MULTIOBJECT OPTIMIZATION OF A CENTRIFUGAL IMPELLER USING EVOLUTIONARY ALGORITHMS

Application of the multiobjective evolutionary algorithms to the aerodynamicoptimization design of a centrifugal impeller is presented. The aerodynamic performance of acentrifugal impeller is evaluated by using the three-dimensional Navier-Stokes solutions. Thetypical centrifugal impeller is redesigned for maximization of the pressure rise and blade load andminimization of the rotational total pressure loss at the given flow conditions. The Bezier curvesare used to parameterize the three-dimensional impeller blade shape. The present method obtains manyreasonable Pareto optimal designs that outperform the original centrifugal impeller. Detailedobservation of the certain Pareto optimal design demonstrates the feasibility of the presentmultiobjective optimization method tool for turbomachinery design.

Robust Design Optimization Method for Centrifugal Impellers under Surface Roughness Uncertainties Due to Blade Fouling

Blade fouling has been proved to be a great threat to compressor performance in operating stage. The current researches on fouling-induced performance degradations of centrifugal compressors are based mainly on simplified roughness models without taking into account the realistic factors such as spatial non-uniformity and randomness of the fouling-induced surface roughness. Moreover, little attention has been paid to the robust design optimization of centrifugal compressor impellers with considerations of blade fouling. In this paper, a multi-objective robust design optimization method is developed for centrifugal impellers under surface roughness uncertainties due to blade fouling. A three-dimensional surface roughness map is proposed to describe the nonuniformity and randomness of realistic fouling accumulations on blades. To lower computational cost in robust design optimization, the support vector regression（SVR） metamodel is combined with the Monte Carlo simulation（MCS） method to conduct the uncertainty analysis of fouled impeller performance. The analyzed results show that the critical fouled region associated with impeller performance degradations lies at the leading edge of blade tip. The SVR metamodel has been proved to be an efficient and accurate means in the detection of impeller performance variations caused by roughness uncertainties. After design optimization, the robust optimal design is found to be more efficient and less sensitive to fouling uncertainties while maintaining good impeller performance in the clean condition. This research proposes a systematic design optimization method for centrifugal compressors with considerations of blade fouling, providing a practical guidance to the design of advanced centrifugal compressors.

Inverse Method of Centrifugal Pump Impeller Based on Proper Orthogonal Decomposition (POD) Method

To improve the accuracy and reduce the calcu- lation cost for the inverse problem of centrifugal pump impeller, the new inverse method based on proper orthog- onal decomposition （POD） is proposed. The pump blade shape is parameterized by quartic Bezier curve, and the initial snapshots is generated by introducing the perturbation of the blade shape control parameters. The internal flow field and its hydraulic performance is predicted by CFD method. The snapshots vector includes the blade shape parameter and the distribution of blade load. The POD basis for the snap- shots set are deduced by proper orthogonal decomposition. The sample vector set is expressed in terms of the linear combination of the orthogonal basis. The objective blade shape corresponding to the objective distribution of blade load is obtained by least square fit. The Iterative correction algorithm for the centrifugal pump blade inverse method based on POD is proposed. The objective blade load dis- tributions are corrected according to the difference of the CFD result and the POD result. The two dimensional and three dimensional blade calculation cases show that the proposed centrifugal pump blade inverse method based on POD have good convergence and high accuracy, and thecalculation cost is greatly reduced. After two iterations, the deviation of the blade load and the pump hydraulic perfor- mance are limited within 4.0% and 6.0% individually for most of the flow rate range. This paper provides a promising inverse method for centrifugal pump impeller, which will benefit the hydraulic optimization of centrifugal pump.

An automated approach to calculating the maximum diameters of multiple cutters and their paths for sectional milling of centrifugal impellers on a 4_(1/2)-axis CNC machine

Power generators and chemical engineering compressors include heavy and large centrifugal impellers. To produce these impellers in high-speed machining, a 4?-axis milling machine(or a 4-axis machine plus an indexing table) is often used in the industry, which is more rigid than a5-axis milling machine. Since impeller blades are designed with complex B-spline surfaces and impeller channels spaces vary significantly, it is more efficient to use multiple cutters as large as possible to cut a channel in sections and a blade surface in patches, instead of only using a small cutter to machine a whole blade and a channel. Unfortunately, no approach has been established to automatically calculate the largest diameters of cutters and their paths, which include the indexing table angles. To address this problem, an automated and optimization approach is proposed. Based on the structure of a 4?-axis machine, a geometric model for a cutter gouging/interfering the impeller is formulated, and an optimization model of the cutter diameter in terms of the indexing table angle is established at a cutter contact(CC) point on a blade surface. Then, the diameters of the tools,their orientations, and the indexing table angles are optimized, and each tool's paths are generated for machining its corresponding impeller section. As a test, an impeller is efficiently machined with these tools section by section; thus, this approach is valid. It can be directly used in the industry to improve efficiency of machining centrifugal impellers.

