Numerical Prediction and Performance Experiment in a Deep-well Centrifugal Pump with Different Impeller Outlet Width

The existing research of the deep-well centrifugal pump mainly focuses on reduce the manufacturing cost and improve the pump performance, and how to combine above two aspects together is the most difficult and important topic. In this study, the performances of the deep-well centrifugal pump with four different impeller outlet widths are studied by the numerical, theoretical and experimental methods in this paper. Two stages deep-well centrifugal pump equipped with different impellers are simulated employing the commercial CFD software to solve the Navier-Stokes equations for three-dimensional incompressible steady flow. The sensitivity analyses of the grid size and turbulence model have been performed to improve numerical accuracy. The flow field distributions are acquired and compared under the design operating conditions, including the static pressure, turbulence kinetic energy and velocity. The prototype is manufactured and tested to certify the numerical predicted performance. The numerical results of pump performance are higher than the test results, but their change trends have an acceptable agreement with each other. The performance results indicted that the oversize impeller outlet width leads to poor pump performances and increasing shaft power. Changing the performance of deep-well centrifugal pump by alter impeller outlet width is practicable and convenient, which is worth popularizing in the engineering application. The proposed research enhances the theoretical basis of pump design to improve the performance and reduce the manufacturing cost of deep-well centrifugal pump.

EXPERIMENTAL STUDY ON HIGH-SPEED CENTRIFUGAL PUMPS WITH DIFFERENT IMPELLERS

The experimental study is carried out on high-speed centrifugal pumps withthree different impellers. The experimental results and analysis show that high-speed centrifugalpumps with a closed complex impeller can achieve the highest efficiency and the lowest headcoefficient followed by those with half-open impeller and open-impeller, and can obtain much easilystable head-capacity characrastic curve, while those with a half-open complex impeller can't. Thecharacteristic curve with a open impeller is almost constant horizontal line before droppingsharply. The results also show that the axial clearance between pump casing and impeller caninfluence greatly on the performance of centrifugal pumps.

Investigation of CFD Calculation Method of a Centrifugal Pump with Unshrouded Impeller

Currently, relatively large errors are found in numerical results in some low-specific-speed centrifugal pumps with unshrouded impeller because the effect of clearances and holes are not accurately modeled. Establishing an accurate analytical model to improve performance prediction accuracy is therefore necessary. In this paper, a three-dimensional numerical simulation is conducted to predict the performance of a low-specific-speed centrifugal pump, and the modeling, numerical scheme, and turbulent selection methods are discussed. The pump performance is tested in a model pump test bench, and flow rate, head, power and efficiency of the pump are obtained. The effect of taking into consideration the back-out vane passage, clearance, and balance holes is analyzed by comparing it with experimental results, and the performance prediction methods are validated by experiments. The analysis results show that the pump performance can be accurately predicted by the improved method. Ignoring the back-out vane passage in the calculation model of unshrouded impeller is found to generate better numerical results. Further, the calculation model with the clearances and balance holes can obviously enhance the numerical accuracy. The application of disconnect interface can reduce meshing difficulty but increase the calculation error at the off-design operating point at the same time. Compared with the standard k-ε, renormalization group k-ε, and Spalart-Allmars models, the Realizable k-ε model demonstrates the fastest convergent speed and the highest precision for the unshrouded impeller flow simulation. The proposed modeling and numerical simulation methods can improve the performance prediction accuracy of the low-specific-speed centrifugal pumps, and the modeling method is especially suitable for the centrifugal pump with unshrouded impeller.

