Flow Dynamics Research Articles

Investigating Pressure Gradient Dynamics in Two-phase Fluid Flow through Porous Media: An Experimental and Numerical Analysis

Investigating Pressure Gradient Dynamics in Two-phase Fluid Flow through Porous Media: An Experimental and Numerical Analysis

Time-Resolved Dynamic Optical Coherence Tomography for Retinal Blood Flow Analysis.

Optical coherence tomography (OCT) representations in clinical practice are static and do not allow for a dynamic visualization and quantification of blood flow. This study aims to present a method to analyze retinal blood flow dynamics using time-resolved structural OCT. We developed novel imaging protocols to acquire video-rate time-resolved OCT B-scans (1024 × 496 pixels, 10 degrees field of view) at four different sensor integration times (integration time of 44.8 µs at a nominal A-scan rate of 20 kHz, 22.4 µs at 40 kHz, 11.2 µs at 85 kHz, and 7.24 µs at 125 kHz). The vessel centers were manually annotated for each B-scan and surrounding subvolumes were extracted. We used a velocity model based on signal-to-noise ratio (SNR) drops due to fringe washout to calculate blood flow velocity profiles in vessels within five optic disc diameters of the optic disc rim. Time-resolved dynamic structural OCT revealed pulsatile SNR changes in the analyzed vessels and allowed the calculation of potential blood flow velocities at all integration times. Fringe washout was stronger in acquisitions with longer integration times; however, the ratio of the average SNR to the peak SNR inside the vessel was similar across all integration times. We demonstrated the feasibility of estimating blood flow profiles based on fringe washout analysis, showing pulsatile dynamics in vessels close to the optic nerve head using structural OCT. Time-resolved dynamic OCT has the potential to uncover valuable blood flow information in clinical settings.

On the prediction of the turbulent flow behind cylinder arrays via Echo State Networks

Abstract This study aims at the prediction of the turbulent flow behind cylinder arrays by the application of Echo State Networks (ESN). Three different arrangements of arrays of seven cylinders are chosen for the current study. These represent different flow regimes: single bluff body flow, transient flow, and co-shedding flow. This allows the investigation of turbulent flows that fundamentally originate from wake flows yet exhibit highly diverse dynamics. The data is reduced by Proper Orthogonal Decomposition (POD) which is optimal in terms of kinetic energy. The Time Coefficients of the POD Modes (TCPM) are predicted by the ESN. The network architecture is optimized with respect to its three main hyperparameters, Input Scaling (INS), Spectral Radius (SR), and Leaking Rate (LR), in order to produce the best predictions in terms of Weighted Prediction Score (WPS), a metric leveling statistic and deterministic prediction. In general, the ESN is capable of imitating the complex dynamics of turbulent flows even for longer periods of several vortex shedding cycles. Furthermore, the mutual interdependencies of the TCPM are well preserved. However, optimal hyperparameters depend strongly on the flow characteristics. Generally, as flow dynamics become faster and more intermittent, larger LR and INS values result in better predictions, whereas less clear trends for SR are observable.

Spatiotemporal dynamics of cortical somatosensory network in typically developing children.

Sense of touch is essential for our interactions with external objects and fine control of hand actions. Despite extensive research on human somatosensory processing, it is still elusive how involved brain regions interact as a dynamic network in processing tactile information. Few studies probed temporal dynamics of somatosensory information flow and reported inconsistent results. Here, we examined cortical somatosensory processing through magnetic source imaging and cortico-cortical coupling dynamics. We recorded magnetoencephalography signals from typically developing children during unilateral pneumatic stimulation. Neural activities underlying somatosensory evoked fields were mapped with dynamic statistical parametric mapping, assessed with spatiotemporal activation analysis, and modeled by Granger causality. Unilateral pneumatic stimulation evoked prominent and consistent activations in the contralateral primary and secondary somatosensory areas but weaker and less consistent activations in the ipsilateral primary and secondary somatosensory areas. Activations in the contralateral primary motor cortex and supramarginal gyrus were also consistently observed. Spatiotemporal activation and Granger causality analysis revealed initial serial information flow from contralateral primary to supramarginal gyrus, contralateral primary motor cortex, and contralateral secondary and later dynamic and parallel information flows between the consistently activated contralateral cortical areas. Our study reveals the spatiotemporal dynamics of cortical somatosensory processing in the normal developing brain.

