Sinusoidal Flow Research Articles

A New Research Scheme for Full-Scale/Model Test Comparison of Wind Effects on Pengcheng Cooling Tower Based on Sinusoidal Flow Field Simulations

When examining the history of wind engineering, it is evident that many full-scale/model test comparisons have found noticeable differences between the results. Although understanding the causes of these differences is important for practical purposes, limited numerical and experimental conditions have often resulted in subjective explanations for full-scale/model test comparisons without scientific validation. To address this issue, this article suggests the use of the computational fluid dynamics technique or the multiple-fan actively controlled wind tunnel technique to quantitatively reveal the adverse effects that impact the reliability of the traditional atmospheric boundary layer wind tunnel tests for a large cooling tower, including not only the widely acknowledged influences (Reynolds number effects and turbulent flow characteristics effects) but also the non-stationarity effects that have potential influences. Established on the novel proposition, a new research scheme for future full-scale/model test wind effects comparisons for large cooling towers has been formulated based on the numerical or physical simulations of the sinusoidal flow fields. Using the Pengcheng cooling tower as a case study, the research recognized the very significant impact of Reynolds number effects, the non-stationarity effects that cannot be ignored, and the negligible effects of turbulent flow characteristics.

The Effect of Spatial Velocity Gradients on Block-Matching Accuracy for Ultrasound Velocimetry

Block matching serves as the foundation for ultrasound velocimetry techniques such as blood speckle tracking and echo-particle image velocimetry. Any spatial velocity gradients (SVGs) inside a block-matching pair will result in tracking error, due to both the finite block size and the ultrasound point-spread-function. We assess, using an in silico sinusoidal flow phantom, the effect of SVG magnitude and beam-to-flow angle on block-matching bias and precision. Secondarily we assess the effect that SVGs have on velocimetry bias when using angled plane-wave compounding. The magnitude and angle of SVGs were varied by adjusting the wavelength and direction of a sinusoidal flow profile. Scatterers displaced by this flow profile were used for simulating ultrasound radio frequency data at discrete time points. After beamforming, the 2-D flow field was estimated using block matching. Two imaging sequences were tested, a single plane-wave and a three-angled plane-wave. Smaller sinusoidal flow wavelengths resulted in increased bias and reduced precision, revealing an inverse relationship between sinusoidal flow wavelength and tracking error, with median errors ranging from 69%-90% for the smallest flow wavelengths (highest SVGs) down to 3%-5% for the largest (lowest SVGs). The SVG angle was also important, in which lateral SVGs (with axially oriented flows) resulted in significant speckle decorrelation and high tracking errors in regions with high SVGs. Conversely, axial SVGs (laterally oriented flow) experienced higher bias in the peak velocity regions of the flow profile. Coherent compounding resulted in higher velocity errors than using a single transmission for lateral SVGs but not for axial SVGs. The highest SVGs that could be measured with ≤10% error was when the sinusoidal flow wavelength was less than 20 times the ultrasound pulse wavelength. The clinical significance is that the high SVGs present in high kinetic energy flows, such as severe carotid stenosis and aortic regurgitation, will limit the ability to accurately quantify the velocities in these flow structures.

Analysis of the viability of a radial Double Decker Turbine for application in Oscillating Water Column devices

Oscillating Water Column (OWC) devices are the most widespread among the different systems developed to harness the wave energy available on our coasts. Air turbines, normally used as Power Take Off (PTO) in these devices, are their most controversial part. Unidirectional turbines were first used with rectifying valves to take advantage of both characteristic operating stages of the OWC: exhalation and inhalation. The use of valves was quickly discarded and bidirectional turbines, which rotate in the same direction regardless whence the flow comes, were adopted as the most common solution despite reaching lower efficiencies than unidirectional ones. The Twin Turbine Configuration (TTC), based on the use of two unidirectional turbines, emerged then as a promising system, its main drawback being the duplicity of the equipment. The Double Decker Turbine (DDT) concept has been recently introduced to overcome these limitations since it combines in a single design the two typical solutions: self‐rectifying behaviour and the use of unidirectional turbines. In this work, the performance of a radial DDT, composed of an InFlow Radial (IFR) turbine and an OutFlow Radial (OFR) turbine, is assessed. A CFD model is used to design and optimize an IFR turbine to be mounted in combination with an OFR turbine taken from the literature. Finally, a non‐steady analysis is carried out assuming sinusoidal flow conditions. Results demonstrate that this radial version of the DDT could compete with its axial version and with other alternatives.

