Changes In Flow Patterns Research Articles

CFD simulations of the transition between non-aerated and aerated conditions in uncovered unbaffled stirred tanks

The transition between non-aerated and aerated regimes in uncovered unbaffled stirred tanks (UUSTs) was investigated using computational fluid dynamics (CFD). The Volume of Fluid (VOF) method was employed to model the free surface dynamics under various operational conditions. The simulations were able to predict the peculiar experimentally observed behavior of UUSTs and revealed that at velocities below a critical threshold (N_<_Ncrit), the system remains non-aerated, while exceeding this threshold (N_≥_Ncrit) induces bubble ingestion, leading to significant changes in power consumption and flow patterns. The CFD simulations accurately predicted the behaviour of the Power Number (Np) as well as the vortex shape inside the tank both in subcritical and supercritical regimes and showed good agreement with original experimental data and correlations from the literature. Additionally, the modeling of the aerated regime successfully predicted the vortex shape, the bubble dispersion within the tank, and the cavities formed behind the blades.

Intracranial bypass for giant aneurysms treatment assessed by computational fluid dynamics (CFD) analysis

Unruptured giant intracranial aneurysms (GIA) are those with diameters of 25 mm or greater. As aneurysm size is correlated with rupture risk, GIA natural history is poor. Parent artery occlusion or trapping plus bypass revascularization should be considered to encourage intra-aneurysmal thrombosis when other treatment options are contraindicated. The mechanistic background of these methods is poorly studied. Thus, we assessed the potential of computational fluid dynamics (CFD) and fluid–structure interaction (FSI) analyses for clinical use in the preoperative stage. A CFD investigation in three patient-specific flexible models of whole arterial brain circulation was performed. A C6 ICA segment GIA model was created based on CT angiography. Two models were then constructed that simulated a virtual bypass in combination with proximal GIA occlusion, but with differing middle cerebral artery (MCA) recipient vessels for the anastomosis. FSI and CFD investigations were performed in three models to assess changes in flow pattern and haemodynamic parameters alternations (wall shear stress (WSS), oscillatory shear index (OSI), maximal time averaged WSS (TAWSS), and pressure). General flow splitting across the entire domain was affected by virtual bypass procedures, and any deficiency was partially compensated by a specific configuration of the circle of Willis. Following the implementation of bypass procedures, a reduction in haemodynamic parameters was observed within the aneurysm in both cases under analysis. In the case of the temporal MCA branch bypass, the decreases in the studied parameters were slightly greater than in the frontal MCA branch bypass. The reduction in the magnitude of the chosen area-averaged parameters (averaged over the aneurysm wall surface) was as follows: WSS 35.7%, OSI 19.0%, TAWSS 94.7%, and pressure 24.2%. FSI CFD investigation based on patient-specific anatomy models with subsequent stimulation of virtual proximal aneurysm occlusion in conjunction with bypass showed that this method creates a pro-thrombotic favourable environment whilst reducing intra-aneurysmal pressure leading to shrinking. MCA branch recipient selection for optimum haemodynamic conditions should be evaluated individually in the preoperative stage.

Brinkman–Bénard convection in a box with temperature modulation

A bounded porous box saturated with Newtonian fluid and subjected to a sinusoidal temperature gradient has various practical applications, such as solar energy storage, groundwater remediation, food processing, and chemical reactors. We address the generalization of the classical Rayleigh–Bénard convection problem in a horizontal fluid layer in an infinitely large domain heated from below to a finite three-dimensional box. We also look into a more intricate form of the modulated Rayleigh–Bénard problem in which the temperature at the bottom boundary varies sinusoidally. The Rayleigh number quantifies the non-sinusoidal part of the temperature gradient, while the amplitude and frequency of modulation describe the sinusoidal one. The critical Rayleigh number is determined using linear and nonlinear stability analyses; for the latter, the energy method is used. There is a possibility of subcritical instabilities, as evidenced by the energy stability estimates being lower than the linear ones. Furthermore, eigenvalues are obtained as a function of aspect ratios, modulation amplitude, and frequency for varying Darcy numbers. Modulation amplitude more significantly triggers a change in flow patterns at the onset of convection compared to the effect of other parameters. Considering water-saturated porous media made up of different materials, we report the critical temperature difference between lower and upper surfaces required for the onset of convection. In addition, a comparison between such a temperature difference obtained from linear theory and the energy method is also provided in the same manner. It is observed that subharmonic instability occurs for all considered porous media packed densely or sparsely.