Computational Evaluation of Pulsating Heat Pipe for Fluid Flow Behavior and its Thermal Performance

Computational fluid analysis of a single circuit heat pipe was undertaken to ascertain the thermal efficiency of water at various fill ratios, specifically 40%, 50%, and 60% under varying heating conditions. The analysis employed the ANSYS Fluent computational fluid dynamics software, utilizing a k-epsilon to the heat pipe as the solver. The analysis was carried out on a copper tube with an internal diameter measuring 3/16 inches. During the analysis, the thermal inflow at the adiabatic region was adjusted to zero, while the condenser region’s temperature remained constant at 25°C. Meanwhile, the heat input at the evaporator region was systematically adjusted to 105°C, 110°C, 115°C, and 120°C. Key Performance characteristics of heat pipe i.e. thermal resistance, and water volume fraction were evaluated during analysis. The temperature variations noted in both regions affirmed that the pulsating pipe’s performance was influenced by the phase transition between liquid and vapor. Furthermore, the concentration of volume within the evaporator section was monitored, confirming the presence of a dual-phase phenomenon within the heat pipe. Through the analysis, it was noted that the thermal resistance of the water is minimized at a 50% fill ratio for each level of heat input. Notably, the promising results were obtained at an input temperature of 120°C with a value of 1.025°C /W which was 7.3% and 9.8% lower than thermal resistance at 40% and 60% fill ratios, respectively. The reduced thermal resistance in this scenario is attributed to the flow dynamics within the capillary, propelled by rapid phase change mechanisms. This shows the importance of Pulsating Heat Pipes (PHPs) in thermal control, as well as the intricacies of their operating mechanisms. Experimental and theoretical investigations have investigated numerous elements influencing PHP performance, with numerical modeling providing insight into thermal resistance and water volume fraction dynamics under varying heating temperatures and fill ratios.

Heterogeneity in Permeability and Particulate Organic Carbon Content Controls the Redox Condition of Riverbed Sediments at Different Timescales

AbstractThe hydrological and biogeochemical properties of the hyporheic zone in stream and riverine ecosystems have been extensively studied over the past two decades. Although it is widely acknowledged that sediment heterogeneity can influence biogeochemical reactions, little effort has been made to understand the role of heterogeneity on the spatiotemporal variability of riverbed redox conditions under changing flow dynamics at different timescales. Here we integrate a mechanistic model and field data to demonstrate that heterogeneity in permeability plays a vital role in modulating sediment redox conditions at both seasonal (annual) and event (daily‐to‐weekly) timescales, whereas heterogeneity in particulate organic carbon (POC) content only has a comparable influence on redox conditions at the seasonal timescale. These findings underscore the importance of accurately characterizing sediment heterogeneity, in terms of permeability and POC content, in quantifying biogeochemical dynamics in the riverbed and hyporheic zones of riverine ecosystems.

Numerical investigation of the unsteady flow and wave dynamics in a wave rotor combustor

Numerical investigation of the unsteady flow and wave dynamics in a wave rotor combustor

Swirling Capillary Instability of Rivlin–Ericksen Liquid with Heat Transfer and Axial Electric Field

The mutual influences of the electric field, rotation, and heat transmission find applications in controlled drug delivery systems, precise microfluidic manipulation, and advanced materials’ processing techniques due to their ability to tailor fluid behavior and surface morphology with enhanced precision and efficiency. Capillary instability has widespread relevance in various natural and industrial processes, ranging from the breakup of liquid jets and the formation of droplets in inkjet printing to the dynamics of thin liquid films and the behavior of liquid bridges in microgravity environments. This study examines the swirling impact on the instability arising from the capillary effects at the boundary of Rivlin–Ericksen and viscous liquids, influenced by an axial electric field, heat, and mass transmission. Capillary instability arises when the cohesive forces at the interface between two fluids are disrupted by perturbations, leading to the formation of characteristic patterns such as waves or droplets. The influence of gravity and fluid flow velocity is disregarded in the context of capillary instability analyses. The annular region is formed by two cylinders: one containing a viscous fluid and the other a Rivlin–Ericksen viscoelastic fluid. The Rivlin–Ericksen model is pivotal for comprehending the characteristics of viscoelastic fluids, widely utilized in industrial and biological contexts. It precisely characterizes their rheological complexities, encompassing elasticity and viscosity, critical for forecasting flow dynamics in polymer processing, food production, and drug delivery. Moreover, its applications extend to biomedical engineering, offering insights crucial for medical device design and understanding biological phenomena like blood flow. The inside cylinder remains stationary, and the outside cylinder rotates at a steady pace. A numerically analyzed quadratic growth rate is obtained from perturbed equations using potential flow theory and the Rivlin–Ericksen fluid model. The findings demonstrate enhanced stability due to the heat and mass transfer and increased stability from swirling. Notably, the heat transfer stabilizes the interface, while the density ratio and centrifuge number also impact stability. An axial electric field exhibits a dual effect, with certain permittivity and conductivity ratios causing perturbation growth decay or expansion.

