate,no metal surface contact and small temperature changes during compression.The complicated gas-liquid two-phase flow in the pump will result in high-level vibration and noise,low efficiency and blade fracture.The gas-liquid two-phase flow in the pump is so complicated that the performance optimization of the pump is difficult to achieve,which makes it difficult to meet the vital demands in nuclear power,petrochemical,coal mine safety and other fields.To overcome these problems,the 2BEA liquid ring pump was taken as the research object.The complicated gas-liquid two-phase flow characteristics in the pump were analyzed by numerical and experimental approaches.The gas-liquid two-phase flow structure and transient characteristics of the flow in the pump were experimentally studied.The eigen-decomposition and prediction analysis of transient gas-liquid two-phase flow field in the impeller of liquid ring pump based on the proper orthogonal decomposition(POD)reduced-order model were carried out,and the hydraulic performance optimization of liquid ring pump was implemented based on POD surrogate model.The main work and research results are as follows:1.The visualization of gas-liquid two-phase flow structure in the liquid ring pump and the experimental test of hydraulic excitation characteristics were carried out.The results show that the number of bubbles immersed in the liquid-ring increases gradually with the increase of rotating speed.The shape of the gas-liquid free interface and the distribution of wake vortex and channel vortex in the liquid-ring were obtained by using the tracer application of bubbles on the flow characteristic in liquid-ring.The pressure pulsation in the pump is unevenly distributed in the circumferential direction of the casing.The main source of pressure pulsation is the periodic evolution of complex wake vortex structure.In addition,the flow separation and rotor-stator interaction also have a great influence to the pressure fluctuation on the inner wall of the casing.The dominant frequency of the bearing house vibration is caused by mechanical resonance,and the main characteristic frequency of the casing vibration is related to the hydraulic excitation in the pump.The base vibration is greatly affected by the vibration conduction excitation of the bearing house.2.Based on the high-precision numerical results of LES model for the gas-liquid two-phase flow field in the liquid ring pump,the transient characteristics of gas-liquid flow in the pump were analyzed.The complex vortex structure in liquid ring pump was identified by using vortex identification technology.The results show that the low frequency signal ofpressure fluctuation in the pump casing is related to the periodic development and evolution of low-frequency vortex.The pressure pulsation of the impeller outlet has obvious partitioning features along the circumferential direction.The rotor-stator interaction has little effect on the unsteady characteristics of the upstream flow at the pump inlet,but it has a greater impact on the unsteady characteristics of the downstream flow at the pump outlet.There are complex low-frequency counter-flow vortices in the exhaust diffuser.With the rotation of the impeller,the channel vortex on the suction side gradually flows out of the impeller passage,which collides with the impeller exit wake vortex and the separation vortex developed on the inner wall of the casing,and finally forming a more complex flow structure.The wake vortex on the exhaust side and the separation vortices on the inner wall of the casing flow into the impeller passage together under the high-speed rotation of the impeller.Q-criterion and ?-criterion have the same ability to identify the three-dimensional vortex structure in the pump,but the ?-criterion is capable to analyze the vortex structures with different intensities and scales simultaneously in gas-liquid two-phase flow.3.The axial clearance leakage flow structures of the liquid ring pump impeller and its interference on the hydraulic performance and main flow field characteristics of the pump were analyzed.The results show that the axial clearance leakage of the liquid ring pump mainly occurs in the compression region and the suction region.The leakage flow and the main flow mix together to form the gap leakage vortex.The clearance leakage has a certain impact on the hydraulic performance of the pump,and has little interference on the main characteristics of the flow field in the pump.The axial mainstream gas in the suction section of the liquid ring pump has a certain interference on the leakage flow of the axial clearance at the suction side.The flow rate of liquid ring pump is more sensitive to the leakage of the axial clearance,and the leakage of the axial clearance of impeller is more serious under the condition of small flow rate.4.The eigen-decomposition and prediction analysis of transient gas-liquid two-phase flow field in the impeller of liquid ring pump based on the POD reduced-order model were carried out.The results show that the POD method can realize the spatio-temporal decoupling analysis of gas-liquid transient flow field in liquid ring pump.The variation of modal coefficients of flow field in time domain can reflect the law of energy,frequency and phase of modal field.The modes with different energy can characterize the flow field structure with different characteristics and scales,and several modes with higher energy can basically contain most of the flow field information.The gas-liquid flow filed in the sample space can be accurately predicted by the POD reduced-order model,and the maximum relative errors of the predicted results for inlet pressure of pump,phase field and velocity field in impeller areabout 0.2%,4% and 8%,respectively.The POD reduced-order model has a certain extrapolation accuracy.However,the prediction accuracy of POD reduced-order model gradually decreases when the object is gradually far away from the sample space.5.The performance optimization of liquid ring pump based on POD surrogate model was implemented.The POD surrogate model was constructed from the blade profile parameters of the initial samples and the corresponding flow field parameters,which was used to replace the CFD numerical simulation to predict the flow field perturbation response with the perturbation of blade profile control parameters quickly and accurately.The gradient vector of the objective function to the control variable was predicted,and the blade profile was optimized along the gradient vector direction.The optimization results of the example show that the relative error between the predicted results of POD method and that of CFD is less than 5%,and the amount of calculation is significantly reduced.Compared with the original model,the efficiency of the optimized model is improved by 3.8%.Therefore,POD surrogate model can greatly reduce the calculation cost of flow field simulation in hydraulic performance optimization of liquid ring pump. |
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