Flow Deceleration Research Articles

Two-phase flows downstream, upstream and within Plate Heat Exchangers

Air-water flows were assessed within Plate Heat Exchangers (PHE) with the aid of fast camera imaging. Tests occurred in transparent setups with three chevron angle arrangements (30o/30o, 30o/60o and 60o/60o), representative of low, in-between and high pressure drop channels. Evaluation upstream the PHE inlet happened with Electrical Capacitance Tomography. Three patterns were tested: bubbly, slug and stratified. The effects of flow direction, superficial fluid velocities, two-phase pattern, and chevron angle arrangement on air-water distributions were assessed. The PHE channel outlet is characterized by intense flow recirculation. Bubble entrapment occurs in the core of the recirculation zones. Energy dissipation processes along the PHE channel flow affect the inlet gaseous content, intensifying the mixing process of air and water phases, particularly at flow distribution areas owing to the occurrence of flow acceleration and deceleration. Bubble distribution is wide since the break-up process is rather heterogeneous. Prediction of the maximum bubble diameter was obtained with a modification to Hinze's model. Coalescence can occur with small liquid superficial velocities. At the exit manifold, the recirculation zones affect the two-phase pipe flow. In addition to swirling decay, two-phase flow features and gravitational forces need to be accounted to determine the necessary pipe length to attain stationary process.

Listening to heart sounds through the pressure waveform.

Non-invasive diagnostic modalities are integral to cardiovascular care; however, current systems primarily measure peripheral pressure, limiting the breadth of cardiovascular prognostication. We report a novel approach for extracting left side heart sounds using a brachial cuff device. The technique leverages brachial cuff device enhanced signal resolution to capture pressure fluctuations generated by cardiohemic system vibrations, the sound pressure waveform. We analyze left heart catheterization data alongside simultaneous brachial cuff device measurements to correlate sound pressure waveform features with left ventricle (LV) contractility. The extracted sound pressure waveform reveals two prominent oscillatory wave packets, termed WP1 and WP2, originating from cardiac structure vibrations associated with LV contractions and relaxation. We demonstrate that WP1 originates from LV contraction during systolic blood ejection through the aortic valve (AV) and is correlated with LV isovolumetric contraction, clinically measured by LV dPdt-max (Pearson-R = 0.65, p < 0.001). Additionally, we show that WP2 comes from LV elongation required for blood flow deceleration at the end of systole, causing AV closure, and is correlated with LV isovolumetric relaxation, measured by LV ndPdt-max (Pearson-R = 0.55, p < 0.001). These findings highlight the value of cuff sound pressure waveforms in providing insights about dynamic coupling of the LV-Aorta complex for non-invasive assessment of LV contractility.

A model-based quantification of nonlinear expiratory resistance in Plethysmographic data of COPD patients.

BackgroundChronic obstructive pulmonary disease (COPD) is characterised by airway obstruction with an increase in airway resistance (R) to airflow in the lungs. An extreme case of expiratory airway resistance is expiratory flow limitation, a common feature of severe COPD. Current analyses quantify expiratory R with linear model-based methods, which do not capture non-linearity's noted in COPD literature. This analysis utilises a simple nonlinear model to describe patient-specific nonlinear expiratory resistance dynamics typical of COPD and assesses its ability to both fit measured data and also to discriminate between severity levels of COPD. MethodsPlethysmographic data, including alveolar pressure and airway flow, was collected from n=100 subjects (40 healthy, 60 COPD) in a previous study. Healthy cohorts included Young (20-32 years) and Elderly (64-85 years) patients. COPD patients were divided into those with expiratory flow limitation (FL) and those without (NFL). Inspiratory R was treated as linear (R1,insp). Expiratory R was modelled with two separate models for a comparison: linear with constant resistance (R1,exp), and nonlinear time-varying resistance (R2,exp(t)) using b-splines. ResultsModel fit to PQ loops show inspiration is typically linear. Linear R1,exp captured expiratory dynamics in healthy cohorts (RMSE 0.3 [0.2 - 0.4] cmH2O), but did not capture nonlinearity in COPD patients. COPD cohorts showed PQ-loop ballooning during expiration, which was better captured by non-linear R2,exp(t) (RMSE 1.7[1.3-2.8] vs. 0.3[0.2-0.4] cmH2O in FL patients). Airway resistance is higher in COPD than healthy cohorts (mean R2,exp(t) for Young (1.9 [1.6-2.8]), Elderly (2.4 [1.4-3.5]), NFL (4.9 [3.9-6.6]) and FL (13.5 [10.4-21.9]) cmH2O/L/s, with p ≤ 0.0001 between aggregated measures for Young and Elderly healthy subjects and NFL and FL COPD subjects). FL patients showed non-linear R2,exp(t) dynamics during flow deceleration, differentiating them from NFL COPD patients. ConclusionsLinear model metrics describe expiration dynamics well in healthy subjects, but fail to capture nonlinear dynamics in COPD patients. Overall, the model-based method presented shows promise in detecting expiratory flow limitation, as well as describing different dynamics in healthy, COPD, and FL COPD patients. This method may thus be clinically useful in the diagnosis or monitoring of COPD patients using Plethysmography data, without the need for additional expiratory flow limitation confirmation procedures.