Numerical model of changes in current patterns due to reclamation around the Mireng River estuary, Gresik

Abstract The Mireng River is in Gresik Regency and empties into the Madura Strait. Around the mouth of the Mireng River, two industrial areas require construction facilities through reclamation. The consequences of reclamation will cause phenomena due to the interaction of marine and environmental dynamics, which can change current patterns, wave heights, and sedimentation processes, affecting the surrounding environment. This study explicitly discusses the changes in flow patterns that occur due to reclamation. The investigation was performed using numerical model simulations with Delft 3D software. The model results show the movement pattern and current speed during the highest and lowest low tides. There was a change in the average flow speed to 0.18 m/s around the reclamation area due to flow obstruction due to reclamation. This condition has the potential for sedimentation to occur in the area. Therefore, mitigation efforts are needed to reduce this impact.

Does the upstream gate control scheme threaten the safety of extra-long pressurized water diversion tunnel: Gas–liquid evolution characteristics of the filling process

With the promotion of China's “National Water Networks” strategy, extra-long pressurized water diversion tunnels are increasingly implemented in trans-regional and trans-basin water diversion projects. Existing projects commonly employ middle or downstream gate control schemes, but setting the control gate at the upstream offers a new approach to mitigate the adverse effects of flow pattern changes and hydraulic inertia caused by gate operations. However, there is no precedent for a 200 km-extra-long pressurized water diversion tunnel worldwide, it is not clear whether deviating from established norms will create new problems, and how to illustrate the hydraulic evolution characteristics under this scheme is the primary challenge. Therefore, this study takes a follow-up project for China's South-to-North Water Diversion Project as the research object: (1) Modeling: establish a mathematical model of an extra-long pressurized water diversion tunnel based on the movement of gas–liquid interface; and (2) Simulating: analyze the transient process of two arrangement schemes (single-slope and variable-slope) under various operating conditions. The study reveals the characteristics of pressure distribution, flow rates, and water level variations along the tunnel, conducting a comparative analysis of different arrangement schemes. The findings demonstrate that, even under the most unfavorable assumption, the key indicators during the water filling process remain within the acceptable range specified by engineering design. Therefore, the adoption of the upstream gate control scheme for the extra-long water diversion tunnel is considered feasible. This research provides specific theoretical basis and technical support for the construction and operation of water diversion projects.

A modified capacitance tomography image reconstruction approach based on iterative shrinkage-thresholding algorithm combined with deep networks

Abstract Due to the ‘soft-field’ effect and the challenges posed by ill-posed and ill-conditioned inverse problems, it is difficult to obtain high quality images from an electrical capacitance tomography (ECT) system. To achieve both high-quality images and fast imaging speed with limited measurement data, an image reconstruction algorithm, which was initially proposed for compressive sensing, is adapted for ECT image reconstruction to optimize the ill-posed nature of its inverse problem. The proposed algorithm leverages deep learning networks inspired by the iterative shrinkage-thresholding algorithm (ISTA), thereby creating a model that is both mathematically interpretable and endowed with trainable parameters. Building upon this foundation, the conventional Landweber iteration is integrated with the ISTA-Net to refine the optimization process for ECT image reconstruction. In order to propose an effective model adapting to the actual multiphase flow characteristics and complex flow pattern changes, the training and test process is driven by a comprehensive dataset generated from dynamic simulations, rather than artificial samples of multiphase distributions. This numerical methodology simulates the dynamic measurement process of a virtual ECT sensor by coupling the gas–liquid two-phase flow field and the ECT electrostatic field. The results of the testing phase indicate that the proposed algorithm outperforms traditional ECT image reconstruction methods. Compared with the linear back projection algorithm, the average image error and gas fraction error have been reduced by 20.44% and 16.74%, respectively, while maintaining a computational speed comparable to that of the Landweber iteration. The accuracy of the new algorithm in reconstructing the two-phase interface and estimating the gas fraction has been validated by static experimental tests, showing its potential for practical application in online gas–liquid two-phase flow measurement scenarios.