Interfacial dynamics of two immiscible second-grade and couple stress fluids in rotating and counter-rotating scenarios

This article aims to examine the dynamics of interfacial flow that occurs when a layer of second-grade fluid rotates over another layer of uniformly rotating immiscible couple stress fluid. Fluid models with different densities, pressures, velocities, and viscosities exhibit intriguing flow properties. Under the restriction of parameter σ2ρ=1 , where σ=ω2/ω1 (angular velocities ratio) and ρ=ρ2/ρ1 (densities ratio), the occurrence of similarity solutions under coupling and viscoelastic effects across the interface for both cases of co-and-counter rotation is investigated. In contrast to the rotation of upper fluid, the couple stress fluid layer can counter-rotate. An advanced numerical method known as the Keller box is employed to thoroughly analyze the multiple aspects of the flow. The dominance of the couple stress fluid has been observed in shaping the dynamics of interfacial flow, significantly impacting phenomena such as the generation of inward/outward jets, Ekman pumping/suction, and the development of recirculation regions. Lower-layer far-field flow demonstrates transitions, oscillating between inflow and outflow, depending on parameters μ and σ . These findings illustrate an interesting interplay between rheological parameters, providing perspectives into the complicated behaviors of immiscible rotating fluids under different characteristics and useful implications for a variety of practical applications.

Investigating three-dimensional vortex evolution in centrifugal pump under rotating stall conditions using tomographic particle image velocimetry

A rotating stall in centrifugal pumps commonly occurs under off-design operations, which is a detrimental phenomenon leading to flow instabilities, pressure fluctuations, and reduced performance. A time-resolved non-intrusive three-dimensional (3D) flow visualization method is developed for investigating complex vortex structures in centrifugal pumps based on Omega vortex identification and tomographic particle image velocimetry (tomo-PIV). A special-made centrifugal pump prototype was developed with acrylic glass allowing for optical access. This method enables both qualitative and quantitative analysis of high spatiotemporal resolution on flow behaviors and dynamics under various stall conditions. The ultra-high sampling frequency realized over 40 time-consecutive observations per revolution under 0.2 Qd, 0.4 Qd, 0.6 Qd, and 0.8 Qd. It captures the instantaneous evolution of vortex structures that undergoes a growth–breakup transition within 7–9 ms. The rotating stall mechanism is revealed experimentally from the evolution of the vortex structure. Our analysis shows the tomo-PIV's additional velocity component aids in understanding the 3D characteristics of the stall. A substantial region of reverse flow in the z-axis direction is observed under 0.2 Qd. Vortex structures are more prone to blockage at the impeller inlet, exacerbating the stall phenomenon. As the flow rate increases, the velocity distributions across different layers exhibit a laminar characteristic with a more uniform profile. The vortex structures extend radially and migrate toward the outlet. The evolutions of the stall vortex, wake vortex, and inlet vortex share the same dominant frequency components (4.75fn and 5.25fn), but the flow rate affects the proportion of different frequency components.