A Simulation Study of Low-power Relativistic Jets: Flow Dynamics and Radio Morphology of FR-I Jets

Radio galaxies are classified into two primary categories based on their morphology: center-brightened FR-I and edge-brightened FR-II. It is believed that the jet power and interactions with the ambient medium govern the deceleration and decollimation of the jet-spine flows, which, in turn, influence this dichotomy. Using high-resolution, three-dimensional relativistic hydrodynamic simulations, we follow the development of flow structures on sub-kiloparsec to kiloparsec scales in kinetically dominant low-power relativistic jets. We find that the bulk Lorentz factor of the jet spine and the advance speed of the jet head, which depend on the energy injection flux and the jet-to-background density contrast, primarily determine the dynamics and structures of the jet-induced flows. The entrainment of ambient gas and the background density and pressure gradient may also play significant roles. To emulate radio morphology, we produce the synthetic maps of the synchrotron surface brightness for the simulated jets, by employing simple models for magnetic field distribution and nonthermal electron population and considering relativistic beaming effects at different inclination angles. Both the flow structures and radio maps capture the longitudinal and transverse structures of the jet-spine and shear layer, consistent with observations. We also compare different background effects and argue that the loss of pressure confinement beyond the galactic core may be a key factor in the flaring and disruption of FR-I jets. Our results confirm that mildly relativistic jets could explain the one-sidedness or asymmetries with the boosted main jet and deboosted counterjet pairs.

Distribution of transitional flow deposits in sedimentary environments of mixed sand-mud turbidite system

Predicting facies distribution in turbidite systems is essential for resource exploration and identifying geohazards from an economic standpoint. Models that describe facies distribution depend heavily on understanding the mechanisms of particle transport and deposition. These processes are closely tied to the volume, concentration, and composition of sediment gravity flows, which display a range of behaviours between turbulent and laminar flow extremes. Recently, there has been a rise in studies on transitional flow deposits, although they remain much less understood than fully turbulent or laminar flows.For the first time, the distribution of Structured sandstone–mudstone associated with transitional flow deposits has been quantitatively presented for various sedimentary environments within the turbidite system. The distribution of Structured sandstone–mudstone was analysed for six areas of the Ropianka Fm (Skole Nappe, Polish Outer Carpathians) across twelve sedimentary environments, including channels, channel-levees, channel-mouths, and sub-environments of the depositional lobe. An increased amount of Structured sandstone–mudstone was observed in proximal settings away from the transport axis and in the distal parts of the turbidite system. It was found that flow transformation can occur in both proximal and distal zones of the turbidite system. Structured sandstone–mudstone in proximal zones is more often deposited from diluted mud-laden flows of small volume, where fine-grained cohesive material likely underwent vertical segregation. In contrast, Structured sandstone–mudstone formed basinward tend to be initially formed by larger flows. In proximal part of depositional lobe setting, the flow transformation due to longitudinal or longitudinal and vertical segregation of fine-grained cohesive material occurs slowly. At this point the velocity of sediment gravity flow is too high and the concentration of cohesive particles is too low for common development of cohesive bonds. Flow transformation accelerates in lobe fringe and lobe distal fringe/interlobe, due to flow deceleration, changes in sand-to-mud ratio, and the time required for development of cohesive bonds and the transition to a transitional flow regime, leading to increased deposition of Structured sandstone–mudstone distally.