The prognostic value of changes in pulmonary vein flow patterns after surgical repair for primary mitral regurgitation

Background: The pulmonary vein (PV) flow pattern is influenced by the presence of mitral regurgitation (MR). After a successful reduction in MR severity, the pattern is expected to be changed. We aimed to evaluate the prognostic value of a change in the PV flow pattern in patients with primary MR undergoing mitral valve repair (MVR). Methods: The PV flow pattern was assessed with transthoracic echocardiography in 216 patients (age 65 [IQR 56–72] years, 70% male) with primary MR before and after surgical MVR. The population was divided according to a change in the PV flow pattern following MVR into ‘improvers’ and ‘non-improvers’. Results: Non-improvers (15%) had a higher prevalence of paroxysmal AF at baseline (46% vs. 22%, p = 0.004), left ventricular dysfunction (LVEF ≤60%) (39% vs. 21%, p = 0.020), and had lower systolic pulmonary artery pressure (28[IQR 25–38] vs. 35[IQR 26–48] mmHg, p = 0.018) compared to improvers (85%). After a median follow-up of 83[IQR 43–140] months, 26(12%) patients died. Non-improvers had higher mortality rates than improvers (p = 0.009). On multivariable Cox regression analysis, a lack of improvement in the PV flow pattern remained independently associated with all-cause mortality (HR 2.322, 95% CI 1.140 to 4.729, P = 0.020). Conclusion: A lack of improvement in the PV flow pattern is independently associated with worse long-term survival in patients with primary MR undergoing MVR.

Modeling the settling and resuspension of microplastics in rivers: Effect of particle properties and flow conditions

Microplastics have numerous different shapes, affecting the fate and transport of these particles in the environment. However, theoretical models generally assume microplastics to be spherical. This study aims to develop a modeling approach that incorporates the shapes of microplastics to investigate the vertical transport of microplastics in rivers and simulate the effect of particle and flow characteristics on settling and resuspension. To achieve these aims, a mechanistic model was developed utilizing the mass-balance and hydrodynamic equations. Scenario analysis was implemented assigning different values to model parameters, such as bed shear stress, shape factor and particle size to simulate the effect of flow patterns and particle properties. The model outcomes revealed that the residence time of microplastics in the water column was longest in medium bed shear stress, whilst it was shortest in low bed shear stress. This suggests that the influence of turbulence is not unidirectional; it can both increase and decrease microplastic concentrations and residence time in the water column. According to the scenario analysis, the settling flux of microplastics was the highest for near-spherical particles and increased with the size of the particles, as well as with increasing bed shear stress. However, the resuspension of particles was primarily influenced by increasing bed shear stress, but the ranking of resuspension flux values for different shaped and sized microplastics exhibited alterations with changing flow patterns. Turbulent conditions predominantly influenced the resuspension of near-spheres and large microplastics. On the contrary, the settling of fibers and small microplastics were significantly influenced by changing flow patterns, whereas near-spheres and largest particles were least affected. The model results were sensitive to changes in shape factor developed for this model, therefore this parameter should be improved in future studies.

