Weak Flow Research Articles

Acoustic Field Imaging of Pipeline Turbulence for Noninvasive and Distributed Gas Flow Measurement

Precise control and measurement of the flow are essential for pipeline safety monitoring and economic accounting. Nowadays, the measurement of pipeline flow relies on point measurement schemes such as mechanical flowmeters, which invade the pipeline and can irreversibly damage the fluid pressure, especially when multipoint measurements are required. To overcome these problems, we have explored a novel technique in which the acoustic field properties of pipeline turbulence are reflected by distributed backscattering light field, from which the flow can be measured via acoustic field imaging. The acoustic field information is recorded by a helical deployment scheme using backscattering-enhanced optical fiber (BEOF) encapsulated in the polyethylene anticorrosive layer, thereby achieving highly sensitive, noninvasive, and distributed online monitoring of gas flows. We obtained 24-h flow fluctuation distributions with only one sensing fiber for two operating gas pipelines, and the flow measurement accuracy reached higher than 98% within the error range of −15% to 15%. Moreover, the minimum detectable flow is evaluated and it is demonstrated that the proposed scheme is extremely sensitive to weak flows. We successfully demonstrated noninvasive and distributed online measurement of operational pipeline flow, which will exhibit great potential for pipeline integrity management in the future.

Direct Observation of Nanotracer Transport in Swarming Bacteria during Antibiotic Adaptation.

Microorganisms inevitably encounter environmental variations and thus need to develop necessary strategies to adjust the colonies for survival. Here, we use cooperating Serratia marcescens bacteria to reveal how the whole population responds to a gradually deteriorating habitat. When subjected to antibiotics with increasing doses, the swarming bacteria transform weak homogeneous turbulent flows to nematic jet flows with defects and vortices on a large scale, by which bacteria exploit these coherent flows to transfer material and/or information. We elucidate a complete view of detailed spatiotemporal transport behavior in such microscale active turbulence with single-nanoparticle tracking. The nanoparticles in these active flows are brought into the state with the up limit of superdiffusion by the bacterial collective response to the stronger antibiotic stimulation. Strikingly, we found that, under the strengthening stimulation from antibiotics, bacteria with only a small fraction of their community get elongated and facilitate the drastic turbulence transition and an enhanced superdiffusion. These findings imply a possible collective response mechanism against environmental variations.

The performance of equilibrium radial electric field shear on microturbulence with different magnetic shears in tokamak plasmas

Global gyrokinetic particle simulations show that equilibrium radial electric field (E r ) shear reduces the linear growth rate, ion heat conductivity, and nonlinear turbulence amplitude for both the ion temperature gradient (ITG) and kinetic ballooning mode (KBM) microturbulence by tilting the poloidal mode structure. The increase in the magnetic shear enhances the stabilizing performance of the E r shear on linear growth rate for the ITG case but has no effect on that for the KBM case. The radial correlation length of the ITG turbulence is decreased by increasing the magnetic shear in a weak ion diamagnetic flow shear condition with low β, leading to a reduction in the effective E × B shearing rate, which weakens the suppression performance of the E r shear on the ITG turbulence amplitude. In contrast, under a larger ion diamagnetic shear flow for higher β, an increase in magnetic shear strengthens the suppression performance of the E r shear on the KBM turbulence amplitude due to an increase in the effective shearing rate by increasing the radial correlation length of the turbulence.

Evaluation of the validity of mental foramen USG measurements by comparison with CBCT and determination of blood flow.

To examine mental foramen (MF) morphology and morphometry in comparison with ultrasonography (USG) and cone-beam computed tomography (CBCT), and to determine the relationship between mental artery blood flow parameters and age, gender, dental status, alveolar crest height, mandibular cortical index (MCI) with USG. A total of 120 MF and mental arteries of 60 patients (21 males and 39 females), including 20 patients in each group, aged 18-39, 40-59, and 60years and above, were evaluated. The horizontal and vertical diameter of the MF and the distance between it and the alveolar crest were evaluated with USG and CBCT. In addition, mental artery blood flow parameters were examined by USG. When the horizontal diameter values of MF were compared in USG and CBCT measurements; the diameter was significantly lower in the measurements obtained by USG (p < 0.05). It was observed that there were no mental arteries whose blood flow could not be recorded, 31 (25.8%) had strong blood flow and 89 (74.2%) had weak blood flow. No significant correlation was observed between gender and blood flow parameters (p > 0.05). Considering that CBCT images are used as gold standard in our study, it may be said that USG is not as reliable as CBCT in evaluating the MF dimensions in the maxillofacial region. Nevertheless, USG is a suitable technique for determining the visualizing and blood flow of the MF.

