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Investigation on the stall types in impellers with different blade numbers

Journal of Hydrodynamics 2023年第2期35卷 299-313页

作者： Xiao-dong Liu Yao-jun Li Zhu-qing Liu Wei Yang College of Water Resources and Civil Engineering China Agricultural UniversityBeijing100083China Beijing Engineering Research Center of Safety and Energy Saving Technology for Water Supply Network System China Agricultural UniversityBeijing100083China

Stall is a complex flow phenomenon and its existence usually shows significant differences in different impeller forms.In this paper,the flow field characteristics and mechanism of stall types in impellers with different blade numbers were studied through the combination of experiment and numerical simulation at stall inception stage.In the experiments,it was observed that the five-blade impeller entered the rotating stall stage from a relatively stable flow field within a small flow rate interval.For the six-blade impeller,the root cause that stall vortices appeared in channels alternately rather than each one evenly was also reasonably explained.The validated numerical simulation method was utilized to reveal the three-dimensional flow field in impeller channels.The results indicate the swirling vortex near the impeller shroud was periodically sucked in and escaped from region near the blade suction side,which was the fundamental driving force of rotating stall.The sudden change of flow field caused by the fusion of the separation vortex at the channel inlet and the vortex induced by the swirling vortex near shroud is the essential reason for the formation of alternating stall.What’s more,the stall inception flow field is clearly defined in impellers,which is of great significance for the further analysis of stall characteristics.Based on the distribution characteristics of vortex structure near impeller shroud with different blade numbers at different flow rate conditions,this paper deeply investigated the formation mechanism of different stall types in impellers.

关键词： Numerical simulation high-frequency particle image velocimetry(PIV) impellers swirling vortex stall type

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Experimental investigation of characteristics of instability evolution in a centrifugal compressor

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Chinese Journal of Aeronautics 2023年第4期36卷 174-189页

作者： Hanzhi ZHANG Ce YANG Ben ZHAO Wei ZHAO Chenxing HU Wenli WANG Jianbing GAO Shijun SUN School of Mechanical Engineering Beijing Institute of TechnologyBeijing 100081China Institute of Engineering Thermophysics Chinese Academy of SciencesBeijing 100190China School of Aerospace Engineering Beijing Institute of TechnologyBeijing 100081China

The stable range of operation for the centrifugal compressor significantly influences the dynamic,economic,and environment-friendly characteristics of power systems.A deep understand-ing of the characteristics of instability evolution is necessary to improve the compressor stability.A centrifugal compressor equipped with a vaneless diffuser is experimentally investigated using high-response static-pressure measurements.The results obtained indicate that three typical rotational-speed ranges exist based on the different instability evolution characteristics,which reveals the var-ious impeller–diffuser matching behaviors over the entire speed range.At low-speed ranges((40%–75%)N_(max),N_(max)is the maximum rotational speed),the compressor exhibits stable,Rotating Insta-bility(RI),impeller stall(diffuser stall),and surge modes.The impeller stall mode is induced by RI and propagates downstream,resulting in the diffuser stall and compressor surge modes.In the medium-speed range((75%–85%)N_(max)),the compressor exhibits stable,diffuser stall,RI,and surge modes.In the high-speed range((85%–100%)N_(max)),the compressor exhibits stable,diffuser stall,and surge modes.The dominant instability position is shifted from the impeller to the diffuser as the rotational speed increases.Both the impeller and diffuser stall present an irregular sawtooth static-pressure wave and exhibit broadband frequency spectrum patterns.

