FEDSM2013-16598 NUMERICAL OPTIMAL DESIGN OF IMPELLER BACK PUMP-OUT VANES ON AXIAL THRUST IN CENTRIFUGAL PUMPS

ABSTRACT Axial thrust in centrifugal pu mps attracts extensive attention in order to improve the operating reliability of pu mps. High axial thrust can cause rapid thrust bearing wear and subsequent pump failure o r frequent overhauls. A centrifugal pump (XA65/20) was selected in this study, based on L 16 (4 3 ) orthogonal array and CFD methods. The time -averaged Navier-Stokes equation was calcu lated for a 3D steady flow in the model pump in ANSYS CFX with the standard k-ω turbulence model and standard wall function applied. The structured meshes with different numbers were used for comparison in order to confirm that the computational results were not influenced by the mesh. Meanwhile, the effects of impeller back pump -out vane geometrical parameters, including its thickness S k , its outlet diameter D e and axial clearance δ, on the axial thrust and performances of the model centrifugal pu mp were analy zed. The different orthogonal schemes were obtained on the different values of S k , D e , and δ. Finally, when the parameters of the impeller S k , D e , and δ are 5mm, 100mm, 1.5mm, respectively. The Best Efficiency Point (BEF) of 69.9% was achieved with 60.12m for the designed head and -952.133N for the minimu m total axial force. The corresponding impeller with minimu m total axial fo rce was considered as the optimal scheme and manufactured for experimental test. The external characteristics by CFD have a good agreement with their experimental data, wh ich also better verified the accuracy of the numerical method of axial thrust applied in this research. Back pump-out vane thickness Back pump-out vane outlet diameter Z Back pump-out vane number N (r/min) Rotating speed ρ (kg/m3) Density g (m/s2) Gravity acceleration H (m) Pressure head ω (rad/s) Angular speed p (Pa) Pressure INTRODUCTION One of the most challenging aspects in horizontal pumps design is represented by the accurate evaluation of the axial thrust acting on the rotating shaft. In order to balance axial thrust of centrifugal pu mps, many devices such as balancing disk, balancing dru m, balancing hole and sealing system are used In this paper, the model pu mp of XA65/20 was designed to study its axial thrust and external characteristics with S k , δ an

Numerical analysis of cavitating flow characteristics in impeller of residual heat removal pump

In order to investigate internal cavitating flow characteristics of the impeller in residual heat removal pumps, the three-dimensional cavitating flow in a residual heat removal model pump is numerically calculated by using the homogeneous mixture cavitation model based on the Rayleigh-Plesset equation and the shear stress transport SST k-ω turbulence model. The hydraulic performance curves, distributions of vapor volume fraction at NPSHA and the blade load profiles at the design flow rate are obtained. The numerical results show that the distribution of vapor volume fraction becomes non-axisymmetric with the decreasing of NPSHA, even some blade passages are blocked when NPSHA drops to 2.63 m. Vapor volume fraction distribution varies across blade span; the shorter the distance to the hub is, the higher the vapor fraction on the blade suction side is. Additionally, the cavity in the impeller shows a quasi-steady characteristic before the head starts to be deteriorated rapidly. Due to a sudden change in the primary flow direction near the eye of impeller, the blade load on the blade pressure side shows a sudden increasing and drop effect

Modeling of unsteady structure of sheet/cloud cavitation around a two-dimensional stationary hydrofoil

\u3cp\u3eCompared to non-cavitating flow, cavitating flow is much complex owing to the numerical difficulties caused by cavity generation and collapse. In the present work, cavitating flow around a two-dimensional Clark-Y hydrofoil is studied numerically with particular emphasis on understanding the cavitation structures and the shedding dynamics. A cavitation model, coupled with the mixture multi-phase approach, and the modified shear stress transport k-ω turbulence model has been developed and implemented in this study to calculate the pressure, velocity, and vapor volume fraction of the hydrofoil. The cavitation model has been implemented in ANSYS FLUENT platform. The hydrofoil has a fixed angle of attack of α = 8° with a Reynolds number of Re = 7.5 × 10\u3csup\u3e5\u3c/sup\u3e. Simulations have been carried out for various cavitation numbers ranging from non-cavitating flows to the cloud cavitation regime. In particular, we compared the lift and drag coefficients, the cavitation dynamics, and the time-averaged velocity with available experimental data. The comparisons between the numerical and experimental results show that the present numerical method is capable to predict the formation, breakup, shedding, and collapse of the sheet/cloud cavity. The periodical formation, shedding, and collapse of sheet/cloud cavity lead to substantial increase in turbulent velocity fluctuations in the cavitation regimes around the hydrofoil and in the wake flow.\u3c/p\u3

Numerical Analysis of Flow Phenomena in a Residual Heat Removal Pump

The hydraulic performances as well as the cavitation phenomena in a scaled residual heat removal pump were investigated by experimental and numerical methods, respectively. In particular, a 3D numerical model of cavitation was adopted to simulate the internal cavitating flow through the model pump. The hydraulic performances of the model pump predicted by numerical simulations were in good agreement with the corresponding experimental data. The main generation and evolution of attached cavitation throughout the blade channels at different cavitating conditions have been investigated using the vapor fraction ISO surface and in-plane velocity vectors. Results show that the low static pressure at the impeller inlet is the main reason for leading edge cavitation by correlation analysis of static pressure on the midspan of impeller. Cavitation proved to occur over a wide range of flow rates, producing a characteristic creeping shape of the head-drop curve and developing in the form of nonaxisymmetric cavities at design flow rate. Moreover, the occurrence of these cavities, attached to the suction surface of blades, was found to depend on the NPSHA value. Numerical and experimental results in this paper can provide better understanding of the origin of leading edge cavitation in residual heat removal pumps

