Research on cooperative optimization of multiphase pump impeller and diffuser based on adaptive refined response surface method

Multiphase pumps play an important role in the exploitation of natural gas hydrate. Compared with ordinary pumps, they can handle fluids with higher gas volume fraction (GVF). Therefore, it is important to improve the performance of the pump under high GVF. A model pump is designed based on the design theory of axial flow pump and centrifugal pump inducer. The hydraulic performance of the model pump is verified by numerical simulation and experiment. The Sparse Grid method is applied to the design of experiment (DOE), and three different adaptive refined response surface methods (RSM) are applied to the build the approximate model. Refinement points and verification points are used to improve and verify the precision of the response surface, respectively. The model with high precision and high computational efficiency is obtained through comparison and analysis. The multi-objective optimization of the optimal response surface model is carried out by MOGA (Multi-Objective Genetic Algorithm) method. The pressure increment of the optimized model is increased by 38 kPa. The efficiency is significantly improved under large mass flow conditions. The hydraulic performance of the optimized model is compared with that of the basic model. And the reasons that affect the performance of the multiphase pump are analyzed.

A New Prediction Method for the Complete Characteristic Curves of Centrifugal Pumps

Complete pump characteristics (CPCs) are the key for establishing pump boundary conditions and simulating hydraulic transients. However, they are not normally available from manufacturers, making pump station design difficult to carry out. To solve this issue, a novel method considering the inherent operating characteristics of the centrifugal pump is therefore proposed to predict the CPCs. First, depending on the Euler equations and the velocity triangles at the pump impeller, a mathematical model describing the complete characteristics of a centrifugal pump is deduced. Then, based on multiple measured CPCs, the nonlinear functional relationship between the characteristic parameters of the characteristic operating points (COPs) and the specific speed is established. Finally, by combining the mathematical model with the nonlinear relationship, the CPCs for a given specific speed are successfully predicted. A case study shows that the predicted CPCs are basically consistent with the measured data, showing a high prediction accuracy. For a pump-failure water hammer, the simulated results using the predicted CPCs are close to that using the measured data with a small deviation. This method is easy to program and the prediction accuracy meets the requirements for hydraulic transient simulations, providing important data support for engineering design.

Performance optimization of liquid ring pumps based on Gappy POD surrogate model

To solve the problems of high calculation cost and difficult optimization caused by the complex gas–liquid two-phase flow in liquid ring pumps, an optimization method of a liquid ring pump impeller based on the proper orthogonal decomposition (POD) surrogate model was proposed. The impeller blade shape was parameterized by using the quartic Bezier curve. The sample was obtained from the uniform experimental design of blade shape design parameters. The POD surrogate model was constructed by the parameters of sample blade shape and its corresponding flow field data, which was used instead of CFD numerical simulation to predict the flow field variables under the perturbations of blade design parameters in the optimization process. And then, the gradient vector of the objective function to design variables was predicted quickly and accurately. The blade shape was updated continuously along the negative direction of the gradient vector, and then, the optimal design of the impeller was acquired. The calculation case results show that the relative error between the pressure field in the impeller predicted by the POD method and that of CFD simulation is less than 5%, and the calculation cost is only 1/8460 of CFD simulation. Compared with the original model, the flow field distribution in the optimized model is significantly improved, and the efficiency is promoted by 3.8%.

Investigation of the axial force on a varying-speed centrifugal pump impeller

Centrifugal impeller has high efficiency but obvious axial force problems because of the axial-to-radial flow direction change. It is easy to cause the over loading of thrust bearing and damage shaft system. Especially in varying-speed centrifugal pumps, the mechanism, characteristics, and influence of impeller axial force is complex. Therefore, experimental and numerical studies are conducted to resolve these problems in this case. The impeller axial force is comparatively investigated by analyzing zonal components, visualizing internal flow, and resolving pressure attenuation law in clearances. This study provides a new test scheme based on force sensors for measuring the impeller axial force. The results show that the variation tendency of impeller axial force is similar to that of pump head. Flow patterns show that streamline-rotation angle decreases with the increase of flow rate in clearances. As the key factor affecting impeller axial force, the static pressure distribution in the clearances can be divided into specific variation stages to specify the mechanism. Specially in this varying-speed case, the blade axial force shifts from positive to negative with the decrease of rotation speed from high to low. This study provides a good reference for solving the axial force problems for centrifugal pumps.

Analysis of Centroid Trajectory Characteristics of Axial-Flow Pump Impeller Under Hydraulic Excitation

The hydraulic excitation characteristics of axial flow pump unit are studied through theoretical analysis, numerical simulation and field test in this paper. The correlation between impeller hydraulic and radial vibration displacement of impeller centroid is obtained through theoretical analysis. Through the 1-way fluid-solid-interaction (FSI) numerical simulation, the distributions of water pressure and displacement on the impeller surface are obtained, and the time-domain and frequency-domain characteristics of transient hydraulic and radial displacement are revealed. Through the field test, the external characteristics of axial flow pump unit and the time-frequency characteristics of the pressure pulsation at the measuring points beside the inlet of the impeller are obtained. The comparisons between simulation results and experimental results show that the former is accurate and reliable.

Comparative Analysis of Strength and Modal Characteristics of a Full Tubular Pump and an Axial flow Pump Impellers Based on Fluid-Structure Interaction

Fluid-structure interaction (FSI) was used to determine the structural mechanical characteristics of full tubular and axial-flow pumps. The results showed that as the flow rate increases, the total deformation and equivalent stress are significantly reduced. The max total deformation (MTD) and the max equivalent stress (MES) of the full tubular pump impeller occur on the outer edge of the blade. There are two stress concentrations in the full tubular pump impeller, one of which is located in the outlet area of the rim, and the other is located in the outlet area of the hub. However, the MES of the axial-flow pump appears in the center of the blade hub. The performance difference between the full tubular pump and the axial-flow pump is mainly caused by the clearance backflow. The natural frequency of the full tubular pump is lower than that of the axial-flow pump on the basis of the modal results. The MES of the full tubular pump is mainly concentrated at the junction of the blade and the motor rotor, and the max thickness of the rim is 6mm, which can be more prone to cracks and seriously affect the safety and stability of the pump.