Numerical analysis of the effects of interconnector design and operating parameters on solid oxide fuel cell performance

Fuel cells can provide higher electrical conversion efficiency than traditional coal-fired power plants and electric generators based on internal combustion engines. In addition, high-efficiency solid oxide fuel cells (SOFC) have two specific advantages compared with other fuel cells as a result of their high-temperature operation. First, SOFCs are compatible with various fuels, ranging from hydrogen to CO and hydrocarbons. Second, SOFCs generate significant amounts of exhaust heat that can be used in combined heat and power systems. Furthermore, SOFCs have quiet and vibration-free operation, eliminating the noise typically associated with power generation systems. These fuel cells also produce no or very low levels of SO2 and NO emissions. In this study, we numerically investigated the performance of a planar SOFC with different interconnector designs at various operating temperatures. Multiple parameters were considered, such as interconnection geometries, anode and cathode materials, operating temperatures, and flow rates. As a result, the horizontal sinusoidal flow channel geometry, operating temperature of 600 °C, hydrogen gas flow rate of 86.5 SCCM/min, and oxygen gas flow rate of 28.75 SCCM/min, NiO anode material, and LSCF cathode material provided the greatest performance in terms of energy and current density.

Nonlinear stability of sinusoidal Euler flows on a flat two-torus

Nonlinear stability of sinusoidal Euler flows on a flat two-torus

Mapping dynamical systems with distributed time delays to sets of ordinary differential equations

Real-world dynamical systems with retardation effects are described in general not by a single, precisely defined time delay, but by a range of delay times. An exact mapping onto a set of N + 1 ordinary differential equations exists when the respective delay distribution is given in terms of a gamma distribution with discrete exponents. The number of auxiliary variables one needs to introduce, N, is inversely proportional to the variance of the delay distribution. The case of a single delay is therefore recovered when . Using this approach, denoted here the ‘kernel series framework’, we examine systematically how the bifurcation phase diagram of the Mackey–Glass system changes under the influence of distributed delays. We find that local properties, f.i. the locus of a Hopf bifurcation, are robust against the introduction of broadened memory kernels. Period-doubling transitions and the onset of chaos, which involve non-local properties of the flow, are found in contrast to be more sensitive to distributed delays. In general, the observed effects are found to scale as . Furthermore, we consider time-delayed systems exhibiting chaotic diffusion, which is present in particular for sinusoidal flows. We find that chaotic diffusion is substantially more pronounced for distributed delays. Our results indicate in consequence that modeling approaches of real-world processes should take the effects of distributed delay times into account.

Response of a novel denitrifying phosphorus removal (AAO-BCO) system to sinusoidal flow perturbation of municipal sewage: Adaptability, tolerance and improvement