Studying ion transport dynamics in electrochemical measurements of lateral flow assays

Lateral Flow Assays (LFAs) are among the most widely used biosensors. Conventional colorimetric LFAs yield binary, non-quantifiable results. Electrochemical LFAs (eLFAs) aim to overcome this limitation. However, the reported disadvantage of extreme sensitivity to experimental conditions poses a significant challenge in the development of new eLFAs. In this work, impedimetric measurements were performed to probe the impact of experimental factors such as electrolyte conductivity/ionic strength on the eLFA outcomes. The time-dependent evolution of non-Faradaic impedance measurements coupled with flow velocity computations were employed to investigate ion transport across different LFA configurations and buffer compositions. The analysis of the Péclet number, a characteristic dimensionless parameter of flow dynamics within the LFA, revealed the coexistence of diffusive and convective ionic transport regimes over the LFA operational time. In addition, our findings underscore the critical role of absorbent pad dead volume adjustments in governing the capacity to maintain sample flow within the membrane over extended durations. These electro-fluidics phenomena are essential considerations for conducting electrochemical measurements within LFAs. Overall, this study offers insights into key design parameters for the integration of electrochemistry into LFAs.

Richtmyer–Meshkov instability at high Mach number: Non-Newtonian effects

The Richtmyer–Meshkov instability (RMI) occurs when a shock wave passes through an interface between fluids of different densities, a phenomenon prevalent in a variety of scenarios including supersonic combustion, supernovae, and inertial confinement fusion. In the most advanced current numerical modeling of RMI, a multitude of secondary physical phenomena are typically neglected that may crucially change in silico predictions. In this study, we investigate the effects of shear-thinning behavior of a fluid on the RMI at negative Atwood numbers via numerical simulations. A parametric study is carried out over a wide range of Atwood and Mach numbers that probes the flow dynamics following the impact on the interface of the initial shock wave and subsequent, reflected shocks. We demonstrate agreement between our numerical results and analytical predictions, which are valid during the early stages of the flow, and examine the effect of the system parameters on the vorticity distribution near the interface. We also carry out an analysis of the rate of vorticity production and dissipation budget which pinpoints the physical mechanisms leading to instability due to the initial and reflected shocks. Our findings indicate that the shear-thinning effects have a significant impact on instability growth and the development of secondary instabilities, which manifest themselves through the formation of Kelvin–Helmholtz waves. Specifically, we demonstrate that these effects influence vorticity generation and damping, which, in turn, affect the RMI growth. These insights have important implications for a range of applications, including inertial confinement fusion and bubble collapse within non-Newtonian materials.

Numerical investigations on film cooling effectiveness and heat transfer performance of inclined film hole on the turbine blade squealer tip with plasma actuation

The turbine blade tip frequently encounters elevated thermal loads, necessitating effective protection measures. Conventional film cooling techniques, while employed to mitigate erosion, face challenges in achieving optimal performance due to intricate tip leakage flow dynamics. Thus, the development of advanced film cooling methodologies becomes imperative to ensure the optimal operation of blade tips. In this study, a novel film cooling approach is proposed, leveraging a combination of dielectric barrier discharge (DBD) plasma actuators and inclined film holes. This strategy aims to direct cooling jets towards the tip wall surface, enhancing film cooling efficacy on highly-loaded turbine squealer tips. Numerical investigations are conducted to assess film cooling effectiveness, heat transfer coefficients, and coolant jet flow characteristics across varying actuation strengths (0, 0.6, 0.8, and 1.0) by integrating plasma actuation forces into the Reynolds-Averaged Navier-Stokes equations. Additionally, the impact of different blow ratios (0.5, 1.0, and 1.5) on plasma flow control is examined. Results demonstrate that plasma actuation improves film cooling performance and effectively mitigates tip heat transfer, even in the presence of interfering tip leakage flow. Specifically, at an actuation strength of 1.0, the average blade tip film cooling effectiveness increases by 7.1%, accompanied by a 12.3% reduction in average heat transfer coefficient compared to scenarios without plasma actuation. Furthermore, the blow ratio influences plasma actuation performance, with minimal disparity observed between configurations with and without plasma devices under extreme blow ratio conditions.

Numerical Analysis of Film Cooling Flow Dynamics and Thermodynamics for Perfect and Imperfect Cooling Holes

Numerical Analysis of Film Cooling Flow Dynamics and Thermodynamics for Perfect and Imperfect Cooling Holes

Neuro-oncologic Emergencies.