Novel clinical method: left ventricular diastolic pressure curve by echocardiography

Abstract Background A non-invasive clinical method for construction of the systolic part of the left ventricular (LV) pressure curve was recently introduced. There is, however, no clinical method available to construct the LV diastolic pressure curve. Purpose The aim of this study was construction of patient-specific LV diastolic pressure curves from echocardiographic data and have initial validation against simultaneously acquired pressure curves by high-fidelity LV pressure catheters (micromanometers). Methods The study included 108 patients referred for diagnostic left heart catheterization due to suspected coronary artery disease. 81 patients were used as a training cohort. The construction of a diastolic pressure curve is based on a reference unitless pressure trace and seven key pressure-time diastolic events estimated in each patient. The reference diastolic pressure trace was generated from a group of 8 patients with LV pressures recorded by micromanometer. Each individual pressure trace from the reference cohort was first annotated with the occurrence of the key diastolic events: mitral valve (MV) opening, minimum LV pressure, peak of early-diastolic mitral flow velocity (E) and start and peak of atrial contraction-induced velocity (A), and MV closure. Then the temporal intervals between these events were normalized before calculating an averaged pressure curve (Figure 1, panels A-C). A patient-specific LV diastolic pressure curve was constructed by adjusting the standard curve according to estimated LV pressure at the key diastolic events (shown in Figure 1D). The estimation of the pressure-time instants is based on the LV volume temporal transient, used to estimate filling flow rate (Q=dV/dt) and flow acceleration and deceleration (dQ/dt=d2V/dt2), as well as a set of biomarkers including left atrial reservoir strain, peak systolic LV pressure, and body mass index. LV volume temporal traces were generated by combining global 2D volumes with global longitudinal strain. The ability to generate patient-specific diastolic LV pressure curves was validated in a second cohort of 7 patients studied with micromanometer-tipped catheters. Echocardiography and LV pressure were recorded from the same series of beats and recordings were done during breath-hold at end-expiration. The agreement was accessed qualitatively and considering the mean diastolic LV pressure. Results There was good agreement between measured and estimated LV diastolic pressure curves, qualitatively and quantitatively, via mean diastolic PLV: Bias 0.2 mmHg, limits of agreement &amp;lt;3.2 mmHg (Figure 1D-F). Conclusions The results suggest that the LV diastolic pressure curve can be estimated by echocardiography. The method needs validation in larger populations.Non-invasive diastolic LV pressure curve

Non-invasive assessment of left ventricular hemodynamic forces in hypertrophic cardiomyopathy