To date, studies on the effect of sewage disturbances on treatment facilities were based on fixed-length flow variations, which are incapable of imitating the actual dynamic flow characteristics of municipal sewage. Here, an innovative dynamic influent disturbance control system is established in this study and applied in a novel denitrifying phosphorus removal (anaerobic anoxic oxic-biological contact oxidation, AAO-BCO) system to simulate seasonal and diurnal sewage fluctuations in laboratory-scale experiments. The results showed that, under sinusoidal influent flow perturbation, the effluent pollutant content followed a relatively gentle sinusoidal trend and did not always result in desired level of pollutant removal. The ability of the system to cope with sinusoidal flow variations was susceptible to the amplitude of diurnal sewage fluctuation, while stronger tolerance capacity was observed to seasonal and momentary increase in wastewater flowrate. There was also a discrepancy in the system buffering capacity towards various pollutants removal (COD > TIN > PO43−), which may be attributed to wide fluctuations in PO43−/NO3− and different decrease in metabolic activity of denitrifying phosphorus removal (DPR) sludge caused by extreme hydraulic retention times. To improve the robustness and stability of the DPR system, a regulating strategy was proposed to alleviate the biomass reduction and uncoordinated PO43−/NO3−.

Streamwise sinusoidal flow over two identical tandem circular cylinders

This study conducts three-dimensional large eddy simulations at a subcritical Reynolds number of 103 to investigate the effects of sinusoidal streamwise flow on the flow structure, Strouhal number, and aerodynamic forces of two tandem circular cylinders. The center-to-center spacing L between the two cylinders is fixed at 3.5D, where D is the cylinder diameter. The velocity U of sinusoidal streamwise flow is set as U* = U/U0 = 1 + A*sin(2π(f*U0/D)t), where A* denotes the velocity amplitude ratio, and f* ((fuD/U0)/St0) denotes the non-dimensional frequency of sinusoidal flow, with fu being the frequency of sinusoidal flow and St0 being the Strouhal number of two tandem cylinders with L/D = 3.5 under the uniform approaching flow. The results show that the variations of f* (0–2.67) and A* (0–0.25) lead to the generation of not only the reattachment and coshedding flows independently but also their joint flow involving intermittent occurrences of the reattachment and coshedding flows. A map of the dependence of the flow structure on f* and A* is presented, marking the borders of various flow patterns in the f* − A* plane. Flow separation, Strouhal number, and aerodynamic forces on the two cylinders are found to be sensitive to f* and A*, exhibiting distinct variations following the flow structures. A time-frequency analysis of the bistable pattern is presented, identifying the two distinct vortex-shedding frequencies and confirming the time dependence and bi-stability of the bistable flow.

Optimal design of a cathode flow field for performance enhancement of PEM fuel cell

Flow field design plays a key role in enhancing the performance of proton exchange membrane fuel cell (PEMFC). In this work, the cathode flow field is optimized to enhance the performance of PEMFC by improving the capacity of mass transfer and water removal, and a three-dimensional, two-phase, isothermal numerical model is established to evaluate its performance. Additionally, visualization experiment is carried out to verify the simulation results. It shows that the opposite sinusoidal wave flow fields (OSWFFs) with single-inlet, dual-inlet and the block provide 6.86%, 1.26%, and 2.31% performance enhancement, respectively, compared with the parallel flow fields (PFFs), which positively affects the mass transfer capacity and water removal performance. Among them, the dual-inlet OSWFF with block is the most helpful for performance enhancement, with an enhancement of 9.30% at 2.2 A cm−2 compared to the PFF. Moreover, Pearson correlation coefficient (PCC) is proposed for the first time to evaluate the correlation between each index and PEMFC performance. The comparison of stoichiometric ratios shows that the more significantly correlated indexes contribute to the dual-inlet OSWFF outperforming the single-inlet OSWFF at high inlet velocities, verifying the applicability of PCC in PEMFC.

Study on flow characteristics of gas-liquid-solid circulating fluidized bed with central sinusoidal pulsating flow

Study on flow characteristics of gas-liquid-solid circulating fluidized bed with central sinusoidal pulsating flow

Double diffusion and Hall effects on MHD sinusoidal natural convection flow of silver water-based nanofluid from a porous vertical plate