关键词： Centrifugal compressor impellers Pressure measurement Rotating instability Stability Stall

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Micromixing of a Two Phase System in a Stirred Tank with Multiple impellers

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Advances in Materials Physics and Chemistry 2012年第4期2卷 150-153页

作者： Lei Yang Jingcai Cheng Ping Fan Chao Yang Key Laboratory of Green Process and Engineering Institute of Process Engineering Chinese Academy of Sciences Beijing 100190 China

The competitive iodide/iodate reaction scheme was used to ascertain the micromixing in the stirred solid-liquid systems. Two different glass beads from 450 to 1250 μm were tested. The effect of solid particles on reaction selectivity with multiple impellers at different feed points has been investigated. It was confirmed that glass beads as a second phase were suitable for the study. The segregation index has changed significantly only for the medium-sized particles at relatively high solid holdups. The cloud formation was clearly observed for the medium-sized particles at a concentration of 12.12 wt. %. When feeding into the clear liquid above the cloud, the value of the segregation index increased significantly. However, in the presence of particles of 1-1.25 mm, the influence on the selectivity was negligible when the agitation speed was increased.

关键词： Micromixing Parallel Reactions Two Phases Multiple impellers

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Tool Path Generation for Clean-up Machining of Impeller by Point-searching Based Method

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Chinese Journal of Aeronautics 2012年第1期25卷 131-136页

作者： TANG Ming ZHANG Dinghua LUO Ming WU Baohai The Key Laboratory of Contemporary Design and Integrated Manufacturing Technology Ministry of EducationNorthwestern Polytechnieal UniversityXi'an 710072China

Machining quality of clean-up region has a strong influence on the performances of the impeller. In order to plan clean-up tool paths rapidly and obtain good finish surface quality, an efficient and robust tool path generation method is presented, which employs an approach based on point-searching. The clean-up machining mentioned in this paper is pencil-cut and multilayer fillet-cut for a free-form model with a ball-end cutter. For pencil-cut, the cutter center position can be determined via judging whether it satisfies the distance requirement. After the searching direction and the tracing direction have been determined, by employing the point-searching algorithm with the idea of dichotomy, all the cutter contact （CC） points and cutter location （CL） points can be found and the clean-up boundaries can also be defined rapidly. Then the tool path is generated. Based on the main concept of pencil-cut, a multilayer fillet-cut method is proposed, which utilizes a ball-end cutter with its radius less than the design radius of clean-up region. Using a sequence of intermediate virtual cutters to divide the clean-up region into several layers and given a cusp-height tolerance for the final layer, then the tool paths for all layers are calculated. Finally, computer implementation is also presented in this paper, and the result shows that the proposed method is feasible.

关键词： NC machining impellers tool path clean-up point-searching

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Dynamic Characteristic Analysis and Experiment for Integral Impeller Based on Cyclic Symmetry Analysis Method

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Chinese Journal of Aeronautics 2012年第5期25卷 804-810页

作者： WU Qiong ZHANG Yidu ZHANG Hongwei State Key Laboratory of Virtual Reality Technology and Systems School of Mechanical Engineering and AutomationBeihang UniversityBeijing 100191China

A cyclic symmetry analysis method is proposed for analyzing the dynamic characteristic problems of thin walled integral im- peller. Reliability and feasibility of the present method are investigated by means of simulation and experiment. The fundamental cyclic symmetry equations and the solutions of these equations are derived for the cyclic symmetry structure. The computational efficiency analysis between whole and part is performed. Comparison of results obtained by the finite element analysis （FEA） and experiment shows that the local dynamic characteristic of integral impeller has consistency with the single cyclic symmetry blade. When the integral impeller is constrained and the thin walled blade becomes a concerned object in analysis, the dynamic characteristic of integral impeller can be replaced by the cyclic symmetry blade approximately. Hence, a cyclic symmetry analy- sis method is effectively used to improve efficiency and obtain more information of parameters for dynamic characteristic of integral impellers.