LES Analysis of the Unsteady Flow Characteristics of a Centrifugal Pump Impeller

Stall phenomena increase the complexity of the internal flow in centrifugal pump impellers.In order to tackle this problem,in the present work,a large eddy simulation(LES)approach is applied to determine the characteristics of these unstable flows.Moreover,a vorticity identification method is used to characterize quantitatively the vortex position inside the impeller and its influencing area.By comparing the outcomes of the numerical simulations and experimental results provided by a Particle Image Velocimetry(PIV)technique,it is shown that an apparent“alternating stall”phenomenon exists inside the impeller when relatively small flow rate conditions are considered.The stall is generated near the suction side of the blade inlet,grows towards the high-pressure side of the blade in the circumferential direction,and gradually attenuates.As the flow rate decreases,the number of stalls remains unchanged,while the related influencing area and strength gradually increase and the circumferential velocity increases.

CONSTRUCTION DESIGN AND FLOW ANALYSIS OF CENTRIFUGAL PUMP IMPELLER WITH SUPER-LOW SPECIFIC SPEED

Some commonly used constructions and their design principles of centrifugal pump impeller with super low specific speed are introduced. The internal flow related to pump performance is analysed primarily.

COMPARISON OF TWO METHODS TO INCREASE TIP CLEARANCE AND ITS EFFECT ON PERFORMANCE OF TURBOCHARGER CENTRIFUGAL COMPRESSOR STAGE

Tip clearance between the blade tip and casing of a centrifugal compressor can be varied through two methods： by changing the blade height （MI） or by changing the casing diameter （M2）. Numerical simulations are carried out to compare these two methods and their effect on the stage and impeller performance. The impeller and diffuser are connected through rotor stator boundary using frozen rotor approach. Overall stage performance and the flow configuration have been investigated for nine tip clearance levels from no gap to 1 mm. Impeller and diffuser performances are also presented separately. It has been found that the overall and impeller performance are comparatively better for MI below tip clearance of 0.5 mm whereas M2 is found advantageous above 0.5 mm of tip clearance. Both MI and M2 show performance degradation with the increase in tip clearance. Two models have been proposed for the stage total pressure ratio and efficiency, which are found to be in agreement with experimental results. The impeller efficiency and the pressure ratio are found to be maximum at tip clearance of 0.1 mm for both the cases however minimum diffuser effectiveness is also observed at the same clearance level. Diffuser effectiveness is found to be maximum at zero gap for both cases. As it is practically impossible to have zero gap for unshrouded impellers so it is concluded that the optimum thickness is 0.5 mm onwards for MI and 0.5 mm for M2 in terms of diffuser effectiveness. Mass averaged flow parameters, entropy, blade loading diagram and relative pressure fields are presented, showing the loss production within the impeller passage with tip clearance.

Investigation of rotating stall for a centrifugal pump impeller using various SGS models

The accurate modeling and prediction of the rotating stall in a centrifugal pump is a significant challenge. One of the modeling techniques that can improve the accuracy of the flow predictions is the large eddy simulation （LES）. The quality of the LES predictions depends on the sub-grid-scale （SGS） model implemented in the LES. This paper assesses the influence of various SGS models that are suitable for predicting rotating stall in a low-specific speed centrifugal pump impeller. The SGS models considered in the present work include the Smagorinsky model （SM）, the dynamic Smagorinsky model （DSM）, the dynamic non-linear model （DNM）, the dynamic mixed model （DMM） and the dynamic mixed non-linear model （DMNM）. The results obtained from these models are compared with the PIV and LDV experimental data. The analysis of the results shows that the SGS models have significant influences on the flow field. Among the models, the DSM, the DMM and the DMNM can successfully predict the ＂two-channel＂ stall phenomenon, but not the SM and the DNM. According to the simulations, the DMNM gives the best prediction on the mean velocity flow field and also indicates improvements for the simulation of the turbulent flow. Moreover, the high turbulent kinetic energy predicted by the DMNM is in the best agreement with the experiment data.