This paper scrutinizes Hall current, Soret and Dufour impacts on natural convective flow of nanofluid attributable to variation in sinusoidal surface temperature over a vertical plate through a porous medium with strong transverse magnetic field applied normally to the flow. In this regard, the silver metal is considered as nanoparticles with water as base fluid. The overlapping multi-domain bivariate spectral local linearization method (OMD-BSLLM) has been utilized to solve the dimensionless governing equations which are attained by means of appropriate transformations. The obtained results are portrayed via graphical and tabular formations to inspect flow fields, shear stresses, heat and mass transmission characteristics for varying thermo-physical parameters. We found that there is an enhancement in the flow fields, shear stresses and heat transportation with the use of silver nanoparticles. Thermal and concentration boundary layer thickness enhance by using porous material, whereas diminish with improvement in Hall effect and ratio of buoyancy forces. The flow characteristics decline with the inclusion of porous medium while elevates with increment in Hall parameter. Moreover, an upgrade in thermal-diffusion correspond to a substantial growth in concentration field along with mass transfer rate. Current analysis can be useful in MHD energy generators, and industrial applications such as heating and cooling procedures owing to the involvement of nanoparticles having superior thermal conductivity features.

Selection of vortex ripple dimensions in sinusoidal oscillatory flows. Part 1. Ripple dimensions and fluid kinematics

Subaqueous vortex ripples in equilibrium are characterized by their unique geometry and dimensions. Motivated by the recent direct numerical simulation study of oscillatory turbulent flow over a wavy bottom by Önder & Yuan (J. Fluid Mech., vol. 858, 2019, pp. 264–314), the objective of this study is to further investigate the fluid dynamical controls that determine the distinctive equilibrium dimensions of vortex ripples. We use direct numerical simulations to investigate the differences in flow kinetics between sinusoidal oscillatory flow over equilibrium and out-of-equilibrium vortex ripples. In comparison with the equilibrium case, the spanwise coherent vortices, the averaged bottom shear stress on overlying flow and the shear stress distribution on the ripple surface are identified as the key fluid dynamical controls on equilibrium dimensions. Based on these controls, we propose mechanisms in the selection of vortex ripple dimensions. We observe that the flow adjusts in such a way that the interaction between overlying flow and vortex ripples tends to generate the strongest coherent vortices while the ripple surface (or overlying flow) experiences the smallest shear stress averaged over ripple wavelength during the selection process. Through a triple decomposition of the flow, the component of the ripple-induced fluctuation is found to dictate these fluid dynamical controls, which implies that this component plays an important role in the evolution of vortex ripples.

Optimization and evaluation criteria of water-gas transport performance in wave flow channel for proton exchange membrane fuel cell

Flow channel optimization is an important method to improve the water-gas transport capacity and enhance the performance of proton exchange membrane fuel cells. In this study, the size ratio of the opposite sinusoidal wave flow channel (OSWFC) is optimized, and three-dimensional numerical models are developed to evaluate the comprehensive performance. The results show that OSWFCs obtain performance enhancement compared to the parallel flow channel. 1:1 wave channel has a maximum improvement of 19.53% in mass transfer capacity by the most frequent flow disturbance, while 1:3 has a maximum increasement of 37.5% in water removal performance by the virtue of gentle wave structure. Large pressure loss decreases the mass transfer efficiency, although it with the maximum mass transfer capacity, the mass transfer evaluation criterion of 1:1 wave channel is less than that of 1:3. Moreover, a significant correlation between water-gas transport capacity and electrochemical performance is demonstrated by Pearson correlation coefficient.

Non-local Effects in Inhomogeneous Flows of Soft Athermal Particles

We study non-local effects on inhomogeneous flows of soft athermal particles near the jamming transition. We employ molecular dynamics simulations to demonstrate Kolmogorov flows, where a sinusoidal flow profile with fixed wave number is externally imposed, resulting in a spatially inhomogeneous shear rate. We find that the rheology of soft athermal particles is strongly wave number-dependent and particle migration is not sufficient to explain the resulting stress profiles within conventional local constitutive relations. We show that stress profiles can be described by non-local constitutive relations that account for gradients to fourth order.