Morphological variability of the white carp (Hypophthalmichthys molitrix) during domestication

Acclimatized in the last century in the reservoirs of Russia, the white silver carp is the only consumer of phytoplankton in our country. In conditions of artificial reproduction and domestication, uncontrolled deterioration of fish habitus often occurs. In this regard, a comparative analysis of the variability of the most informative morphological parameters, namely length, mass, head length, body girth and their main indices in the samples of the white silver carp of varying degrees of domestication, was carried out. The Chinese, Amur and local lineages, the Ergenin sample and the Romanian population were studied, of which the least domesticated is the Chinese line. The presented materials show that the Chinese white carp line of the second generation of domestication differs in a smaller head, high indices of relative head length and physical development from the local and Ergeninsky fish samples domesticated for several decades. In pond lines domesticated in several generations, there is an increase in the relative size of the head and a deterioration in the index of physical development, which indicates the presence of selection for fitness to insufficient food supply in conditions of weak flow. It is recommended in the breeding program when growing reproductive herds of white carp in ponds to provide for selection to preserve the commercial qualities of fish.

Large eddy simulation of a row of impinging jets with upstream crossflow using the lattice Boltzmann method

Large eddy simulations of a row of seven jets emerging from a perforated pipe and impinging on a flat heated plate were carried out using a compressible hybrid thermal lattice Boltzmann solver. The average Reynolds number of the emerging jets was 5000, with an exit-to-plate distance of 3 jet diameters. Two levels of upstream crossflow were simulated: one with weak cross flow, with a velocity ratio of ≈9.7, and one with strong cross flow, with a velocity ratio of ≈2. The flow field and heat transfer statistics were validated against experimental PIV and infrared thermography data from a recent study, showing good agreement. The effect of varying the Mach number on the wall heat transfer was subsequently tested. It was found that an increased Mach number lead to an increased value of the Nusselt number near the stagnation points.

New insights into the extended and generalised PTT constitutive differential equations: weak flows

This work presents a comparison between the PTT-X (extended Phan-Thien and Tanner (PTT)) and the generalised PTT (gPTT) viscoelastic models. The PTT-X model was derived based on a combination of reptation and network theories, allowing in this way a microstructural justification for the kernel function. The gPTT model is based on the network theory, with an empirical kernel function for the rate of destruction of junctions, that proved to be effective fitting experimental rheological data for polymer melts and solutions. A review on the background of both models is provided and the two models are then compared considering simple flows. This comparison allows one to attribute in some way a microstructural nature to the parameters involved in the gPTT model. Also, a new analytical solution is derived for the Poiseuille flow of the PTT-X model.

Rezum: a novel transurethral water vapor therapy for benign prostatic hyperplasia

Rezum: a novel transurethral water vapor therapy for benign prostatic hyperplasia

Non-Brownian diffusion and chaotic rheology of autophoretic disks.

The dynamics of a two-dimensional autophoretic disk is quantified as a minimal model for the chaotic trajectories undertaken by active droplets. Via direct numerical simulations, we show that the mean-square displacement of the disk in a quiescent fluid is linear at long times. Surprisingly, however, this apparently diffusive behavior is non-Brownian, owing to strong cross correlations in the displacement tensor. The effect of a shear flow field on the chaotic motion of an autophoretic disk is examined. Here, the stresslet on the disk is chaotic for weak shear flows; a dilute suspension of such disks would exhibit a chaotic shear rheology. This chaotic rheology is quenched first into a periodic state and ultimately a steady state as the flow strength is increased.

A generalized theory of flow forcing by rough topography

An analytical model is developed which explores the impact of irregular sea-floor roughness on large-scale oceanic flows. The previously reported asymptotic ‘sandpaper’ theory of flow-topography interaction represents relatively swift currents and exhibits singular behaviour in the weak flow limit. The present investigation systematically spans a wider parameter space and identifies the principal dissimilarities in the topographic regulation of slow and fast currents. The fast flows are controlled by the Reynolds stresses produced by topographically generated eddies. In contrast, relatively weak flows are more affected by the eddy-induced bottom form drag. The asymptotic models for fast and slow currents are then combined to arrive at a concise description of flow forcing by small-scale topography in homogeneous and multilayer models. The proposed closure is validated by comparing corresponding topography-resolving and parametric simulations.