Abstract Background Hemodynamic force (HDF) analysis allows non-invasive measurement of intraventricular pressure gradients, portraying cyclic spatial-temporal interaction between blood and tissues. Impaired HDFs have been implicated in early detecting of adverse cardiac remodelling and treatment response in various cardiovascular disorders, providing insights into cardiac physiology not offered by traditional cardiovascular imaging (1). Mainly explored in heart failure, HDF analysis has not been previously applied to hypertrophic cardiomyopathy (HCM). Purpose To investigate differences in systo-diastolic function in HCM patients compared to healthy controls using HDF analysis. Methods Forty patients with HCM diagnosis (20 obstructive and 20 non-obstructive) were retrospectively evaluated in comparison with 22 healthy controls. Left ventricular (LV) HDFs were derived from routine transthoracic apical 4-, 2- and 3-chamber views using a dedicated software. Apical-basal HDF curves were generated, where positive deflections represent forces directed from the LV apex to the base, whilst negative ones are directed toward the apex. Amplitude and timing parameters were derived, the latter indexed to total cardiac cycle duration. Results Table 1 shows the demographic, clinical and echocardiographic characteristics of HCM compared to controls. Patients with HCM were older, had a slower heart rate due to treatment with beta-blockers, and showed hypercontractility, as expressed by higher LV ejection fraction. Compared to controls, HCM patients showed reduced LV longitudinal force, i.e. the force during the whole cardiac cycle (4.17% [2.36-5.52] vs. 6.01% [4.73-7.78], p=0.002), shorter time interval to systolic peak (0.15 [0.12-0.16] vs. 0.19 [0.17-0.20], p &amp;lt;0.001), and shorter duration of LV impulse (0.29 [0.27-0.32] vs. 0.34 [0.32-0.37], p &amp;lt;0.001) (Figure 1). However, no differences in terms of systolic force peak (p=0.283) or LV impulse intensity (p=0.689) were detected. During the transition between systole and diastole, LV suction (i.e. the interval including late systolic deceleration and early diastolic suction) was significantly longer (0.26 [0.22-0.29] vs. 0.23 [0.21-0.25], p=0.023) but less pronounced (6.30% [4.56-8.44] vs. 8.72% [6.71-12.59], p=0.005), likely reflecting a relaxation impairment from the very beginning of diastole. Such impairment was maintained during early diastolic filling, where the amplitude of the positive deceleration flow force was severely reduced in HCM compared to controls (2.98% [1.98-4.58] vs. 7.11% [4.55-8.72], p &amp;lt;0.001). Conclusions HDF analysis in HCM patients revealed unique systolic and diastolic changes reflecting faster LV contraction during systole and slower and weaker LV forces during diastole. This analysis deepens our understanding of HCM mechanic abnormalities and may help assess response to innovative treatment options.

Development and testing of a measuring chamber for a device for express analysis of milk quality in a flow

Mechanization and robotization of dairy farms require the development of technologies for assessing the quality of manufactured products. Monitoring milk composition and milking duration in real time is especially important for prompt response to deviations in animal physiological state parameters and timely adjustment of rations when milk yields decrease. The first version of the scatterometric device for express analysis of milk quality used a glass measuring chamber with a simple round cross-section, but it did not ensure the reduction of the turbulent flow of the milk-air mixture to laminar. This study presents the development and testing of a prototype of a measuring chamber that provides deceleration and laminarization of the milk-air mixture flow. The device operates at a milking capacity of 1 to 6 l/min, flow speed from 0.2 to 1.8 m/s. In the developed measuring chamber, a special bypass is created at an angle of 45° so that it has a common slot with the main tube. In this bypass, the flow of the milk-air mixture is slowed down to reduce turbulence and the number of air bubbles that interfere with the operation of scatterometric devices. The measurement area of the device is located in the upper part of the bypass. As a result, the developed measuring chamber has an internal diameter of the main part of 15 mm, the bypass of 11 mm, and provides close to 100% filling of the branch with liquid at the moment of the milk plug passage. The developed measuring chamber allowed the new version of the express milk quality analysis device to achieve increased accuracy and stability of measurements.

The Role of Fluvial Morphodynamic Hierarchy in Shaping Bedform Deposits

AbstractFluvial cross strata are fundamental sedimentary structures that record past flow and sediment transport conditions. Bedform preservation can be significantly influenced by the presence of larger‐scale topographic features that cause spatial gradients in flow. However, our understanding of the controls on cross strata preservation in the presence of a morphodynamic hierarchy is limited. Here, using high‐resolution bathymetry from a physical experiment, we quantify bedform evolution and cross strata preservation in a zone of flow expansion and deceleration. Results show that the size and celerity of superimposed bedforms decreases along the host‐bedform lee slope, leading to a systematic downstream increase in the sediment accumulation rate relative to bedform celerity. This increase in local bedform climb angle results in the preservation of a larger fraction of formative bedforms. Our results highlight the need to revise current paleohydraulic reconstruction models, and demonstrates that fluvial morphodynamic hierarchy is a fundamental determinant of sedimentary strata.