Neuro-oncologic emergencies have become more frequent as cancer remains one of the leading causes of death in the United States, second only to heart disease. This article highlights key aspects of epidemiology, diagnosis, and management of acute neurologic complications in primary central nervous system malignancies and systemic cancer, following three thematic classifications: (1) complications that are anatomically or intrinsically tumor-related, (2) complications that are tumor-mediated, and (3) complications that are treatment-related. The main driver of mortality in patients with brain metastasis is systemic disease progression; however, intracranial hypertension, treatment-resistant seizures, and overall decline due to increased intracranial burden of disease are the main factors underlying neurologic-related deaths. Advances in the understanding of tumor-specific characteristics can better inform risk stratification of neurologic complications. Following standardized grading and management algorithms for neurotoxic syndromes related to newer immunologic therapies is paramount to achieving favorable outcomes. Neuro-oncologic emergencies span the boundaries of subspecialties in neurology and require a broad understanding of neuroimmunology, neuronal hyperexcitability, CSF flow dynamics, intracranial compliance, and neuroanatomy.

Step-by-step venous navigation in treatment of tentorial dural arteriovenous fistula supplied by artery of Bernasconi and Cassinari.

The artery of Bernasconi and Cassinari is a small infraclinoid branch of the internal carotid artery that originates from its cavernous segment and then runs along the tentorium. Because of its gracile appearance, it is often visible only when related to neoplasms and vascular lesions in the tentorial regions.1 Dural arteriovenous fistulas (dAVFs) are arteriovenous shunts contained within the dural leaflets, supplied largely by the regional meningeal arteries and classified based on the type of venous drainage. Tentorial dAVFs are mostly supplied by branches of the meningohypophyseal trunk, including the artery of Bernasconi and Cassinari.2 Unlike fistulas of other locations, tentorial fistulas are linked with a higher risk for venous hypertension and hemorrhage and thus demand immediate and appropriate treatment.3 Digital subtraction angiography is necessary to understand its arterial and venous components. Treatment aims to achieve complete embolization of the fistulous connection and venous portions by either a transarterial or transvenous approach, without causing serious changes in the flow dynamics.4, 5.

Influence of periodicity on natural convection in a square porous cavity due to non-uniform heat under LTNE state

In this article, the influence of the local thermal non-equilibrium (LTNE) state on free convection in a square cavity filled with fluid-saturated porous medium is investigated numerically. The steady-state flow is induced due to sinusoidal heat distributed on the side walls of the cavity and insulated of the horizontal walls. The coupled flow governing equations are solved numerically by using the finite volume method (FVM) consisting of the SIMPLER (Semi-Implicit Method for Pressure Linked Equation Revised) Algorithm. The numerical simulations of temperature and stream-function contours are carried out for the non-Darcy model. The developed code is validated with existing numerical and present computed results for the case of a square enclosure associated with non-uniform heat source. Then, the present numerical results are analyzed over a range of physical parameters, like periodicity parameter ( N ≥ 1 ), interface heat transfer coefficient ( 10 − 2 ≤ H ≤ 10 2 ), porosity scaled thermal conductivity ratio ( 10 − 2 ≤ γ ≤ 10 2 ), with a fixed Rayleigh number ( Ra = 10 6 ), Darcy number ( Da = 10 − 4 ), Prandtl number (Pr = 0.71), and porosity ( ε = 0.8 ). To study the impacts of these key parameters on the fluid flow behavior and isotherm patterns of fluid as well as solid phase in the porous-square enclosure. From present numerical experiments that the structure of flow is controlled by multicellular structure with rotating clockwise and anticlockwise directions in the entire results. The flow dynamics are highly affected by the periodicity parameter (N) under LTNE circumstances. The characteristics of the local Nusselt number have the point of inflection and the maximum magnitude of it increases with N. The significant effect of H is found on the heat transfer rate of fluid phase but it is negligible on the heat transfer rate of solid phase. However, the influence of γ is found reverse in nature on the heat transfer rate of fluid as well as solid phase when as compared to the effect of H.