关键词： dynamic characteristic cyclic symmetry impellers simulation finite element analysis blade

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PERIODIC BOUNDARY CONDITION IN SIMULATION OF TURBULENT FLOW

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Journal of Hydrodynamics 2002年第3期14卷 111-116页

作者： Zhou, Xiao-Quan Cao, Shu-You Qu, Lun-Fu Wu, Yu-Lin Hydraulics Lab. of High Speed Flows Sichuan Univ. Chengdu 610065 China Dept. of Thermal Eng. Tsinghua Univ. Beijing 100084 China

The simulations of the three-dimensional turbulent flows through hydraulic turbine components[1] were conducted based on the standard k-Ε turbulent model with body-fitted coordinates and staggering grid system. The SIMPLEC algorithm was adopted in the numerical procedure. A new method to treat the periodic boundary condition was used. The calculated results of the new method were compared with those of traditional ones. These results indicate that the new method can give much better results, and can be used in simulating flow through rotational impellers. The presented method can be combined with alternative turbulent model or employed in large eddy simulation.

关键词： Computer simulation Hydraulic turbines impellers Three dimensional Time varying systems

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Numerical Simulation of Optimization of Mixing Tank for Residue Upgrading Reactor

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China Petroleum Processing & Petrochemical Technology 2019年第2期21卷 110-117页

作者： Bao Di Tang Xiaojin Zhu Zhenxing SINOPEC Research Institute of Petroleum Processing

For studying the mixing tank for RMAC (residue upgrading to maximize asphaltene conversion) reactor, the CFD simulation was employed to simulate the flow field in the mixing tank. The dispersion of liquid-liquid phase in the mixing tank and the power of turbines were investigated. The simulation results showed that compared with the original doublelayer propeller, the A310-swept double-layer impellers could reduce the liquid heterogeneous degree by 27.5% and the stirring power by 3.25%. The influence of rotation speed on the heterogeneous degree and stirring power was investigated, and the critical rotation speed was obtained. The optimal rotation speed was determined to be 240 r/min. The heterogeneous degree was 0.19 and the minimum stirring power was 10.89 W. By optimizing the impeller selection and process conditions, the overall performance of the mixing tank could be significantly improved.

关键词： liquid-liquid mixing impellers numerical simulation critical rotation speed

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Radiotracer Investigation of the Effect of Impeller Type on Mixing in Industrial Process Simulator

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Journal of Applied Mathematics and Physics 2018年第3期6卷 468-474页

作者： Simon Yao Adzaklo Christian Priesley Kofi Dagadu Ishmael Iddisah Mumuni Patience Adwoa Serwah Adu Hannah Asamoah Affum Godfred Kofi Appiah Alexander Coleman National Nuclear Research Institute Ghana Atomic Energy Commission Legon-Accra Ghana

Radiotracer technology has been applied in industry for the investigation of process performance, online monitoring of conditions of process units, troubleshooting and diagnosing anomalies including mixing conditions in continuous stirred tank reactors. In this study, radiotracer methodology was used to carry out investigation on a laboratory water flow rig which serves as simulator of industrial processes. The aims of the investigation were to assess: i) the effect of impeller type on mixing and ii) the fluid dynamics of the water in the vessels since both the vessels and the impellers were redesigned and reconstructed. Four similar vessels in series circuit with different impeller configurations were investigated. Tank 1 has 1 axial impeller, Tank 2 has 2 axial impellers, Tank 3 has 2 radial impellers and Tank 4 has no impeller. The data were collected by introducing 8 mCi liquid technetium-99 m at the inlet stream of the vessels and the gamma signal was detected with thallium activated NaI detector placed at the outlet of the vessels. Residence Time Distribution (RTD) curves for the outlet tracer concentration were generated from which the Mean Residence Time (MRT) and the variance were calculated by the method of moments. The extent of material mixing in the vessels was inferred from the variances and the fluid dynamics was obtained by modeling. The extent of mixing was highest in Tank 2 followed by Tank 3, and Tank 4 gave the poorest mixing. The outlet response curves were fitted with mathematical models using DTS pro and “RTD Software”. The best fit for Tanks 2, 3 and 4 was Perfect Mixers in Series with Exchange (PMSE) model while Perfect Mixers in Series with Recycle (PMSR) model best described the fluid dynamics of the material in Tank 1.

关键词： Axial impellers Mixing Radial Radiotracer

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