Adsorption Performance of Sliding Wall-Climbing Robot

Sliding wall-climbing robot （SWCR） is applied worldwide for its continuous motion, however, considerable air leakage causes two problems： great power consumption and big noise, and they constraint the robot＇s comprehensive performance. So far, effective theoretical model is still lacked to solve the problems. The concept of SWCR＇s adsorption performance is presented, and the techniques of improving utilization rate of given adsorption force and utilization rate of power are studied respectively to improve SWCR＇s adsorption performance. The effect of locomotion mechanism selection and seal＇s pressure allocation upon utilization rate of given adsorption force is discussed, and the theoretical way for relevant parameters optimization are provided. The directions for improving utilization rate of power are pointed out based on the detail analysis results of suction system＇s thermodynamics and hydrodynamics. On this condition, a design method for SWCR-specific impeller is presented, which shows how the impeller＇s key parameters impact its aerodynamic performance with the aid of computational fluid dynamics （CFD） simulations. The robot prototype, BIT Climber, is developed, and its functions such as mobility, adaptability on wall surface, payload, obstacle ability and wall surface inspection are tested. Through the experiments for the adhesion performance of the robot adsorption system on the normal wall surface, at the impeller＇s rated rotating speed, the total adsorption force can reach 237.2 N, the average effective negative pressure is 3.02 kPa and the design error is 3.8% only, which indicates a high efficiency. Furthermore, it is found that the robot suction system＇s static pressure efficiency reaches 84% and utilization rate of adsorption force 81% by the experiment. This thermodynamics model and SWCR-specific impeller design method can effectively improve SWCR＇s adsorption performance and expand this robot applicability on the various walls. A sliding wall-climbing robot with high adhesion efficiency is developed, and this robot has the features of light body in weight, small size in structure and good capability in payload.

非设计工况下带分流叶片半开式离心叶轮内部流动特性数值研究

In order to investigate the complex flow characteristics inside an unshrouded centrifugal impeller with splitter blades at off-design conditions,and analyze its influence on pump operation stability,a numerical simulation study was carried on using the curvature-corrected SST-CC turbulence model;the head and efficiency accorded with experimental results.The pressure fluctuation,unsteady radial force and velocity were analyzed quantitatively and the numerical results indicate this:the peak to peak value of pressure fluctuation in the impeller channel gradually increases in the flow direction and at 0.49Qn,the slope of peak to peak value to normalized impeller channel behind the splitter blade is 8.57 times greater than that before the splitter blade.The greater the flow rate deviates from the design condition,the larger the peak to peak value of the pressure fluctuation and radial force;in particular at 0.27Qn,the maximum radial force is 194.29%greater than that of the design condition.When the operating flow rate is smaller than 0.83Qn,the stall occurs and the stall vortex could block the impeller discharge;as the flow rate decreases further,the pressure amplitude at rotational frequency gradually increases in the impeller channel and the prevailing frequency changes from the blade passage frequency(BPF)to the rotating stall frequency in the diffuser.The tip leakage vortex(TLV)is generated in the tip region and rotated move downstream in the impeller flow channel,and the backflows appear on the blade suction side and in the tip and the tongue regions;the smaller the flow rate,the more serious the TLV and backflow phenomenon.The rotating stall causes uneven flow in the impeller channel,increasing the pressure fluctuation and the radial force,and resulting in an imbalance of the impeller rotation.

Damage mechanism and evaluation model of compressor impeller remanufacturing blanks:A review

The theoretical and technological achievements in the damage mechanism and evaluation model obtained through the national basic research program“Key Fundamental Scientific Problems on Mechanical Equipment Remanufacturing”are reviewed in this work.Large centrifugal compressor impeller blanks were used as the study object.The materials of the blanks were FV520B and KMN.The mechanism and evaluation model of ultra-high cycle fatigue,erosion wear,and corrosion damage were studied via theoretical calculation,finite element simulation,and experimentation.For ultra-high cycle fatigue damage,the characteristics of ultra-high cycle fatigue of the impeller material were clarified,and prediction models of ultra-high cycle fatigue strength were established.A residual life evaluation technique based on the“b-HV-N”(where b was the nonlinear parameter,HV was the Vickers hardness,and N was the fatigue life)double criterion method was proposed.For erosion wear,the flow field of gas-solid two-phase flow inside the impeller was simulated,and the erosion wear law was clarified.Two models for erosion rate and erosion depth calculation were established.For corrosion damage,the electrochemical and stress corrosion behaviors of the impeller material and welded joints in H2S/CO2 environment were investigated.KISCC(critical stress intensity factor)and da/dt(crack growth rate,where a is the total crack length and t is time)varied with H2S concentration and temperature,and their variation laws were revealed.Through this research,the key scientific problems of the damage behavior and mechanism of remanufacturing objects in the multi-strength field and cross-scale were solved.The findings provide theoretical and evaluation model support for the analysis and evaluation of large centrifugal compressor impellers before remanufacturing.