Experimental performance of proton exchange membrane fuel cell with novel flow fields and numerical investigation of water-gas transport enhancement

The performance of the proton exchange membrane fuel cell (PEMFC) depends on the water-gas transport capacity of flow fields. In this paper, the performance of the designed PEMFC with novel flow fields is tested by experimental methods. The experimental results show that the PEMFC with opposite sinusoidal wave flow field (OSWFF) and intercepted flow field (ICFF) are improved compared to the parallel flow field. The PEMFC with single-inlet OSWFF and ICFF show 19% and 11% performance enhancement at 2.0 A cm−2, respectively. A 3D numerical model for the validation experiment is established to analyze the water-gas transport characteristics of the flow field. The mass transfer performance of ICFF with 3D structural optimization is much better than that of OSWFF with 2D structural optimization, and the effective mass transfer coefficient and efficiency evaluation criterion are improved by 106% and 258%, respectively. The 7% improvement in oxygen uniformity in the dual-inlet mode compared to the single-inlet mode enhances the stability of the electrochemical reaction and the 28% improvement in velocity uniformity, which contributes to the uniform distribution and discharge of liquid water, which in turn enhances the PEMFC performance.

Effects of oscillating gas-phase flow on an evaporating multicomponent droplet

The dynamics of an evaporating droplet in an unsteady flow is of practical interest in many industrial applications and natural processes. To investigate the transport and evaporation dynamics of such droplets, we present a numerical study of an isolated droplet in an oscillating gas-phase flow. The study uses a one-way coupled two-phase flow model to assess the effect of the amplitude and the frequency of a sinusoidal external flow field on the lifetime of a multicomponent droplet containing a non-volatile solute dissolved in a volatile solvent. The results show that the evaporation process becomes faster with an increase in the amplitude or the frequency of the gas-phase oscillation. The liquid-phase transport inside the droplet also is influenced by the unsteadiness of the external gas-phase flow. A scaling analysis based on the response of the droplet under the oscillating drag force is subsequently carried out to unify the observed evaporation dynamics in the simulations under various conditions. The analysis quantifies the enhancement in the droplet velocity and Reynolds number as a function of the gas-phase oscillation parameters and predicts the effects on the evaporation rate.

Scale dependence of near-inertial wave’s concentration in anticyclones

Near-inertial waves (NIWs), pervasive and dominating the mixing process in the upper ocean, are observed to concentrate in anticyclones. Based on the NIW amplitude equation derived by Young & Ben Jelloul, which captures dispersion and effects of vortical flow’s advection and refraction, this work analytically and numerically studies the influence of scale on the concentration of NIWs. For a sinusoidal background shear flow, the exact solutions expressed as periodic Mathieu functions are approximated by a Gaussian envelope with Hermite polynomial oscillations to determine the distance to the anticyclones. Two dimensionless parameters control NIW’s dynamics: (i) h/Ψ, where h is a constant capturing the strength of wave dispersion and Ψ is the magnitude of the background streamfunction capturing the ratio of dispersion to refraction; (ii) LΨ/LM, the ratio between the spatial scales of background flow and NIWs, where LΨ and LM, respectively, captures the relative strength between advection and refraction. The refraction by the background flow leads to the concentration in the regions with negative vorticity, dispersion controls the variance of the wave packet, and the advection shifts the center of NIWs away from the peak of negative vorticity, which is scale-dependent. When the refraction effect dominates, i. e., small LΨ/LM, NIWs concentrate in anticyclones, and this concentration becomes stronger as h/Ψ decreases; when the advection effect dominates, i.e., large LΨ/LM, the NIW’s concentration is less obvious. Numerical simulations with backgrounds of sinusoidal shear, vortex quadrupoles and random vortices confirm these results. Considering the similarity between the NIW amplitude equation and the Schrödinger equation, we propose a new perspective that the combined effect of uncertainty relation and energy conservation leads to large-scale NIW’s concentration in anticyclones.