Physical Property Analysis and Sensitivity Damage Evaluation of Tight Sandstone Gas Reservoirs

Tight sandstone reservoirs are widely distributed in China, because tight reservoirs have the characteristics of low porosity and low permeability, high clay mineral content, etc., it is easy to cause reservoir damage during hydraulic fracturing and is not easy to recover. X-ray whole-rock diffraction analysis was carried out through tight sandstone reservoir core, and the proportion of sensitive minerals in tight sandstone gas reservoir was clarified, and water sensitivity and flow velocity sensitivity damage experiments were carried out based on the test results. The experimental results show that the flow velocity sensitivity damage rate of tight sandstone reservoir is 28.02%, and the critical flow rate is 0.75ml/min, which is a weak flow rate sensitivity injury. The water-sensitive injury rate was 63.98%, which was moderately strong water-sensitive injury.

Swimming of Buoyant Bacteria in Quiescent Medium and Shear Flows.

Gravity has an unavoidable effect on all living organisms inhabiting fluidic surroundings. To investigate the spatial distribution of bacteria in quiescent fluids and their rheotactic behavior in shear flows under buoyancy, we adjust the buoyant force to regulate bacterial swimming in a microfluidic channel. It is found that swimming bacteria of Escherichia coli exhibit an obvious vertical separation when exposed to a medium with high density and gradually gather close to the up wall within minutes. The bacterial population presents a net upward number flux, which enhances the trapping of motile bacteria onto the up surface as a result of buoyancy force apart from the hydrodynamic and kinematic interactions in quiescent fluids. When flow is imposed into the channel, the buoyancy effect is however significantly suppressed. Additionally, the drift velocity perpendicular to the buoyancy vector as a result of chirality-induced transverse swimming decreases with buoyancy force. However, this transverse drift capability is recovered after excluding the intrinsic swimming motility in a quiescent medium. Failing to escape from the trapping as a result of buoyant force allows for a facile separation of bacteria along the vertical direction. The findings also offer a controllable way to redisperse and homogenize the bacteria distribution close to walls by imposing a weak shear flow.

Weak reproductive isolation and extensive gene flow between Mimulus glaucescens and M. guttatus in northern California.

Barriers to reproduction are often how progress in speciation is measured. Nonetheless, an unresolved question concerns the extent to which reproductive barriers diminish gene flow between incipient species. The Sierra Nevada foothill endemic Mimulus glaucescens and the widespread M. guttatus are considered distinct species based on striking differences in vegetative morphology, but barriers to reproduction have not been previously identified, nor has gene flow between species been characterized. Here, we examined 15 potential reproductive barriers within a Northern California area of broad sympatry. Most barriers, with the exception of ecogeographic isolation, were weak or absent, and total isolation for each species was incomplete. Population genomic analyses of range-wide and broadly sympatric accessions revealed extensive gene flow between these taxa, particularly in sympatry. Despite widespread introgression, Mimulus glaucescens, emerged as monophyletic and largely comprised a single ancestry that was found at intermediate frequency within M. guttatus. This result, along with observed ecological and phenotypic differentiation, suggests that natural selection may contribute to the maintenance of distinct phenotypic forms in the earliest stages of speciation. Integrating estimates of barrier strength with direct estimates of gene flow can strengthen a more nuanced interpretation of the process of speciation in natural communities.

Occurrence and risk assessment of total mercury, methylmercury and other selected trace metals in the surface sediments of the Cochin Estuary, Southwest Coast of India

This study assesses the ecological risk and impact of anthropogenic activities in the Cochin estuary – a Ramsar site – by trace metal indices in surface sediment collected from thirteen sampling stations in three seasons. The trace metals analyzed are THg, MeHg, Pb, Cu, Cd, Zn, Ni, Co, Mn, Cr, Fe, and Al in the surface sediments and their spatio-temporal variation is recorded. Pollution indices (i.e., Enrichment factor, Index of geoaccumulation, sediment quality guidelines, pollution load index, and potential ecological risk index) were applied to ascertain the sediment quality. The distribution pattern of Cr, Zn, and Cd revealed higher concentrations in the northern arm of the estuary and near the industrial regions indicating non-geogenic inputs. The concentration of THg and MeHg exhibited spatial and temporal variations and were higher than the background values. The results showed that higher levels of trace metals were found in the northern part of the Cochin Estuary, which could be attributed to the weak flow and significant input of industrial effluents.