Abyssal Slope Currents

Abstract Realistic computational simulations in different oceanic basins reveal prevalent prograde mean flows (in the direction of topographic Rossby wave propagation along isobaths; a.k.a. topostrophy) on topographic slopes in the deep ocean, consistent with the barotropic theory of eddy-driven mean flows. Attention is focused on the Western Mediterranean Sea with strong currents and steep topography. These prograde mean currents induce an opposing bottom drag stress and thus a turbulent boundary-layer mean flow in the downhill direction, evidenced by a near-bottom negative mean vertical velocity. The slope-normal profile of diapycnal buoyancy mixing results in down-slope mean advection near the bottom (a tendency to locally increase the mean buoyancy) and up-slope buoyancy mixing (a tendency to decrease buoyancy) with associated buoyancy fluxes across the mean isopycnal surfaces (diapycnal downwelling). In the upper part of the boundary layer and nearby interior, the diapycnal turbulent buoyancy flux divergence reverses sign (diapycnal upwelling), with upward Eulerian mean buoyancy advection across isopycnal surfaces. These near-slope tendencies abate with further distance from the boundary. An along-isobath mean momentum balance shows an advective acceleration and a bottom-drag retardation of the prograde flow. The eddy buoyancy advection is significant near the slope, and the associated eddy potential energy conversion is negative, consistent with mean vertical shear flow generation for the eddies. This cross-isobath flow structure differs from previous proposals, and a new one-dimensional model is constructed for a topostrophic, stratified, slope bottom boundary layer. The broader issue of the return pathways of the global thermohaline circulation remains open, but the abyssal slope region is likely to play a dominant role.

Characterizing magnetohydrodynamic effects on developed nanofluid flow in an obstructed vertical duct under constant pressure gradient

Abstract This research endeavors to conduct an examination of the thermal characteristics within the duct filled with the copper nanoparticles and water as base fluid. In exhaust systems, like car exhausts, chimneys, and kitchen hoods, duct flows are crucial. These systems safely discharge odors, smoke, and contaminants into the atmosphere after removing them from enclosed places. The study focuses on a laminar flow regime that is both hydrodynamically and thermally developed, with a specified constraints at any cross-sectional plane. To address this, we employ the finite volume method as it stands as a judicious choice, offering a balance between computational efficiency and solution accuracy. Notably, we have observed that the deceleration of flow induced by elevated Rayleigh numbers can be effectively regulated by the application of an appropriately calibrated external magnetic field. The prime parameters of the problem with ranges are: pressure gradient ( 1 ≤ p 0 ≤ 100 ) (1\le {p}_{0}\le 100) , Hartmann number ( 0 ≤ Ha ≤ 50 ) (0\le \text{Ha}\le 50) , Rayleigh number ( 1 , 000 ≤ Ra ≤ 40 , 000 ) (1,000\le \text{Ra}\le 40,000) , and magnetic parameter ( 0 ≤ M ≤ 50 ) (0\le M\le 50) . Furthermore, our analysis reveals that the Nusselt number exhibits a nearly linear correlation with the nanoparticle volume fraction parameter, a trend observed across a range of Rayleigh numbers and magnetic parameter values. We have noted that a mere 20% nanoparticle volume fraction can result in up to 62% rise in the Nusselt number while causing an almost 50% decrease in the factor f Re. This research framework serves as a robust foundation for understanding the intricate interplay between magnetic influences and thermal-hydraulic behavior within the delineated system.