Hydraulic Optimization of a Double-channel Pump's Impeller Based on Multi-objective Genetic Algorithm

Computational fluid dynamics（CFD） can give a lot of potentially very useful information for hydraulic optimization design of pumps, however, it cannot directly state what kind of modification should be made to improve such hydrodynamic performance. In this paper, a more convenient and effective approach is proposed by combined using of CFD, multi-objective genetic algorithm（MOGA） and artificial neural networks（ANN） for a double-channel pump＇s impeller, with maximum head and efficiency set as optimization objectives, four key geometrical parameters including inlet diameter, outlet diameter, exit width and midline wrap angle chosen as optimization parameters. Firstly, a multi-fidelity fitness assignment system in which fitness of impellers serving as training and comparison samples for ANN is evaluated by CFD, meanwhile fitness of impellers generated by MOGA is evaluated by ANN, is established and dramatically reduces the computational expense. Then, a modified MOGA optimization process, in which selection is performed independently in two sub-populations according to two optimization objectives, crossover and mutation is performed afterword in the merged population, is developed to ensure the global optimal solution to be found. Finally, Pareto optimal frontier is found after 500 steps of iterations, and two optimal design schemes are chosen according to the design requirements. The preliminary and optimal design schemes are compared, and the comparing results show that hydraulic performances of both pumps 1 and 2 are improved, with the head and efficiency of pump 1 increased by 5.7% and 5.2%, respectively in the design working conditions, meanwhile shaft power decreased in all working conditions, the head and efficiency of pump 2 increased by 11.7% and 5.9%, respectively while shaft power increased by 5.5%. Inner flow field analyses also show that the backflow phenomenon significantly diminishes at the entrance of the optimal impellers 1 and 2, both the area of vortex and intensity of vortex decreases in the whole flow channel. This paper provides a promising tool to solve the hydraulic optimization problem of pumps＇ impellers.

An improved large eddy simulation of two-phase flows in a pump impeller

An improved large eddy simulation using a dynamic second-order sub-grid-scale （SGS） stress model has been developed to model the governing equations of dense turbulent particle-liquid two-phase flows in a rotating coordinate system, and continuity is conserved by a mass-weighted method to solve the filtered governing equations. In the cur- rent second-order SGS model, the SGS stress is a function of both the resolved strain-rate and rotation-rate tensors, and the model parameters are obtained from the dimensional consistency and the invariants of the strain-rate and the rotation-rate tensors. In the numerical calculation, the finite volume method is used to discretize the governing equations with a staggered grid system. The SIMPLEC algorithm is applied for the solution of the discretized governing equations. Body- fitted coordinates are used to simulate the two-phase flows in complex geometries. Finally the second-order dynamic SGS model is successfully applied to simulate the dense turbu-lent particle-liquid two-phase flows in a centrifugal impeller. The predicted pressure and velocity distributions are in good agreement with experimental results.

Impact of Impeller Stagger Angles on Pressure Fluctuation for a Double-Suction Centrifugal Pump

Pressure fluctuation may cause high amplitude of vibration of double-suction centrifugal pumps, but the impact of impeller stagger angles is still not well understood. In this paper, pressure fluctuation experiments are carried out for five impeller configurations with different stagger angles by using the same test rig system. Results show that the stagger angles exert negligible effects on the characteristics of head and efficiency. The distributions of pressure fluctuations are relatively uniform along the suction chamber wall, and the maximum pressure fluctuation amplitude is reached near the suction inlet tongue region. The pressure fluctuation characteristics are affected largely by impeller rotation, whose dominant frequencies include impeller rotation frequency and its harmonic frequencies, and half blade passage frequency. The stagger angle exerts a small effect on the pressure fluctuations in the suction chamber while a great effect on the pressure fluctuation in volute casing, especially on the aspect of decreasing the amplitude on blade passage frequency. Among the tested cases, the distribution of pressure fluctuations in the volute becomes more uniform than the other impeller configurations and the level of pressure fluctuation may be reduced by up to 50% when the impeller stagger angle is close to 24° or 360°.The impeller structure pattern needs to be taken into consideration during the design period, and the halfway staggered impeller is strongly recommended.