Artificial neural computing and statistical analysis of heat and mass transport of nanofluid flow with melting heat and thermal stratification

The melting heat phenomenon in viscous nanofluid MHD flow over a stretching sheet with variable porosity and permeability was utilized. The behavior of magneto-viscous nanofluid flow was scrutinized using the concepts of machine learning and statistics. Thermal stratification, heat source, and activation energy in the solution of tween-20 nanoparticles and an ethyl-acetate base-type fluid are examined. Brownian and thermophoretic phenomena are included. Non-linear partial differential equations (PDEs) are converted into non-linear ordinary differential equations (ODEs) via von Karman similarity variables. Dataset is generated by the 4th-order Runge-Kutta numerical method for the artificial neural network. The ratio parameter and melting parameter enhance the velocity outline, while the melting parameter and thermal stratification parameter reduce the temperature outline. An increase in the concentration outline is seen with the activation energy parameter and Brownian motion parameter both increase the concentration outline. The system's performance using metrics like regression analysis, mean squared error, and error histograms is evaluated. The impact of these factors on significant results, such as the drag coefficient and heat transfer rate, is statistically investigated using multiple linear regressions. The integration of statistical and machine learning methods is deemed crucial for enhancing understanding of complex fluid dynamics in magnetic nanofluid flows.

Nature-Inspired Wind Farm Layout Optimization: Harnessing Smart Patterns for Sustainable Energy

This research investigates the transformative realm of wind farm layout optimization, with a specific focus on harnessing the efficiency of bio-inspired patterns. The positioning of wind turbine is play a vital role in the maximizing the energy output of a wind farm. If a wind turbine is placed in the wake region of the upstream turbine, the energy produced by the downstream turbine is reduced. Hence, it is imperative to place turbines in such a way that effect of the wake is minimum on a performance of turbines. The conventional grid-based approaches, commonly employed in wind farm layouts, face limitations in capturing the inherent complexity of wind flow dynamics, especially in varied terrains. In contrast, bio-inspired layouts, inspired by patterns observed in natural ecosystem, offer the promising results over the conventional Grid based approach. Our investigation involves the development and implementation of a novel bio-inspired wind farm layout positioning pattern. In the proposed approach, various nature inspired pattern like honeycomb and sunflower seeds pattern is explored for the turbine positioning. Further, the modeling of wind behavior includes both uniform wind speeds and variable wind speeds originating from all directions. The modified passing vehicle search (mPVS) optimization algorithm is used for optimizing the wind turbine placement. The results are obtained for the different wind scenario and compare it with the available results in the literature. The anticipated outcomes of this research include a deeper understanding of the potential benefits and challenges associated with bio-inspired wind farm layouts. The findings aim to contribute valuable insights into optimizing wind turbine placements, maximizing energy capture, and fostering sustainable practices in the wind energy sector. Results shows that the turbine positioning in the proposed bio-inspired pattern produce the higher power output (6%) compared to the conventional grid based approach. Hence, it can be concluded that the approach present in this study can assist wind farm designers and developers in optimally placing turbines for better performance.

Improving flow dynamics and storage longevity of a low-cost phosphorescent fingerprint powder.

An inexpensive, commercially available doped strontium aluminate phosphor with long-lived afterglow was prepared as a luminescent fingerprint dusting powder suited for challenging, highly patterned substrates; however, prolonged exposure to humidity was found to reduce that powder's affinity for fingermarks. Here, an enhanced preparation for synthesizing that fingerprint dusting powder is presented that prevents powder aggregation and loss of function upon exposure to humid environments. This was achieved by introducing a flow regulator during synthesis: hydrophobic silica SIPERNAT® D10 or SIPERNAT® D17. Increasing the hydrophobicity of the powder prevents aggregation by inhibiting the uptake of water, thereby improving the material's flow dynamics and transfer behavior from brush to fingermark. The angle of repose and flow characteristics made by the modified powders were quantified, with excellent affinity for fingermarks observed, even after being stored under 85% (±5%) humidity for 4 weeks. A preliminary comparison of the performance of the modified hydrophobic powders relative to the unmodified precursor revealed that more of the SIPERNAT® treated powder typically adhered to fingermarks while simultaneously imparting less background development. In addition, fewer clumps of particulate were observed in the developed fingermarks after addition of a hydrophobic flow regulator. This technical report outlines the updated method for synthesizing the fingerprint powder, with summarized flow performance results, and a demonstration of the modified powder's affinity for simulated fingermark evidence.