Unified framework for laser-induced transient bubble dynamics within microchannels

Oscillatory flow in confined spaces is central to understanding physiological flows and rational design of synthetic periodic-actuation based micromachines. Using theory and experiments on oscillating flows generated through a laser-induced cavitation bubble, we associate the dynamic bubble size (fluid velocity) and bubble lifetime to the laser energy supplied—a control parameter in experiments. Employing different channel cross-section shapes, sizes and lengths, we demonstrate the characteristic scales for velocity, time and energy to depend solely on the channel geometry. Contrary to the generally assumed absence of instability in low Reynolds number flows (<1000\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$<1000$$\\end{document}), we report a momentary flow distortion that originates due to the boundary layer separation near channel walls during flow deceleration. The emergence of distorted laminar states is characterized using two stages. First the conditions for the onset of instabilities is analyzed using the Reynolds number and Womersley number for oscillating flows. Second the growth and the ability of an instability to prevail is analyzed using the convective time scale of the flow. Our findings inform rational design of microsystems leveraging pulsatile flows via cavitation-powered microactuation.

Wall Modeling of Turbulent Flows with Varying Pressure Gradients Using Multi-Agent Reinforcement Learning

We propose a framework for developing wall models for large-eddy simulation that is able to capture pressure-gradient effects using multi-agent reinforcement learning. Within this framework, the distributed reinforcement learning agents receive off-wall environmental states, including pressure gradient and turbulence strain rate, ensuring adaptability to a wide range of flows characterized by pressure-gradient effects and separations. Based on these states, the agents determine an action to adjust the wall eddy viscosity and, consequently, the wall-shear stress. The model training is in situ with wall-modeled large-eddy simulation grid resolutions and does not rely on the instantaneous velocity fields from high-fidelity simulations. Throughout the training, the agents compute rewards from the relative error in the estimated wall-shear stress, which allows them to refine an optimal control policy that minimizes prediction errors. Employing this framework, wall models are trained for two distinct subgrid-scale models using low-Reynolds-number flow over periodic hills. These models are validated through simulations of flows over periodic hills at higher Reynolds numbers and flows over the Boeing Gaussian bump. The developed wall models successfully capture the acceleration and deceleration of wall-bounded turbulent flows under pressure gradients and outperform the equilibrium wall model in predicting skin friction.

Nonlinear time-dependent behavior of rheodictic polymers: A theoretical and experimental investigation

The present study examined the nonlinear time-dependent behavior of rheodictic polymers, a class of noncrosslinked materials that exhibit flow. Such behavior was addressed with extended Schapery's nonlinear viscoelastic model by introducing new physical quantities, i.e., the flow term Φflow and corresponding nonlinear shift parameter g2,flow. While Φflow portrays irrecoverable deformation, g2,flow depicts a nonlinear contribution to flow acceleration. This theory was accompanied by analytical and experimental methodologies for identifying all the parameters in the linear and nonlinear viscoelastic domains. Predictions of long-term time-dependent behavior (in shear) at various stress states show excellent agreement with the experimental data, i.e., within 5% error, obtained for polycarbonate at 130°C. Surprisingly, the newly introduced g2,flow indicates that flow retardation occurs with increasing stress, implying that a highly deformed entangled system hinders molecular reptation/disentanglement. Nevertheless, the proposed extension of Schapery's nonlinear viscoelastic model not only allows accurate predictions of the nonlinear time-dependent behavior of rheodictic polymers but also enables a detailed outlook on the underlying molecular mechanisms under severe environmental and loading conditions.

Carbonate‐rich megabeds within a Triassic siliciclastic deep‐water system, West Qinling orogenic belt, Central China: Character, processes and implications