Modeling of unsteady structure of sheet/cloud cavitation around a two-dimensional stationary hydrofoil

Compared to non-cavitating flow, cavitating flow is much complex owing to the numerical difficulties caused by cavity generation and collapse. In the present work, cavitating flow around a two-dimensional Clark-Y hydrofoil is studied numerically with particular emphasis on understanding the cavitation structures and the shedding dynamics. A cavitation model, coupled with the mixture multi-phase approach, and the modified shear stress transport k-ω turbulence model has been developed and implemented in this study to calculate the pressure, velocity, and vapor volume fraction of the hydrofoil. The cavitation model has been implemented in ANSYS FLUENT platform. The hydrofoil has a fixed angle of attack of α = 8° with a Reynolds number of Re = 7.5 × 105. Simulations have been carried out for various cavitation numbers ranging from non-cavitating flows to the cloud cavitation regime. In particular, we compared the lift and drag coefficients, the cavitation dynamics, and the time-averaged velocity with available experimental data. The comparisons between the numerical and experimental results show that the present numerical method is capable to predict the formation, breakup, shedding, and collapse of the sheet/cloud cavity. The periodical formation, shedding, and collapse of sheet/cloud cavity lead to substantial increase in turbulent velocity fluctuations in the cavitation regimes around the hydrofoil and in the wake flow

Assessment of improved Schnerr-Sauer model in cavitation simulation around a hydrofoil

To enhance the capability of Schnerr-Sauer model in simulating cavitating flows, in this study, we developed an improved Schnerr-Sauer model based on the Rayleigh-Plesset equation and homogeneous flow assumption. The model considers the effects of turbulent fluctuation and noncondensable gas. The unsteady cavitating flow over a two-dimensional Clark-Y hydrofoil was numerically investigated combined with the SST k-ω turbulence model, in which the turbulence eddy viscosity is corrected. We obtain the time-averaged lift and drag coefficients, the cavity shape evolution at cloud cavitation, and its x-velocity profiles from these calculations. Compared with available experimental data in the literature, the time-averaged lift and drag coefficients predicted from the improved Schnerr-Sauer model agree better with the experimental results than with those of the original. In addition, the modified model can accurately predict the characteristics of the time-averaged lift and drag coefficients during different cavitation conditions. Moreover, the improved model can better simulate the inception, growth, shedding, and collapse of cloud cavitation than the original model. The overall results prove the reliability and accuracy of the improved Schnerr-Sauer model in cavitating flow simulations over a hydrofoil

Performance-Enhancing Approaches for PEDOT:PSS-Si Hybrid Solar Cells

The emerging energy crisis has focused significant worldwide attention on solar cells. Although crystalline silicon solar cells are currently widely used, their high cost limits the development of solar power generation. Consequently, hybrid solar cells are becoming increasingly important, especially organic-Si hybrid solar cells (HSCs). Organic-Si HSCs combine a mature technology and high efficiency with the low-temperature manufacturing process and tunable optoelectronic properties of organic solar cells. The organic material can be P3HT, carbon nanotubes, graphene, and PEDOT:PSS. Here we review the performance of PEDOT:PSS/Si HSCs and methods for improving their efficiency, such as PEDOT:PSS modification, optimization of the trapping effect, passivation of the silicon surface, addition of an interface layer, improvement of a back contact, and optimization of the metal top electrode. This Review should help fill the gap in this area and provide perspectives for the future development of the PEDOT:PSS/Si HSCs

Real‐world comprehensive diagnosis and “Surgery + X” treatment strategy of early‐stage synchronous multiple primary lung cancer

Abstract Background Diagnosing and treating synchronous multiple primary lung cancers (sMPLC) are complex and challenging. This study aimed to report real‐world data on the comprehensive diagnosis and treatment of patients with early‐stage sMPLC. Materials and Methods A single‐center cohort study was carried out and a large number of patients with early‐stage sMPLC were included. A single‐ or two‐stage surgery was performed to remove the primary and co‐existing lesions. The “X” strategies, including ablation, SBRT, and EGFR‐TKIs treatment, were applied to treat the high‐risk residual lesions. Wide panel‐genomic sequencing was performed to assess the genetic heterogeneity of the co‐existing lesions. Results A total of 465 early‐stage sMPLC patients with 1198 resected lesions were included. Despite most patients being histologically different or harboring different genetic alternations, about 7.5% of the patients had the same histological type and driver gene mutation changes, comprehensive re‐evaluation is thus needed. The “Surgery + X” strategy showed remarkable efficacy and safety in treating multiple lesions. Follow‐up data revealed that the T2 stage (p = 0.014) and the solid presence of a primary lesion (p < 0.001) were significantly related to tumor recurrence. And a T2‐stage primary tumor had a significantly higher rate of developing new lesions after the initial surgery (p < 0.001). Conclusions In real‐world practice, histopathological and radiological evaluation combined with genetic analyses could be a robust diagnostic approach for sMPLC. The “Surgery + X” treatment strategy showed remarkable efficacy, superiority, and safety in the clinical treatment of early‐stage sMPLC