3D Particle Image Velocimetry Test of Inner Flow in a Double Blade Pump Impeller

The double blade pump is widely used in sewage treatment industry,however,the research on the internal flow characteristics of the double blade pump with particle image velocimetry（PIV） technology is very little at present.To reveal inner flow characteristics in double blade pump impeller under off-design and design conditions,inner flows in a double blade pump impeller,whose specific speed is 111,are measured under the five off-design conditions and design condition by using 3D PIV test technology.In order to ensure the accuracy of the 3D PIV test,the external trigger synchronization system which makes use of fiber optic and equivalent calibration method are applied.The 3D PIV relative velocity synthesis procedure is compiled by using Visual C＋＋ 2005.Then absolute velocity distribution and relative velocity distribution in the double blade pump impeller are obtained.Test results show that vortex exists in each condition,but the location,size and velocity of vortex core are different.Average absolute velocity value of impeller outlet increases at first,then decreases,and then increases again with increase of flow rate.Again average relative velocity values under 0.4,0.8,and 1.2 design condition are higher than that under 1.0 design condition,while under 0.6 and 1.4 design condition it is lower.Under low flow rate conditions,radial vectors of absolute velocities at impeller outlet and blade inlet near the pump shaft decrease with increase of flow rate,while that of relative velocities at the suction side near the pump shaft decreases.Radial vectors of absolute velocities and relative velocities change slightly under the two large flow rate conditions.The research results can be applied to instruct the hydraulic optimization design of double blade pumps.

Concurrent implantation of intra-aortic balloon pumping with extracorporeal membrane oxygenation improved survival of patients with postcardiotomy cardiogenic shock

Background Extra-corporeal membranous oxygenation (ECMO)and intra-aortic balloon pumping (IABP) are widely used in patients with severe circulatory failure. The decision to initiate ECMO and IABP on optimal occasion in postcardiotomy cardiogenic shock (PCS) remains controversial in the absence of guidelines.

Role of Intra-Aortic Balloon Pump in Off-Pump Coronary Artery Bypass —A Vettath Modification

Objective: Hemodynamic deterioration during positioning of the heart has been the most critical complication of off-pump coronary artery bypass surgery. Pre-operative use of intra-aortic balloon pump has been shown to prevent this complication in high risk patients. The role of balloon pump in high risk patients has been questioned by our group. We modified the role of balloon pump in our patients, thus avoiding the conversion to cardiopulmonary bypass. Methods: 4063 off-pump coronary bypass surgeries were performed by a single surgeon in our center, over thirteen years. 130 intra-aortic balloons used between July 2002 and December 2015 were removed from the the-ater, once the distal anastomosis was performed. We studied this group of patients for—time and need for insertion, duration of balloon used, local insertion problems and survival. Results: Initially, we inserted intra-aortic balloons in high risk patients. We observed that, patients with low ejection fraction and patients with critical left main coronary artery disease were not the ones who actually needed balloon pump support. It was the patients who had ongoing ischemia, with preserved left ventricular function, and ST depression intra-operatively, who needed balloon pump support to perform complete anatomical revascularization. Conclusions: Intra-aortic balloon pump has helped us to position the heart without hemodynamic instability, thereby avoiding conversion to cardio-pulmonary bypass. This enabled us to perform off-pump surgery in virtually all areas of the heart, thus maintaining perfect hemodynamics.

EXPERIENCE WITH LEFT VENTRICULAR ASSIST IMPELLER PUMPS (Design and Construction)

Basic problems in the design and construction of impeller pumps were analysed with appropriate equations. Attention was focused on the reduction of the velocity variations. Newton shear, Renolds shear, velocity distributions, stream surfaces were discussed pertaining to axial, radial and mixed-flow impellers. Practical experience of the fabrication of impeller pumps based on the equations exposed was presented with illustrations. Advantages of such pumps are remarkable energy saving, obvious miniaturization and sensible reduction of hemolysis. Careful modifications were carried out on many points among them: impiller form, vane angle, stream surface polish, magnet-ferrofluid friction free seal, rotor concentricity and its rotational equilibrium, the pre-rotational swirl of blood flow at the pump inlet, all must be treated carefully following the theoretical require ments. The soundness of the design and the practical feasibility of the proposed equations have resulted in impeller pumps with encouraging preliminary results.