Research Progress on Influencing Factors of Erosion Corrosion in Oil Pipelines

Original sentence: &amp;quot;Erosion corrosion is a significant factor contributing to the thinning and failure of oil pipelines. This paper addresses the issue of erosion corrosion of oil pipelines in oil fields under the action of multiphase flow, the main factors affecting the erosion corrosion are introduced, including the hydrodynamic factors, solid particle properties, fluid medium properties and temperature, It summarizes and analyzes the mechanisms through which these different factors affect the erosion corrosion of oil pipelines. The paper points out that increased fluid velocity in oil pipelines, sudden changes in flow patterns, and turbulent kinetic energy can accelerate erosion corrosion to some extent, With the increase of flow rate, erosion corrosion mechanism will change from electrochemical corrosion dominant to erosion accelerated corrosion, There is a maximum value for erosion corrosion based on the solid particle impact angle. The harder and sharper the solid particles are, the stronger their impact on the pipeline, especially the impact of low Angle impact is more significant; however, the diameter and quantity of particles can affect the development of erosion corrosion due to &amp;apos;particle size effect&amp;apos; and &amp;apos;shielding effect.&amp;apos; Additionally, lower pH values and higher temperatures of the fluid medium will increase pipeline erosion corrosion. Finally, future research directions for studying erosion corrosion in oilfield pipelines under multiphase flow conditions are discussed in light of existing research.&amp;quot;

Research on multi-velocity measurement method of solid particles based on interdigital electrostatic sensor

Abstract In gas-solid two-phase flow, the velocities of solid particles will show different distributions as the flow pattern changes, and it is a challenging task to achieve the measurement of different velocity parameters in the flow field. To obtain the velocity information of solid particles in the flow field, a novel method to achieve multi-velocity measurement of solid particles is proposed by using the spatial filtering characteristics of interdigital electrostatic sensor with variational mode decomposition (VMD). Firstly, a three-dimensional model of the interdigital electrostatic sensor is established using COMSOL simulation software. Based on its spatial dynamic sensitivity, a theoretical analysis of its spatial filtering characteristics is conducted to obtain a mathematical relationship for velocity measurement. Subsequently, the VMD decomposition method is applied to an experiment involving charged wires, with the experimental results verifying the effectiveness of VMD in achieving multi-scale decomposition of electrostatic signals. Finally, the proposed measurement method is validated on a gravity feeding device and a pneumatic conveying system. The experimental results demonstrate that the method exhibits good feasibility.

Review: Flow Diversion for the Treatment of Middle Cerebral Artery Aneurysms.

The invention of flow diverting stents (FDS) is a novel milestone in the field of endovascular aneurysm therapy, promoting physiological healing of the vessel segment contrary to prior deconstructive treatment strategies, such as coiling. The effects of FDS are based on changes in flow patterns, segmental wall stabilization, and the growth of a neointima. Although flow diversion is already well established for cerebral aneurysms in proximal segments, peripheral locations remain challenging. Especially the middle cerebral artery (MCA) with its predominance of non-collateralized perforators and functional end arteries that supply the eloquent areas of the brain is of major concern.The literature was reviewed for flow diversion of the MCA and antiplatelet therapy.Resulting from the special anatomical characteristics of the MCA, FDS implantation in this territory is completely different from the proximal vessel segments. Still, flow diversion represents an effective endovascular strategy, especially in otherwise non-accessible or sufficiently treatable lesions. However, the risk of ischemic adverse events might be increased. Special attention to the individual decision regarding device selection, antiplatelet regimen, and exact definition of the proximal and distal landing zone considering the jailed side branches is essential for a good angiographic and clinical outcome. · MCA aneurysms can be sufficiently treated by FDS.. · The anatomic and hemodynamic characteristics of the MCA result in an increased risk of thromboembolism.. · Individual device selection and antiplatelet regimen are essential for treatment success.. · Schüngel M, Wohlgemuth WA, Elolf E et al. Review: Flow Diversion for the Treatment of Middle Cerebral Artery Aneurysms. Fortschr Röntgenstr 2024; DOI 10.1055/a-2343-0046.

