Study on the internal flow characteristics and hydraulic excitation forces of the hydrogenation feed pump

Francis turbines are widely used due to their large capacity and broad head adaptability, placing higher demands on the internal flow characteristics and runner performance of the units. In this paper, numerical simulations of a Francis turbine model were conducted using ANSYS CFX 2022 R1. The SST turbulence model, ZGB cavitation model, and VOF multiphase flow model were selected for the calculations. The internal flow characteristics and pressure pulsations in the runner and draft tube under different operating conditions were analyzed, and the variations in normal and tangential forces acting on the runner blades during operation were investigated. The results indicate significant differences in the internal flow within the runner and draft tube under various guide vane opening conditions. The pressure pulsation in the unit is influenced by both the internal flow in the draft tube and the rotation of the runner. The mechanical load on the runner blades is affected by multiple factors, including the wake from upstream fixed guide vanes, rotor–stator interaction, and downstream vortex ropes. Under low-flow conditions, the variation in forces acting on the runner blades is relatively small, whereas under high-flow conditions, the runner blades are prone to abrupt force fluctuations at 0.6–0.8 times the rotational frequency. This is manifested as periodic abrupt force changes in both the X and Y directions of the runner blades under high-flow conditions. The normal force in the Z-direction of the runner blades increases instantaneously and then decreases immediately, while the tangential force decreases instantaneously and then increases promptly.

With the growing global demand for renewable energy, the pump as turbine (PAT) exhibits significant potential in the micro-hydropower sector. To reveal its internal unsteady flow characteristics and energy loss mechanisms, this study analyzes the internal flow field of an ultra-low specific speed pump as turbine (USSPAT) by employing a combined approach of entropy generation theory and dynamic mode decomposition (DMD). The results indicate that the outlet pressure pulsation characteristics are highly dependent on the flow rate. Under low flow rate conditions, pulsations are dominated by low-frequency vortex bands induced by rotor-stator interaction (RSI), whereas at high flow rates, the blade passing frequency (BPF) becomes the absolute dominant frequency. Energy losses within the PAT are primarily composed of turbulent and wall dissipation, concentrated in the impeller and volute, particularly at the impeller inlet, outlet, and near the volute tongue. DMD reveals that the flow field is governed by a series of stable modes with near-zero growth rates, whose frequencies are the shaft frequency (25 Hz) and its harmonics (50 Hz, 75 Hz, 100 Hz). These low-frequency modes, driven by RSI, contain the majority of the fluctuation energy. Therefore, this study confirms that RSI between the impeller and the volute is the root cause of the dominant pressure pulsations and periodic energy losses. This provides crucial theoretical and data-driven guidance for the design optimization, efficient operation, and stability control of PAT.

The influence of eccentric needle movement on internal flow and injection characteristics of a multi-hole diesel nozzle

This study presents the numerical analysis on the inter-blade vortex characteristics along with the blockage effects of runner blade in a Francis hydro turbine model with various flow rate conditions. The turbine model showed different flow characteristics in the runner blade passages according to operating conditions, and inter-blade vortex was observed at lower flow rate conditions. This inter-blade vortex can lead to performance reduction, vibration, and instability for smooth operation of turbine systems. The previous study on blockage effects on various runner blade thickness, showed its influence on hydraulic performance and internal flow characteristics at low flow rate conditions. Therefore, the inter-blade vortex characteristics can be altered with the blockage effects at low flow rate conditions in a Francis hydro-turbine. For investigating the internal flow and unsteady pressure characteristics, three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes calculations are performed. These inter-blade vortices were captured at the leading and trailing edges close to the runner hub. These vortex regions showed flow separation and stagnation flow while blockage effects contributed for decreasing the inter-blade vortex at low flow rate conditions.

Unstable operation during the no-load startup of pumped storage hydroelectric power plants is a significant factor affecting the successful grid connection of units. To investigate the internal flow and pressure pulsation characteristics during the no-load startup of pump-turbine under varying heads, the vertical single-stage mixed-flow reversible pump-turbine is studied. Numerical simulations are performed using the SST k-ω turbulence model, and the Fast Fourier Transform (FFT) method is employed to analyze the pressure pulsation signals. A comparative study is conducted on the pressure pulsation characteristics and internal flow features at different positions under various heads. The results indicate that the pressure pulsation in the draft tube cone region is the most severe, with the dominant blade passing frequency (fBPF ) and its harmonics caused by rotor-stator interaction (RSI) in the spectra of pressure pulsations at various heads in the draft tube cone region. Additionally, the pressure pulsation amplitude increases as the head decreases, while low-frequency pulsation signals are prevalent throughout the entire flow passage. Compared to the flow condition, the influence of rotor-stator interaction on pressure pulsation is more significant. During the no-load startup at the highest head, the pump-turbine exhibits the most vortex structures and the poorest flow condition, while the intensity of pressure pulsation in the draft tube cone region is the lowest. These research findings provide a basis for the stable no-load startup of pump-turbine.