AbstractDeep‐water megabeds are a particular type of sediment gravity flow deposit that are anomalously thick and often of distinctive composition compared to the deep‐water strata within which they are embedded. Pure siliciclastic or carbonate megabeds have been widely reported from deep‐marine systems. Less documented are carbonate‐rich mixed megabeds with abundant carbonate clasts in a siliciclastic matrix, which are embedded in siliciclastic deep‐water systems. Here, such examples are reported from outcrops of the Lower Triassic in the West Qinling orogenic belt, central China, with a focus on the character, processes and implications of these carbonate‐rich megabeds. Based on regional geology and characteristics of the encasing siliciclastic turbidites and autochthonous micritic limestones, these megabeds are inferred to have been deposited in a deep marine trough. The megabeds are thick (1 to ca 10 m) compared to surrounding beds (commonly less than 1 m), and are of mixed composition, comprising both siliciclastic grains and shallow‐water carbonate clasts. These megabeds are commonly characterised by a distinctive bipartite or tripartite vertical succession of facies. A complete (tripartite) sequence consists of a basal clast‐supported conglomeratic division (Division I), an intermediate matrix‐supported conglomeratic division (Division II), and an upper normally graded and/or laminated sandy division (Division III). These divisions are interpreted to be deposited from evolving debris flows transitioning to turbidity currents during a single flow event, and are the result of flow deceleration and dilution. The megabeds show variability over very short lateral distances (several tens to a few hundred metres), possibly related to surface relief on the debritic portion of the deposit. A new depositional model is proposed for the mixed deep‐water system, with frequent siliciclastic turbidite deposition within this elongate basin from axially flowing turbidity currents, and episodic deposition from laterally‐supplied carbonate‐rich megaflows that eroded and incorporated the substrate during transport.

Spreading dynamics of a microgel particle-laden thermosensitive polymer drop along smooth and nanofiber surfaces

The research focuses on the influence of 300-μm microgel particles in an aqueous solution of a thermosensitive biopolymer on the spreading and deformation of 3.7-mm drops. The drops impact a smooth hydrophilic and a rough hydrophobic surface. A mass fraction of microgel particles varies in a range of 0–0.2. A universal physical model of the spreading of thermosensitive polymer drops laden with microgel particles along surfaces with significantly different roughness is proposed. It explains the strong inhomogeneity of the contact line stretching due to the deceleration of the continuous phase flow by microgel particles and the increased flow vorticity because of the addition of the surface roughness factor. The validity of the proposed physical model is proven by qualitative and quantitative assessments of the contact line deformation when spreading. An empirical expression for the maximum spreading factor is derived, taking into account the properties of liquids, wall roughness, and microgel particle concentration; it reliably predicts when Re≈110−3100, the surface roughness is 0.5–125 nm, Ca=4.5×10−7, and the number of microgel particles in drops is up to 100. The expression was successfully tested during the modeling of arbitrary surface roughness and the increased concentration of microgel particles relative to those considered in experiments during the formation of a biopolymer layer. When developing the method of additive manufacturing of a functional layer, a practical correlation was established between the volume content of microgel particles, acting as potential containers for living cells, in a drop and the area of the biopolymer layer.

Vegetation promotes flow retardation and retention in deltaic wetlands

AbstractWe introduce a new approach to observe the impact of vegetation on tidal flow retardation and retention at large spatial scales. Using radar interferometry and in situ water level gauge measurements during low tide, we find that vegetation in deltaic intertidal zones of the Wax Lake Delta, Louisiana, causes significant tidal distortion with both a delay (between 80 and 140 min) and amplitude reduction (~ 20 cm). The natural vegetation front delays the ebb tide, which increases the minimum water level and hydro‐period inside the deltaic islands, resulting in better conditions for wetland species colonizing low elevations. This positive feedback between vegetation and hydraulics demonstrates the self‐organization functionality of vegetation in the geomorphological evolution of deltas, which contributes to deltaic stability.

Development of Curved Shape Diffuser Duct for Aero Engines With a Backend Centrifugal Compressor

In the present study, a design of the curved shape diffuser-duct is proposed to apply to the compressor stage for aero-engines with a backend centrifugal compressor. For these configurations, the flow exiting radially from the centrifugal impeller needs to be changed from radial-to-axial direction to meet downstream combustion chamber requirements. Hence, the specially designed exit duct with a curved shape to manage the flow from the radial-to-axial direction was later diffused using the diffuser-shaped exit duct. This study aims to design and develop an efficient diffuser-duct for the adequate deceleration of flow in the exhaust diffuser and, as a result, a uniform and low-velocity flow at the exit. This configuration comprises a radial-to-axial turning annular passage at the centrifugal impeller exit. Then, the passage is directed to either a purely axial direction or is inclined to the axial direction by a slight angle. The results indicate a uniform total pressure at the stage exit with marginal variation along the span. It shows equivalent end wall effects near both the shroud and hub surfaces. This endwall effect may be occurring mainly due to the growth of the boundary layer across the diffuser passage.