Comparison of Maximum Heat Transfer Rate of Thin Vapor Chambers with Different Wicks under Multiple Heat Sources and Sinks

In this paper, we present a new analytical model to investigate the maximum heat transfer rate of a thin vapor chamber (TVC) with multiple heat sources and sinks. The model can specifically consider different heat flux conditions for each heat source. Both capillary limitations and allowable maximum temperature constraints were employed to determine the maximum heat transfer rate. The liquid and vapor pressure distributions within the TVC were analytically derived using the Brinkman-extended Darcy equation and the Hagen–Poiseuille equation, respectively. Additionally, the theoretical wall temperature distribution was calculated based on the 3D energy equation, considering different heat flux conditions for multiple heat sources with a weighting factor. Our results demonstrate that the heat flux conditions applied to the heat sources significantly impact the internal flow pattern of the TVC. These changes in flow patterns influence the pressure distributions of the liquid and vapor, thereby affecting the maximum heat transfer rate. Furthermore, the effects of wick parameters on the maximum heat transfer rate under various heat flux conditions were examined.

Identification of Traffic Flow Spatio-Temporal Patterns and Their Associated Weather Factors: A Case Study in the Terminal Airspace of Hong Kong

In this paper, a data-driven framework aimed at investigating how weather factors affect the spatio-temporal patterns of air traffic flow in the terminal maneuvering area (TMA) is presented. The framework mainly consists of three core modules, namely, trajectory structure characterization, flow pattern recognition, and association rule mining. To fully characterize trajectory structure, abnormal trajectories and typical operations are sequentially extracted based on a deep autoencoder network with two specially designed loss functions. Then, using these extracted elements as basic components to further construct and cluster per-hour-level descriptions of airspace structure, the spatio-temporal patterns of air traffic flow can be recognized. Finally, the association rule mining technique is applied to find sets of weather factors that often appear together with each flow pattern. Experimental analysis is demonstrated on two months of arrival flight trajectories at Hong Kong International Airport (HKIA). The results clearly show that the proposed framework effectively captures spatial anomalies, fine-grained trajectory structures, and representative flow patterns. More importantly, it also reveals that those flow patterns with non-conforming behaviors result from complex interactions of various weather factors. The findings provide valuable insights into the causal relationships between weather factors and changes in flow patterns, greatly enhancing the situational awareness of TMA.

Predicting impaired cerebrovascular reactivity and risk of hyperperfusion syndrome in carotid artery stenosis using BeamSAT magnetic resonance imaging

Pencil-beam presaturation (BeamSAT) magnetic resonance imaging (MRI) produces selective magnetic resonance angiography (MRA) images of specific arteries, including the unilateral internal carotid artery (ICA-selective MRA) or vertebral artery (VA-selective MRA). We evaluate the influence of flow pattern, visualized using BeamSAT MRI, on preoperative cerebral hemodynamic status and postoperative hyperperfusion syndrome (HPS). Patients undergoing carotid artery stenting or carotid endarterectomy were categorized into two groups to evaluate flow pattern. Patients with neither crossflow on BeamSAT MRI nor mismatch in middle cerebral artery (MCA) signal intensity between ICA-selective and conventional MRA were classified into Group I, comprising 29 patients. Group II included all other patients comprising 19 patients, who were suspected of experiencing changes in intracranial flow patterns. Cerebral blood flow and cerebrovascular reactivity (CVR) were assessed using single-photon emission computed tomography, and potential HPS symptoms were retrospectively assessed by chart review. Preoperative ipsilateral CVR was significantly lower in Group II than in Group I (18.0% ± 20.0% vs. 48.3% ± 19.5%; P < 0.0001). Group II showed significantly impaired CVR (odds ratio 17.7, 95% confidence interval 1.82–171; P = 0.013) in multivariate analysis. The partial areas under the curve of the BeamSAT logistic model (0.843) were significantly larger than those of the conventional logistic model (0.626) over the range of high sensitivity (0.6–1) (P = 0.04). The incidence of postoperative HPS symptoms was significantly higher in Group II than in Group I (8/19 vs. 1/29; P = 0.001). BeamSAT MRI may be a valuable and non-invasive tool for assessing cerebral hemodynamics and predicting postoperative HPS.