This paper establishes a model of flexible multibody dynamics for conrod small end bearing based on extended Reynolds equation considering lubricating oil fill ratio and average flow model. It analyzes internal flow process and characteristics of lubricating oil, discusses oil film formation and distribution mechanism, and acquires influence law of revolving speed and modeled lines on internal flow. Results show the flow of lubricating oil in conrod small end is mainly affected by relative motion of piston pin and bushing, and further spreads circumferentially, and inhales from outside and flows out axially; with revolving speed increases, average volume flow rate is higher, and minimum oil film thickness is reduced; neither the in-cylinder pressure nor change of bushing internal surface molded line affects average volume flow rate significantly.

Computational study of internal flow characteristics of the air induction nozzle

Internal flow characteristics within Y-jet atomizers and the local drop size distribution and cross-sectional averaged drop size at the outside were investigated with the liquid and air injection pressures, mixing port length of atomizers, and the liquid properties taken as parameters. To examine the effect of the liquid viscosity, glycerin-water mixtures were used in this study. The liquid viscosity plays only a minor role in determining the internal flow pattern and the spatial distribution shape of drops, but the drop sizes themselves generally increase with increasing of the liquid viscosity. An empirical correlation for the liquid discharge coefficient at the liquid port was deduced from the experimental results; the liquid discharge coefficient strongly depends on the liquid flow area at the mixing point which is proportional to the local volumetric quality(.betha.), and the volumetric quality was included in the correlation. Regardless of the value of the liquid viscosity, the compressible flow through the gas port was well represented by the polytropic expansion process(k=1.2), and the mixing point pressure could be simply correlated to the aspect ratio( / ) of the mixing port and the air/liquid mass flow rate ratio( / ) as reported in the previous study.udy.udy.y.

When a Pelton turbine operates in sand laden water, the abrasive wear of its overflow components by high-speed jets is serious. Based on the VOF (volume of fluid) multiphase flow model, the SST (shear stress transfer) k-ω turbulence model, the particle motion Lagrangian model, the generic wear model, and the SIMPLEC (Semi-Implicit Method for Pressure Linked Equations Consistent) algorithm, the liquid–air–solid three-phase flow in the key overflow components of a Pelton turbine were simulated, the abrasive wear was predicted, and the internal sand-water flow characteristics and the abrasive wear of the overflow components were analyzed. The results show that the trailing edge at the root of the runner bucket, the leading face of the bucket near the root, the notch, and the splitter are severely worn. The abrasive wear of the splitter and the notch is more severe than that of the leading face of the bucket. The wear rate from the splitter to the trailing edge increases first and then decreases. The wear pattern of the needle tip is mainly “dotted”, while that of the nozzle opening is “flaky”, and the abrasive wear of the nozzle opening is more severe than that of the needle. The predicted results are consistent with the actual conditions at the site of the power station. This study provides a technical method for the prediction of abrasive wear of the Pelton turbine and a technical basis for the operation and maintenance of the power station.

Undesirable flow phenomena in Francis turbines are caused by pressure fluctuations induced under conditions of low flow rate; the resulting vortex ropes with precession in the draft tube (DT) can degrade performance and increase the instability of turbine operations. To suppress these DT flow instabilities, flow deflectors, grooves, or other structures are often added to the DT into which air or water is injected. This preliminary study investigates the effects of anti-cavity fins on the suppression of vortex ropes in DTs without air injection. Unsteady-state Reynolds-averaged Navier–Stokes analyses were conducted using a scale-adaptive simulation shear stress transport turbulence model to observe the unsteady internal flow and pressure characteristics by applying anti-cavity fins in the DT of a Francis turbine model. A vortex rope with precession was observed in the DT under conditions of low flow rate, and the anti-cavity fins were confirmed to affect the mitigation of the vortex rope. Moreover, at the low flow rate conditions under which the vortex rope developed, the application of anti-cavity fins was confirmed to reduce the maximum unsteady pressure.