Casting process design and practice for coolant pump impeller in AP1000 nuclear power station

The coolant pump impeller casting is the only rotating component in the nuclear island of an AP1000 nuclear power station, and is required to have a 60-year service time, which requires advanced materials and processing technologies to guarantee. In this paper, the casting process was studied, designed and modified by means of numerical simulation. The gating system was distributed symmetrically and the runner diameter was a little bigger for avoiding sand wash and turbulence;the feeding system focused on the solution of blades feeding, as some parts of which should reach Severity Level 1 radioactive testing standard. Therefore, upper and lower plates cooperating with chillers acted as feeding method besides additional 2-3 times thickness;in addition, lowering sand core strength, decreasing pouring temperature and increasing dimension allowance would be adopted to avoid crack defects. Finally, the pilot impeller was cast. The results show that the casting process design is reasonable, as the liquid rises very smoothly when pouring, and no volume defects are found by means of 100% radioactive testing. Based on this casting process, 16 coolant pump impellers have been successfully produced and delivered to customers.

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.

Flow Properties of Turbulent Fiber Suspensions in a Stock Pump Impeller

A numerical method for predicting fiber orientation is presented to explore the flow properties of turbulent fiber suspension flowing through a stock pump impeller. The Fokker-Planck equation is used to describe the distribution of fiber orientation. The effect of flow-fiber coupling is considered by modifying the constitutive mode.The three-dimensional orientation distribution function is formulated and the corresponding equations are solved in terms of second-order and fourth-order orientation tensors. The evolution of fiber orientation, flow velocity and pressure, additional shear stress and normal stress difference are presented. The results show that the evolutions of fiber orientation are different along different streamlines. The velocity and its gradient are large in the concave wall region, while they are very small in the convex wall region. The additional shear stress and normal stress difference are large in the inlet and concave wall regions, and moderate in the mid-region, while they are almost zero in most downstream regions. The non-equilibrium fiber orientation distribution is dominant at the inlet and the concave wall regions. The flow will consume more energy to overcome the additional shearing losses due to fibers at the inlet and the concave wall regions. The change of flow rates has effect on the distribution of additional shear stress and normal stress difference. The flow structure in the inlet and concave wall regions is essential in the resultant rheological properties of the fiber suspension through the stock pump impeller, which will directly affect the flow efficiency of the fiber suspension through the impeller.

Effects on the renal artery blood flow during the intra-aortic balloonpumping was used

The effects of intra-aortic balloon pumping(IABP) on hemodynamic parameters inthe kidney were studied. The pulse produced by pumping activated the renal nervoussystem and reduced the renal vascular resistance. Therefore, the reduction of the renalvascular resistance is an important reason for the increase the renal blood flow duringintra-aortic balloon pumping.

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.

PREDICTION OF PUMP CHARACTERISTICS ACCORDING TO GEOMETRICAL PARAMETERS OF IMPELLER AND VOLUTE CASING

The geometrical parameters of impeller or volute casing (including guide vane ofmultistage pump) have a great effect on pump characteristics, but ultimately. the pump characteris-tics are determined by the geometrical parameters of impeller and volute casing cooperatively. Inthis essay the effect of impeller and volute casing on pump characteristics will be studiedquantitatvely from the angle cf optimal matching of them.

