Induced noise of impeller stuck and passive rotation state in multi-stage pump without power drive under natural flow conditions

The natural flow cooling strategy is commonly employed in modern high-speed vessels and nuclear-powered submarines. These vessels rely on the energy generated by their own speed to drive the cooling system and supply cooling water to the condenser. The circulating pump, which operates without a motor drive under natural flow conditions, is a large resistance component in the cooling system. However, it is also the primary noise source, significantly impacting the vessel’s safe operation and acoustic stealth performance. This study investigates the induced noise characteristics of a multi-stage pump under natural flow conditions by experiment, computational fluid dynamics (CFD), and acoustic finite element method. The analysis encompasses the distribution of the flow field, variations in acoustic power, spectral features of flow-induced noise, and directivity of external field radiation noise under different natural flow conditions. The results show that the acoustic power distribution is correlated with the flow field. When the impeller is stuck, the noise sources primarily concentrate in the flow separation area at the blade’s leading edge, the interface area between the impeller and the guide vane, and the flow shock area inside the guide vane. Conversely, when the impeller rotates passively, the blade wake area has a higher acoustic power. The flow noise spectrum under natural flow conditions mainly exhibits broadband and discrete characteristics. Additionally, the pump structure influences the external field radiation noise, and its directivity varies with different flow rates and characteristic frequencies. This study provides valuable insights into optimal design to reduce the noise of the circulating pump in the vessel’s natural flow cooling system. It is essential for ensuring the safe operation and acoustic stealth performance of high-speed vessels and nuclear-powered submarines.

Hydrodynamic modelling of flow impact on structures under extreme flow conditions

Apart from the direct threat to human lives, the flood waves as a result of the rapid catchment response to intense rainfall, breaches of flood defences, tsunamis or storm surges may induce huge impact forces on structures, causing structural damage or even failures. Most existing design codes do not properly account for these impact forces due to the limited understanding of the underlying physical processes and the lack of reliable empirical formulae or numerical approaches to quantifying them. This paper presents laboratory experiments to better understand the interaction between the extreme flow hydrodynamics and the hydraulic structures and uses the measured data to validate a numerical model. The model solves the two-dimensional shallow water equations using a finite volume Godunov-type scheme for the reliable simulation of complex flow hydrodynamics. New model components are developed for estimating the hydrostatic and hydrodynamic pressure to quantify the flow impact on structures. The model is applied to reproduce two selected experiment tests with different settings and satisfactory numerical results are obtained, which confirms its predictive capability. The model will therefore provide a potential tool for wider and more flexible field-scale applications.

Red soil for sediment capping to control the internal nutrient release under flow conditions

Nitrogen （N） and phosphorus （P） released from the sediment to the surface water is a major source of water quality impairment. Therefore, inhibiting sediment nutrient release seems necessary. In this study, red soil （RS） was employed to control the nutrients released from a black-odorous river sediment under flow conditions. The N and P that were released were effectively controlled by RS capping. Continuous-flow incubations showed that the reduction efficiencies of total N （TN）, ammonium （NH4＋-N）, total P （TP） and soluble reactive P （SRP） of the overlying water by RS capping were 77%, 63%, 77% and 92%, respectively, and nitrification and denitrification occurred concurrently in the RS system. An increase in the water velocity coincided with a decrease in the nutrient release rate as a result of intensive water aeration.

Platelet adhesion to the surface of a sudden tubular expansion tube under swirling flow condition

The size mismatch in an end-to-end vascular anastomosis between the host vessel and the graft may cause flow disturbance and predispose to thrombosis [1].Although a number of techniques have been employed to reduce the risk of anastomotic thrombosis due to the size mismatch。

Direct and noisy transitions in a model shear flow

The transition to turbulence in flows where the laminar profile is linearly stable requires perturbations of finite amplitude. ＂Optimal＂ perturbations are distinguished as extrema of certain functionals, and different functionals give different optima. We here discuss the phase space structure of a 2D simplified model of the transition to turbulence and discuss optimal perturbations with respect to three criteria： energy of the initial condition, energy dissipation of the initial condition, and amplitude of noise in a stochastic transition. We find that the states triggering the transition are different in the three cases, but show the same scaling with Reynolds number.

THE EFFECT OF THE NEGATIVE ENTROPY FLOW ON THE ORGANIZATION OF ATMOSPHERIC DISSIPATIVE STRUCTURES IN NON-EQUILIBRIUM CONDITIONS

The entropy balance equation that describes the entropy budget of atmospheric systems is derived from the Gibbs relation.The distribution of the entropy flows of a west-Pacific typhoon and a Bengal-Bay cyclone is calculated and thus the dissipativity of the atmospheric systems is revealed.