The development of the injector nozzle is a dynamic area in regard of several technical aspects. At first, the internal flow influences the near-field spray characteristics via various phenomena such as cavitation and turbulence. However, these phenomena are not fully understood due to their extremely fast, complex and multiscale nature. Furthermore, it governs the spray targeting inside the combustion chamber. High-speed X-ray imaging of GDI injector nozzles is performed in this study. The experimental results presented are related to the internal flow and primary breakup of discharged liquid jets. The injectors used are equipped with nozzles made of aluminum which have been specially developed for these investigations to enhance optical accessibility. The visualization of the needle motion, in-nozzle flow and the primary breakup region provides several exciting observations. First, the needle lift tracking exhibits short overshooting right before the steady-state of the injection phase. This event leads to a short-term, however, significant change in the associated performance of the breakup. This phenomenon is found to be a consequence of the transient behavior of the in-nozzle flow. It is shown that under some circumstances hydraulic flip may occur during this overshooting period. The primary jet breakup region is visualized and evaluated by means of image processing. Thus, the transient behavior of liquid jet expansion is quantified in the vicinity of the nozzle. It is observed that the liquid jet direction deviates from the hole axis already at the nozzle outlet, which is caused by internal flow characteristics.

In this study, the nonlinear pressure-flow characteristics of a spring-loaded pressure relief valve (PRV), which is used in the automotive fuel supply system for pressure control is analyzed, and its characteristics are improved by means of geometrical modifications of the valve structure. Given the complexity of the coupling mechanism between the valve internal flow characteristics and spring system, a quasi-steady computational fluid dynamics (CFD) method is introduced to predict the nonlinear pressure-flow characteristic curve of the valve and the accuracy is validated by experimental data. The total hydraulic force on the valve spool and diaphragm are divided into three parts according to the loading position and the correlation between the internal flow characteristics, hydraulic force, and pressure-flow characteristics of the valve are explained by CFD analysis and visualization. The results show that the quasi-steady CFD method can accurately predict the trends of the valve nonlinear pressure-flow characteristic curve, which is mainly determined by the hydraulic force produced in the middle chamber of the valve. When the valve opening reaches a certain value, a main vortex would be formed in the middle chamber and lead to the sudden increase of hydraulic force which causes the fluctuation of the pressure-flow characteristic curve of the valve. It is also found that the toggle point for the flow regimes seen in the valve is affected by the geometric structure of the middle chamber and the pressure-flow characteristics can be improved by the round corner size modification.

One of the challenges of hydraulic turbine design is the creation of a conveyor with high hydraulic performance in accordance with the parameters of the hydraulic energy. The blade inlet parameters, such as blade beta angle, lean angle, and ellipse axis ratio, have an effect on the performance and cavitation characteristics of the runner, among the numerous geometric elements that regulate turbine performance. All of these parameters must be optimized to ensure that the runner inlet is matched to the guide vane under design conditions and a wider range of off-design conditions. For hydraulic designers, computational fluid dynamics based performance prediction methods can provide rapid turbine performance predictions and expedite runner development. Finding a collection of accessible parameters, meanwhile, strongly depends on the designer’s previous design work, which is frequently time-consuming. In this article, the internal flow characteristics and energy performance of a Francis turbine with moderate specific-speed, as well as the blade leading edge geometrical parameters that influence them, are investigated in depth. The Francis turbine is designed in accordance with the rated head H (m), rated flow rate Q (m), and rated speed n (rpm) within the constraints of the fixed meridional projection, including the leading-edge and trailing-edge positions. The energy performance, internal flow characteristics, velocity profile, flow angles, pressure distribution, blade loading, and cavitation characteristics are computed, analyzed, and compared. The main findings can serve as a guide for the development of Francis turbines with moderate specific-speed.

Cavitation as a form of unsteady flow within centrifugal pumps can cause the reduced performance of pumps, disordered internal flow regimes, and flow loss. The present criterion used for determining the occurrence of cavitation is a 3% head drop. However, in most cases, pump cavitation already occurs with less than a 1%–2% head drop due to significant changes in the internal flow status. To examine changing patterns in internal flow characteristics as the degree of cavitation deepens in the early stage of cavitation in centrifugal pumps when the head curve does not show significant fluctuation, this paper focuses on a low specific speed centrifugal pump to analyze distributions of total internal pressure, speed, bubble volume, vortex structure, and entropy generation across different degrees of cavitation and obtain internal flow characteristics and flow loss patterns of pumps, with an aim of providing preferences for anti-cavitation hydraulic design of centrifugal pumps.

Influence of flashboard location on flow resistance properties and internal features of gate valve under the variable condition