Smoke dispersion test and emergency control plan of fire in mine roadway during downward ventilation

To explore the wind flow turbulence and smoke flow diffusion law during the mine downward ventilation fire, two similar experimental platforms of a inclined single pipe test device and a loop system multiple pipe test device were built. The change data of the air flow in the pipeline during the fire period under different air volumes were measured. The evolution process of downward ventilation fire in the whole roadway network domain in Dayan Mine was simulated, and the emergency plan was put forward. The results show that in the experiment, the combustion intensity of the fire source is positively correlated with the ventilation power, and the fire wind pressure increases with the increase of the inclination angle of the pipeline. The throttling effect of the fire area and the combustion of the fire source together make the air volume in the pipeline change rapidly. The critical wind speed that makes the downward ventilation flow fire wind pressure equal to the fan power is 1.8 m s−1. The stronger the fan capacity, the stronger the ability of the main air path to overcome the resistance of the fire zone and maintain the original state. In the simulation, the most dangerous place when the downward ventilation fire smoke is reversed is the area (weak flow area) in the mine tunnel network where the ventilation power is weaker than the fire wind power. This study can provide a theoretical basis for the formulation of emergency plans for mine fire accidents.

Modulation of daily PM2.5 concentrations over China in winter by large-scale circulation and climate change

Abstract. We use the United Kingdom Earth System Model, UKESM1, to investigate the influence of the winter large-scale circulation on daily concentrations of PM2.5 (particulate matter with an aerodynamic diameter of 2.5 µm or less) and their sensitivity to emissions over major populated regions of China over the period 1999–2019. We focus on the Yangtze River delta (YRD), where weak flow of cold, dry air from the north and weak inflow of maritime air are particularly conducive to air pollution. These provide favourable conditions for the accumulation of local pollution but limit the transport of air pollutants into the region from the north. Based on the dominant large-scale circulation, we construct a new index using the north–south pressure gradient and apply it to characterise PM2.5 concentrations over the region. We show that this index can effectively distinguish different levels of pollution over YRD and explain changes in PM2.5 sensitivity to emissions from local and surrounding regions. We then project future changes in PM2.5 concentrations using this index and find an increase in PM2.5 concentrations over the region due to climate change that is likely to partially offset the effect of emission control measures in the near-term future. To benefit from future emission reductions, more stringent emission controls are required to offset the effects of climate change.

Influences of Urbanization on an Afternoon Heavy Rainfall Event over the Yangtze River Delta Region

Abstract An afternoon heavy rainfall event occurred over coastal Nantong, an area of 70–100 km downstream from the Shanghai–Suzhou–Wuxi–Changzhou city belt over the Yangtze River Delta, under the influences of weak southwesterly monsoonal flows and lake/sea breezes on 26 July 2018. An observational analysis shows the emergence of pronounced urban heat island (UHI) effects along the city belt during the late morning hours. A series of nested-grid cloud-permitting model simulations with the finest grid spacing of 1 km are performed to examine the impacts of urbanization on convection initiation (CI) and the subsequent heavy rainfall event. Results reveal the generation of lake breezes and warm anomalies in the planetary boundary layer along the city belt and low-level convergence, thereby inducing upward motion for CI. The southwesterly flows of the monsoonal warm–moist air, enhanced by the UHI effects along the city belt, allow the development of convective cells along the city belt, some of which merge with convective clusters during their downstream propagation, and the ultimate generation of several distinct heavy rainfall centers by local convective clusters over coastal Nantong where atmospheric columns are more moist and potentially unstable under the influences of sea breezes. Sensitivity simulations show small contribution of Nantong’s UHI effects to the heavy rainfall event. The above findings help elucidate how the UHI effects could assist the CI in a weak-gradient environment, and explain why urbanization can contribute to increased downwind mean and extreme precipitation under the influences of favorable regional forcing conditions. Significance Statement The urban heat island (UHI) effects tend to produce more rainfall on its downwind side than that on the other sides, but alone could hardly account for the generation of heavy rainfall. This study examines the influences of the UHI effects associated with a city belt over the Yangtze River Delta on generating an afternoon heavy rainfall event over coastal Nantong that is 70–100 km downwind from the city belt. Results show (i) the downwind advection of the UHI effects; (ii) the initiation of convective storms along the city belt, and their subsequent downstream propagation, leading to the generation of heavy rainfall over Nantong; and (iii) an important role of sea breezes in generating the heavy rainfall event.