Development of microstructure-rheological and electrical properties relationship in PS/POE/HNTs blend nanocomposites using machine learning

Halloysite nanotubes (HNTs) and polypropylene-grafted maleic anhydride (PP-g-MA) were studied for their effects in blends of polystyrene (PS) and polyolefin elastomer (POE). The method used to prepare PS/POE blends (90/10 and 80/20 wt/wt) containing 1, 3, and 5 phr HNTs with or without PP-g-MA (a compatibilizer) was melt blending. Structural and morphological studies using X-ray diffraction analysis (XRD), scanning electron microscopy assisted energy dispersive X-ray spectroscopy (SEM-EDS), and transmission electron microscopy (TEM) confirmed a matrix-droplet morphology and the sample containing compatibilizer has better microstructure than the other formulations. The presence of both PP-g-MA and HNTs together has been discovered to improve the viscoelastic properties of the solid, as evidenced by increased storage modulus and complex viscosity. A notable change occurred in the rheological behavior of the PS/POE blends containing 5 phr of PP-g-MA and HNTs. The dependence of zero-shear viscosity on HNTs loading (0–5 phr) was approximated as a polynomial curve by fitting the experimental data with the Carreau-Yasuda model. Computational fluid dynamics (CFD) simulations were also used to study the effects of HNTs loading on changes in fluid flow patterns and shear rates. The calculated effective viscosities at a given shear rate (0.05 1/s) were in qualitative agreement with the experimental results. Moreover, we utilized various machine-learning techniques to predict the complex viscosity of PS/POE blends and their nanocomposites. The results showed that Extreme Gradient Boosting (XGBoost) outperformed other predictive models based on evaluation metrics. Four-point probe measurements found that the samples containing 5 phr HNT had the lowest conductivities due to the presence of aggregated structures. However, the homogeneous distribution of HNT led to a sudden rise in conductivity in the samples containing 5 phr of PP-g-MA. Computer modeling results of samples with uniform and non-uniform HNT distributions showed that the conductivity decreased with HNT loading and decreased considerably compared to the uniform distribution.

Required volume for color flow injection test to confirm the intravascular placement of a peripheral venous catheter

Background: Confirmation of adequate peripheral intravenous catheter placement is essential before using venous catheters. The color flow injection test has been reported as a method with high sensitivity and specificity for this purpose. The technique involves administrating saline through the peripheral venous route to observe changes in the color flow pattern around the same vein at a more central location. However, the required volume of saline remains uncertain. This study aims to determine the appropriate dosage for conducting the test in pediatric patients and explore any potential correlations between dosage and patient characteristics. Methods: A prospective study was conducted in children under 6 years of age with American Society of Anesthesiologists Physical Status 1–2 presenting for general anesthesia. After an intravenous cannula was placed in the forearm under general anesthesia, normal saline was injected at a speed of approximately 1 mL/s while the axillary artery and vein were observed with color flow Doppler imaging. The volume of normal saline required to induce a change in the color flow pattern around the vessels was measured. Measurements were performed twice and averaged for comparison with patient characteristics and other factors. Results: The study cohort included 30 patients aged from 0.3 to 5.5 (2.6 ± 1.6) years. The change in color flow Doppler imaging was noted in all the patients, and the average volume was 1.40 ± 0.36 mL (95% confidence interval (CI), 1.27–1.54; p &lt; 0.001), which was significantly correlated with age, with a correlation coefficient of 0.435 (95% CI, 0.09–0.69; p = 0.02). Conclusions: The required volume for the color flow injection test is small; therefore, the test is easy to perform and minimally invasive in pediatric patients.

Preparative Fractionation of Brazilian Red Propolis Extract Using Step-Gradient Counter-Current Chromatography.