Magnesium degradation under physiological conditions - Best practice

This review focusses on the application of physiological conditions for the mechanistic understanding of magnesium degradation.Despite the undisputed relevance of simplified laboratory setups for alloy screening purposes,realistic and predictive in vitro setups are needed.Due to the complexity of these systems,the review gives an overview about technical measures,defines some caveats and can be used as a guideline for the establishment of harmonized laboratory approaches.

Study of Unforced Unsteadiness in Centrifugal Pump at Partial Flow Rates

In order to explore the unforced unsteadiness of centrifugal pumps,a 2-D frequency domain imaging display technology was used to study the development of these unsteady flow structures at partial flow conditions.The results showed that,the unsteady flow field was not only affected by rotor and stator interaction,but also appeared an unforced unsteadiness with fundamental frequency of St≈0.23 around the impeller throat area.Moreover,as the flow rates decreased,this unsteady flow structure gradually weakened and disappeared.When the flow rate was reduced to 0.6 times of design flow rate,another two unforced unsteady flow structures with characteristic frequencies of St≈0.0714 and St≈0.12 began to appear in the same area.Therefore,with the operating condition smaller than design flow rate,the internal flow became more and more complex.In addition to the forced unsteadiness,the unforced unsteadiness which is not connected with the blade passage frequency became more and more obvious.

Numerical simulation of two-dimensional viscous flows using combined finite element-immersed boundary method

In this paper, a method that combines the characteristic-based split finite element method（CBS-FEM） and the direct forcing immersed boundary（IB） method is proposed for the simulation of incompressible viscous flows. The structured triangular meshes without regarding the location of the physical boundary of the body is adopted to solve the flow, and the no-slip boundary condition is imposed on the interface. In order to improve the computational efficiency, a grid stretching strategy for the background structured triangular meshes is adopted. The obtained results agree very well with the previous numerical and experimental data. The order of the numerical accuracy is shown to be between 1 and 2. Moreover, the accuracy control by adjusting the number density of the mark points purely at certain stages is explored, and a second power law is obtained. The numerical experiments for the flow around a cylinder behind a backward-facing step show that the location of the cylinder can affect the sizes and the shapes of the corner eddy and the main recirculation region. The proposed method can be applied further to the fluid dynamics with complex geometries, moving boundaries, fluid-structure interactions, etc..

2-D CHARACTERISTICS LIKE MODEL AND OPEN BOUNDARY CONDITION FOR UNSTEADY OPEN CHANNEL FLOW MODELING

A characteristic like model is presented to calculate the two dimensional flow in open channels with finite or infinite dimensions. The comparisons between the computational results and experimental data show the model to be robust in simulating two dimensional unsteady flows. The comparisons also show the effectiveness of the open boundary condition in simulation of wave propagation process in an infinite domain with computational domain of finite dimension.

Navigable flow condition simulation based on two-dimensional hydrodynamic parallel model

Navigable flow condition simulations can provide detailed information on water depth and velocity distribution, simulation speed is one of the key factors which influence real-time navigation. In this paper, a navigable flow condition simulation system is developed to provide useful information for waterway management and shipping safety. To improve the simulation speed of 2-D hydrodynamic model, an explicit finite volume method and Open MP are used to realize parallel computing. Two mesh schemes and two computing platforms are adopted to study the parallel model＇s performance in the Yangtze River, China. The results show that the parallel model achieves dramatic acceleration, with a maximum speedup ratio of 34.94？. The parallel model can determine the flow state of the navigable channel in about 4 min, efficiency is further improved by a flow simulation scheme database. The developed system can provide early warning information for shipping safety, allowing ships to choose better routes and navigation areas according to real-time navigable flow conditions.

Improvement of signal processing in Coriolis mass flowmeters for gas-liquid two-phase flow

As an increasingly popular flow metering technology,Coriolis mass flowmeter exhibits high measurement accuracy under single-phase flow condition and is widely used in the industry.However,under complex flow conditions,such as two-phase flow,the measurement accuracy is greatly decreased due to various factors including improper signal processing methods.In this study,three digital signal processing methods—the quadrature demodulation(QD)method,Hilbert method,and sliding discrete time Fourier transform method—are analyzed for their applications in processing sensor signals and providing measurement results under gas-liquid two-phase flow condition.Based on the analysis,specific improvements are applied to each method to deal with the signals under two-phase flow condition.For simulation,sensor signals under single-and two-phase flow conditions are established using a random walk model.The phase difference tracking performances of these three methods are evaluated in the simulation.Based on the digital signal processor,a converter program is implemented on its evaluation board.The converter program is tested under single-and two-phase flow conditions.The improved signal processing methods are evaluated in terms of the measurement accuracy and complexity.The QD algorithm has the best performance under the single-phase flow condition.Under the two-phase flow condition,the QD algorithm performs a little better in terms of the indication error and repeatability than the improved Hilbert algorithm at 160,250,and 420 kg/h flow points,whereas the Hilbert algorithm outperforms the QD algorithm at the 600 kg/h flow point.