Characteristics of a Seasonal Front in the Southern Bay of Bengal: Dynamics, Mixing, and Water Mass Transport

Abstract The formation of a sharp oceanic front located south-southeast of Sri Lanka during the southwest monsoon is examined through in situ and remote observations and high-resolution model output. Remote sensing and model output reveal that the front extends approximately 200 km eastward from the southeast coast of Sri Lanka toward the southern Bay of Bengal (BoB). This annually occurring front is associated with the boundary between the southwest monsoon current with high-salinity water to the south, and a weak flow field comprised of relatively fresh BoB water to the north. The front contains a line of high chlorophyll extending from the coastal upwelling zone, often for several hundred kilometers. Elevated turbulent diffusivities ∼10−2 m2 s−1 along with large diapycnal fluxes of heat and salt were found within the front. The formation of the front and vertical transports are linked to local wind stress curl. Large vertical velocities (∼50 m day−1) indicate the importance of ageostrophic, submesoscale processes. To examine these processes, the Ertel potential vorticity (PV) was computed using the observations and numerical model output. The model output shows a ribbon of negative PV along the front between the coastal upwelling zone and two eddies (Sri Lanka Dome and an anticyclonic eddy) typically found in the southern BoB. PV estimates support the view that the flow is susceptible to submesoscale instabilities, which in turn generate high vertical velocities within the front. Frontal upwelling and heightened mixing show that the seasonal front is regionally important to linking the fresh surface water of the BoB with the Arabian Sea. Significance Statement Within the ocean, motions span extraordinarily wide ranges of sizes and time scales. In this study we focus on a narrow, intensified feature called a front. This front occurs in the southern Bay of Bengal during the summer monsoon and forms a boundary between fresher water to the north and saltier water to the south. Features such as this are difficult to study, however, by combining observations made from ships and satellites with output from numerical models of the ocean, we are able to better understand the front. This is important because fronts like the one studied here play a role in determining the pathways of heat within the ocean, which, in turn, may feedback into the atmosphere and weather patterns.

Numerical Study of Compressible and Weak Compressible Flows in Channel Based on Artificial Compressibility Method and Fully Artificial Compressibility Method

In this article, a numerical study of compressible and weak compressible Newtonian flows is achieved for a time marching, Galerkin algorithm. A comparison between two numerical techniques for such flows, namely the artificial compressibility method (AC–method) and the fully artificial compressibility method (FAC–method) is performed. In the first artificial compressibility parameter ( is added to the continuity equation, while this parameter is added to both continuity and momentum equations in the second technique. This strategy is implemented to treat the governing equations of Newtonian flow in cylindrical coordinates (axisymmetric). Particularly, this study concerns with the effect of the artificial compressibility parameters on the convergence level of solutions components. To confirm the analysis of these approaches, Poiseuille flow along a circular channel under an isothermal state is used as a simple test problem. The results show that when the AC-method is used there is a significant reduction in the level of time convergence of pressure and axial velocity compared to that with FAC-method. Here, for compressible flow the Tail model of state is employed to relate the pressure to density. In this context, the effect of Tail parameters and Reynolds number on the time convergence of solution components is also investigated in the present study. The results indicate a significant reduction in the time-stepping convergence as increasing in the {B,m}-value. In contrast, more difficulties are faced in the convergence when the level of the Reynolds number is increasing.

Effectively reutilizing waste clay brick to prepare a novel green foam concrete base on a new two-step paste substitution method

Waste clay brick is the most common demolition waste in China. Such numerous bricks are dumped in landfills, which cause great pressure to environment. Existing research reported that clay brick could partially replace aggregate or cement to prepare ordinary concrete, but only in a small amount, because of the weak flow spread, high water absorption, and low compressive strength of the mixtures. This work proposed an effective reutilizing technology of this waste to make high-strength foamed concrete (FC), in which discarded clay brick was rolled into clay brick powder (CBP) and then went through an innovative two-stage gelatinization replacement process. Totally 39 groups of 117 specimens were employed to investigate the influence of CBP dosage and water/cement (W/C) ratio on flow spread, water absorption, compressive behavior, and pore structure. Results show that the CBP dosage could rise to 12% without do harm to workability while the compressive strength of FC increased to 3.21 MPa (grew by 286% in maximum), the pore size distribution was measured as 89.57% in 0.50 to 1 mm range, and the porosity raised about 52.46%. Finally, the technologies of scanning electron microscope (SEM) and X-ray diffractometer (XRD) were used to analyze the microstructure and composition of specimen, confirming that the hydrates in CBP and FC blends primarily consisted of Ca(OH)2 and calcium silicate hydrate (C-S-H) gel. Pozzolanic reaction products formed in mixtures, including hydrates of calcium silicates (CSH), aluminates (CAH) and aluminosilicates (CASH), resulting in consumption of Ca(OH)2, which could make the microstructure denser and obtain stronger compressive strength growth at 28-day. This research can provide guidance and theoretical support for high utilization of waste clay brick to prepare FC green construction materials.