Propolis is a resinous bee product with a very complex composition, which is dependent upon the plant sources that bees visit. Due to the promising antimicrobial activities of red Brazilian propolis, it is paramount to identify the compounds responsible for it, which, in most of the cases, are not commercially available. The aim of this study was to develop a quick and clean preparative-scale methodology for preparing fractions of red propolis directly from a complex crude ethanol extract by combining the extractive capacity of counter-current chromatography (CCC) with preparative HPLC. The CCC method development included step gradient elution for the removal of waxes (which can bind to and block HPLC columns), sample injection in a single solvent to improve stationary phase stability, and a change in the mobile phase flow pattern, resulting in the loading of 2.5 g of the Brazilian red propolis crude extract on a 912.5 mL Midi CCC column. Three compounds were subsequently isolated from the concentrated fractions by preparative HPLC and identified by NMR and high-resolution MS: red pigment, retusapurpurin A; the isoflavan 3(R)-7-O-methylvestitol; and the prenylated benzophenone isomers xanthochymol/isoxanthochymol. These compounds are markers of red propolis that contribute to its therapeutic properties, and the amount isolated allows for further biological activities testing and for their use as chromatographic standards.

The Change of Flow Pattern from Stratified to Stratified-Wavy for Condensation in Wire on Tube Heat Exchangers

Flow patterns inside wire-on-tube condensers with different refrigerant mass flow rates were studied in a theoretical study. In this study, tubes with diameters of 3.25 mm (3/16"), 4.83 mm (1/4") and 6.29 mm (5/16") were used. R-134a and R-600a cooling fluids were used at condensing temperatures of 54.4°C, 45°C, and 35°C. The results of this study were obtained using Equal Equation Solver (EES) software. The proposed model was able to predict the type of refrigerant flow pattern based on the limitations reported in previous studies. It was possible to distinguish four kinds of flow patterns: laminar, wavy laminar, plugged, and spiral. The first variation in flow pattern from laminar to wavy laminar flow found between 0.8 and 0.39, and a second variation in flow pattern found from wavy laminar flow to plug or slug flow between 0.15 and 0.05. For the refrigerant conditions, the condensation temperature did not affect the flow pattern. When using R-134a, the inner tube diameter had no effect on the flow pattern. Change occurs with R-600a as inner diameter was increased.

Investigation on large fluctuation transient process of high head Pelton turbine

Abstract With the development of hydropower in southern western China, the Pelton turbine is the only choice in this ultra-high head condition which is nearly 1000 m. However, the complex coupling structure of the internal and external flow of the Pelton turbine, the change of flow pattern during the transition process, and the fluid-solid interaction of the bucket greatly increases the difficulty of accurate numerical simulation. Therefore, there are relatively few studies and applications on the transition process of the Pelton turbine. In this paper, the theoretical analysis, numerical calculation on the internal complex flow and the external characteristics of the turbine during the large fluctuation transition process are carried out in three aspects. First, the internal flow mechanism under optimized conditions is investigated, such as Dean vortex pairs, secondary flow, etc. And then analyze the influence of the flow state distribution on the jet flow. Secondly, study the instability and flow characteristics in the large fluctuation transition process of the opening and closing process of the nozzle, and predict the mechanism of the jet flow and the impact on the bucket during the dynamic process. Finally, study change of the hydraulic characteristics under the dynamic process which provides a theoretical guarantee for the safe operation of the Pelton turbine.

Study of the Effect of Incoming Flow with Fluctuating Gas Void Fraction on Transient Characteristics of a Three-stage Multiphase Pump

Abstract For the oil field with high gas content, the oil well produced has obvious gas content fluctuation characteristics. The unsteady flow of multiphase pump will be caused by the fluctuation flow into the pump. In this paper, the unsteady numerical simulation of the flow field in a three-stage multiphase pump is carried out by using Euler-Euler two-fluid model and SST turbulence model. The results show that the pressurization and torque of each impeller change with the fluctuation of the inlet gas content. The second stage impeller has the highest fluctuation due to the change of flow pattern. The inlet gas rate pulsation frequency and static and static interference have significant effects on the pressure pulsation in the impeller, and the dominant frequency is gas rate pulsation frequency or 11 times rotation frequency. The dominant frequency of the diffuser is the blade passing frequency and its double frequency, and the pulsation frequency of the gas content is the secondary frequency and the amplitude is relatively stable. The axial force increases with the increase of gas content, while the radial force changes in reverse.