Necessary and sufficient condition of C^0 flows on closed surfaces with isolated singular points having the pseudo-orbit tracing property

IN this letter we discuss the necessary and sufficient condition of C^0 flows on closed surfaces with isolated singular points having the pseudo-orbit tracing property. According to ref. [1], on a closed surface, every minimal set of a C^r(r≥2) flow is trivial, but it is possible for a C^0 flow to contain non-trivial minimal sets. Thus C^0 flows on closed surfaces are more complicated than C^r(r≥2) flows.

Development mechanism of internal local corrosion of X80 pipeline steel

The occurrence and development mechanism of internal local corrosion has always been a controversial topic,and especially under flow conditions.In this paper,an improved high shear force loop was experimentally used,and local flow field is induced by simulating corrosion defects on the surface of X80 pipeline steel specimens.The characteristics of corrosion products deposited on the surface of specimens in CO2-saturated NACE solution were investigated by means of electrochemical impedance spectroscopy(EIS),scanning electron microscopy(SEM),X-ray diffraction(XRD),and energy dispersive spectrometry(EDS).The 3D micromorphology of the corrosion test surface after remove the corrosion scale used to measure the size of localized corrosion pit.Under the influence of local defects,the wall shear stress(WSS)and turbulent kinetic energy of local flow fields enhanced significantly,and pressure fluctuations in local flow field were induced.The results showed that the characteristics of surface corrosion products varied with flow velocity.The corrosion scales formed in various regions of specimens with defects exhibited different surface micro-morphologies and chemical compositions.Overall,these data offer new perspectives for better understanding the mechanisms behind local corrosion.

Experimental hydrodynamic study of the Qiantang River tidal bore

To study the hydrodynamics of tidal bore, a physical modeling study is carried out in a rectangular flume with considera- tions of the tidal bore heights, the propagation speeds, the tidal current velocities, the front steepness, and the bore shapes. After the validation with the field observations, the experimental results are analyzed, and it is shown that： （1） the greater initial ebb velocity or the larger initial water depth impedes the tidal bore propagation, （2） the maximum bore height appears at an initial ebb velocity in the range of 0.5 m/s-l.5 m/s. （3） when the Froude number exceeds 1.2, an undular bore appears, atter it exceeds 1.3, a breaking bore occurs, and after it exceeds 1.7, the bore is broken.

Dual-targeting nanovesicles enhance specificity to dynamic tumor cells in vitro and in vivo via manipulation of αvβ3-ligand binding

The dynamic or flowing tumor cells just as leukemia cells and circulating tumor cells face a microenvironment difference from the solid tumors,and the related targeting nanomedicines are rarely reported.The existence of fluidic shear stress in blood circulation seems not favorable for the binding of ligand modified nanodrugs with their target receptor.Namely,the binding feature is very essential in this case.Herein,we utilized HSPC,PEG-DSPE,cholesterol and two avb3 ligands(RGDm7 and DT4)with different binding rates to build dual-targeting nanovesicles,in an effort to achieve a"fast-binding/slow-unbinding"function.It was demonstrated that the dual-targeting nanovesicles actualized effi-cient cellular uptake and antitumor effect in vitro both for static and dynamic tumor cells.Besides,the potency of the dual-targeting vesicles for flowing tumor cells was better than that for static tumor cells.Then,a tumor metastasis mice model and a leukemia mice model were established to detect the killing ability of the drug-loaded dual-targeting vesicles to dynamic tumor cells in vivo.The therapy efficacy of the dual-targeting system was higher than other controls including single-targeting ones.Generally,it seems possible to strengthen drug-targeting to dynamic tumor cells via the control of ligandereceptor interaction.

Landmarks in the application of electrical tomography in particle science and technology

Selected milestones in the development and use of electrical tomography in powder conveying, slurry processing and multi-phase flow are highlighted. The ability to map concentration in opaque mixtures under process-realistic conditions was a major innovation for the method and has had far reaching implications. Subsequent developments have enabled velocity information to be abstracted resulting in the ability to measure component flux and motion.

A note on a boundary condition for spouted beds

The boundary condition, zero solids pressure at the top of a particle bed of maximum spoutable height, Hm, is shown to eliminate any resort to empiricism in the derivation of the fluid velocity in the annulus of a spouted bed for which both viscous and inertial effects are taken into account. The same boundary condition fails when applied to a spouted bed for which the bed height H 〈 Hm, especially when H 〈 0.8Hm.