Flow excitation mechanisms of unbalanced impeller forces after pump power-trip of ultra-high head pump-turbines

To elucidate the dynamic mechanisms of unbalanced impellers in ultra-high head pump-turbines(PTs),this study employed a one-and three-dimensional coupled method to simulate the pump power-trip(PPT)process of an ultra-high head PT.The investigation revealed two novel pulsation frequency components,denoted as fDVand fINFT,associated with impeller forces.The pulsation intensities of these components were markedly higher than those of rotor-stator interaction frequency components in ultra-high head PTs.Notably,the fDVcomponents exhibited pulsations at 1–2 times the rated rotation frequency of the impeller,spanning the entire transition period.Meanwhile,the fINFTcomponents constituted a complex frequency band with various frequency values,primarily occurring near conditions(Q=0,n=0,M=0,and d M/dt=0).These two pulsation frequency components were predominantly linked to the unsteady evolution of dean vortices inside the volute and complex transitions of the flow pattern within the impeller,respectively.It is crucial to note that these unbalanced flow-induced impeller axial forces can elevate the risk of accidents where the rotor is subjected to significant upwind axial forces.These findings offer valuable insights into mitigating the risk of rotor lifting due to axial forces during PT events in ultra-high head PTs.

CFD simulation of single-phase flow in flotation cells:Effect of impeller blade shape,clearance,and Reynolds number

A series of numerical simulations of turbulent single-phase flows are performed to understand the flow and mixing characteristics in a laboratory scale flotation tank.Four impeller blade shapes covering a wide range of surface areas and lip lengths are considered to highlight and contrast the flow behavior predicted in the impeller stream.The mean flow close to the impeller is fully characterized by considering velocity components along the axial direction at different radial locations.Normalized results suggest the development of a comparatively stronger axial velocity component for a blade design with the smallest lip length,called big-tip impeller here.Normalized turbulent kinetic energy profiles close to the impeller reveal the existence of an asymmetric trailing vortex pair.The highest turbulence kinetic energy dissipation rates are observed close to the impeller blades and stator walls where the radial jet strikes the stator walls periodically.Furthermore,liquid phase mixing in the flotation cell is studied using transient scalar tracing simulations providing mixing time data.Finally,pumping capacity and efficiency of different impeller designs are calculated based on which the impeller blade design with a rectangular blade design is found to perform most efficiently.

Preoperative Intra-Aortic Balloon Counterpulsation in Coronary Artery Bypass Graft Patients with Severe Left Ventricular Dysfunction

Background: The intra-aortic balloon pumping (IABP) is the most used ventricular mechanical assist device. In recent years, the preoperative use in patients with severe ventricular dysfunction presents itself as a great benefic strategy to the postoperative recovery. This paper aim is to evaluate the IABP post-operative benefit in patients with severe ventricular dysfunction. Methods: From January 2011 to March 2016, 125 patients underwent a coronary artery bypass graft (CABG) with cardiopulmonary bypass and preoperative IABP in Teaching Hospital of the ABC Medical School and Hospital Estadual Mario Covas. The inclusion criteria were the presence of severe ischemic cardiomyopathy with left ventricular ejection fraction (LVEF) less than or equal to 40%, estimated by Doppler echocardiography using the Simpson method. The preoperative LVEF was 30.25% ± 8.53% and the diastolic diameter of the left ventricle (LVDD) 67.75 ± 16.37 mm. IABP was installed approximately 15 hours before the surgery. Results: The patients required the IABP for 2.4 ± 1.58 days, and vasoactive drugs, 4.8 ± 2.12 days. We performed 3.2 ± 1.9 grafts per patient and the total length of stay was 07 ± 5.52 days. Cardiopulmonary bypass time was 67 ± 10.95 minutes and anoxia time, 46.4 ± 10.06 minutes. Twelve patients (9.6%) had pneumonia and four (3.2%), atrial fibrillation. We observed a LVDD reduction to 63 ± 16.26 (p = 0.068) and LVEF enhancement to 36.50 ± 16.86 (p = 0.144). The data were analyzed statistically according to the Wilcoxon test. There were no deaths. Conclusion: The initial experience of the authors with the preoperative IABP in patients with severe left ventricular dysfunction suggests great benefit in post-operative recovery with im-provement of LVEF and reduction of LVDD.