DDPM simulation of the erosion of immersed tubes in a pulsating fluidized bed

In this study, the effects of the type of pulsating inlet waveform, pulsation frequency, and pulsation amplitude on the stability of fluidized beds and the erosion of immersed tubes were investigated by numerical simulation. Compared with rectangular and triangular inlet flows, sinusoidal flow induced the lowest immersed-tube erosion rate and pressure-drop fluctuation in the fluidized bed. Furthermore, under sinusoidal flow with a pulsation frequency of 1 Hz and pulsation amplitude of 0.25um, the immersed-tube erosion rate was lower by 1.8 %, standard deviation of pressure drop by 14.16 %, and energy generated from bubble rupture by 47.83 % than those under uniform flow. A dimensionless parameter χp that can represent immersed-tube erosion during pulsating flow was proposed, which reflects the effect of particle flow characteristics, particle fluidization degree, and pulsation frequency on immersed-tube erosion.

Effects of oscillation frequency on the flow characteristics of a centrifugal pump impeller with sinusoidal flow rate

This study uses large eddy simulation to investigate the flow characteristics of a centrifugal pump impeller with sinusoidal flow rate and constant rotational speed. Five different oscillation frequencies ( f/f0 = 1.0, 1.2, 1.5, 2.0, and 3.0, where f0 indicates one-ninth of the rotational speed) are selected to isolate the influence of oscillation frequency on the flow characteristics. Studies show that the pressure deviation between dropping and rising stages concentrates at the impeller inlet at instantaneous 0.5 Qd ( Qd is the design load), and its value increases with the increase in oscillation frequency. The lowest period of many flow characteristics, including pressure fluctuation and head, equals to that of flow rate. The differences in pressure fluctuation between adjacent channels decreases with the increase in oscillation frequency. The first and second dominant frequencies of pressure fluctuation are mainly affected by the oscillation frequency in the nonstall passage, and they have an important relationship with the stall vortex in the stall passage. With the increase in oscillation frequency, the amplitude of lowest order head pulsation increases, and the high order head pulsation gradually weakens. The average head is approximately 2.36 m.

Mechanobiology in the development and progression of non-alcoholic fatty liver disease: an updated review

Mechanobiology is a rapidly emerging field focused on the biological impact of physical forces at the molecular, cellular, and tissue level. Living cells perceive mechanical cues and transform them into biochemical signals through mechanotransduction. Mechanotransduction is a complex process that involves mechanosensors (which are located in the plasma membrane or within the cell) and mechanotransmission to the nucleus (which occurs either by physical connection between the mechanosensor and the nucleus or by mechanosignaling through biochemical pathways). Essential biological functions, including development, growth, motility, and metabolism, depend on the mechanoresponses generated by these events. Multiple lines of evidence indicate that disruption of mechanical homeostasis may contribute to the pathogenesis of non-alcoholic fatty liver disease (NAFLD), a highly prevalent metabolic disorder characterized by abnormal accumulation of lipid droplets in hepatocytes (steatosis) and often associated with inflammation and liver cell injury (steatohepatitis). While predicting individual predisposition to adverse outcomes in NAFLD remains a challenge, there is increasing evidence that steatosis and steatohepatitis trigger mechanoresponses that contribute to the early stages of pathogenesis in NAFLD and critically impact disease progression. Lipid accumulation and lipotoxicity modify liver viscoelasticity, alter the biomechanics of liver sinusoids, and initiate aberrant pathways of mechanotransduction in hepatocytes and non-parenchymal liver cells, such as sinusoidal endothelial cells and hepatic stellate cells. Interactions of these cells at mechanical interfaces with each other, with extracellular matrix, and with sinusoidal blood flow are profoundly altered by steatosis and steatohepatitis; such changes may promote a pro-angiogenic and pro-fibrotic milieu. A better understanding of liver mechanobiology may facilitate the identification of novel molecular and cellular targets in the management of NAFLD.