Mathematical modeling of entropy generation in MHD mixed convective Cu–Ag-Al2O3/H2O tri-hybrid nanofluid over an exponential permeable shrinking surface with radiation and slip impacts: Multiple solutions with stability analysis

The present investigation aims to determine the existence of a dual solution in magnetohydrodynamic (MHD) mixed convective radiative flow of Cu-Ag- A l 2 O 3 / H 2 O tri-hybrid nanofluid in a permeable Darcy–Forchheimer porous medium over an exponentially shrinking surface by considering velocity, thermal slips, and suction effects at the surface. This study focuses on assessing entropy production in novel coolant applications. To streamline the analysis, the complex nonlinear partial differential equations (PDEs) are simplified by converting them into a set of ordinary differential equations (ODEs) through the utilization of the similarity transformation technique. These ODEs are then solved utilizing the bvp4c numerical MATLAB function. Graphical and tabular analyses are conducted to investigate the impact of emerging variables on entropy generation, as well as velocity, temperature, skin friction coefficient, and Nusselt number. Due to the contraction of the surface, dual solutions are found, but dual solutions cannot be found beyond the critical values. The critical values of S C are 1.58928, 1.48700, and 1.66058, but ξ C are − 1.239499 , − 1.416999 , and − 1.130030 for Cu / H 2 O nanofluid, Cu − Ag / H 2 O hybrid nanofluid, and Cu − Ag − A l 2 O 3 / H 2 O tri-hybrid nanofluid, respectively. A positive minimum eigenvalue γ 1 signifies the existence of the upper stable solution branch, while a negative minimal eigenvalue indicates the presence of the lower unstable solution branch. The tri-hybrid nanofluid exhibits superior thermal properties compared to nanofluid and hybrid fluids. Adding nanoparticles to traditional fluids is perceived as improving their ability to transmit heat. The analysis has demonstrated that the thermal radiation and temperature slip parameters significantly influence the heat transfer rate. Thermal radiation is found to speed up the creation of entropy. Additionally, in the case of a stable solution, an increase in the Forchheimer number results in a deceleration of the liquid flow, an effect which is further amplified by the presence of the magnetic field and velocity slip parameter.

On the low-frequency flapping motion in flow separation

Transitional separating flow induced by a rectangular plate subjected to uniform incoming flow at Reynolds number (based on the incoming velocity and half plate height) 2000 is investigated using direct numerical simulation. The objective is to unveil the long-lasting mystery of low-frequency flapping motion (FM) in flow separation. At a fixed streamwise-vertical plane or from the perspective of previous experimental studies using pointwise or planar measurements, FM manifests as a low-frequency periodic switching between low and high velocities covering the entire separation bubble. The results indicate that in three-dimensional space, FM reflects an intricate evolution of streamwise elongated streaky structures under the influence of separated shear layer and mean flow reversal. The FM is an absolute instability, and is initiated through a lift-up mechanism boosted by mean flow deceleration near the crest of the separating streamline. At this particular location, the shear bends the vortex filament abruptly, so that one end is vertically struck into the first half of the separation bubble, whereas the other end is extended in the streamwise direction in the second half of the separation bubble. These two ends of vortex filament are mutually sustained and also stretched by the vertical acceleration and streamwise acceleration in the first and second halves of the separation bubble, respectively. This process periodically switches the low-velocity (or high-velocity) streaky structure to a high-velocity (or low-velocity) streaky structure encompassing the entire separation bubble, and thus flaps the separated shear layer up and down in the vertical direction. A ‘large vortex’ shedding manifests when the streaky structure switches signs. This large vortex is fundamentally different from the spanwise vortex shedding residing in the shear layer originated from the Kelvin–Helmholtz instability and successive vortex amalgamation. It is also believed that the three-dimensional evolution of streaky structures in the form of FM is applicable for both geometry- and pressure-induced separating flows.