Specific Flow Patterns Research Articles

Drug targeting investigation in the critical region of the arterial bypass graft

Abstract Magnetic targeting is a non-invasive strategy to improve treatment efficacy for graft intimal hyperplasia (the leading cause of the arterial bypass graft failure). The present study aims are to investigate the possibility of MPs retention in the bypass graft anastomosis region where IH are developed after surgical intervention and quantify the particles accumulation function of the position of the external magnetic field. In this study iron (Fe) particles with 10 μm in size were used to model the magnetic carrier mixed in the glycerol-water solutions. The 10 μm diameter iron particle was used only to model the magnetic carrier in experimental investigation (not intended for clinical use), to demonstrate the feasibility of the particle targeting. Magnetic fields are generated by NdFeB external magnet. Positioning permanent magnet near to the diseased area resulted in a deviation of the injected ferromagnetic particles within the blood flux and their capture onto the wall of the bypass graft test section. To increase the accumulation of the particles in the targeted region, it is critical to understand the effect of the flow structure on particle deposition, namely interaction between the instabilities formed in the primary vortex of the anastomosis region. The results presented in this paper, put in evidence the blood constituents migrations to the artery wall for the specific flow pattern (through used iron particles), and demonstrate the feasibility of the magnetic drug targeting as a potential alternative method for effective treatment of the bypass graft intimal hyperplasia.

A new hypothesis on the role of vessel topology in cerebral aneurysm initiation

Aneurysm pathogenesis is thought to be strongly linked with hemodynamical effects. According to our current knowledge, the formation process is initiated by locally disturbed flow conditions. The aim of the current work is to provide a numerical investigation on the role of the flow field at the stage of the initiation, before the aneurysm formation. Digitally reconstructed pre-aneurysmal geometries are used to examine correlations of the flow patterns to the location and direction of the aneurysms formed later. We argue that a very specific rotational flow pattern is present in all the investigated cases marking the location of the later aneurysm and that these flow patterns provide the mechanical load on the wall that can lead to a destructive remodelling in the vessel wall. Furthermore, these patterns induce elevated vessel surface related variables (e.g. wall shear stress (WSS), wall shear stress gradient (WSSG) and oscillatory shear index (OSI)), in agreement with the previous findings. We emphasise that the analysis of the flow patterns provides a deeper insight and a more robust numerical methodology compared to the sole examination of the aforementioned surface quantities.

Experimental and numerical study on the flow behavior in a jet-driven swirling flow

ABSTRACTIn order to understand the asphalt separation processes in a new technique of solvent deasphalting, the hydrodynamics of the jet-driven swirling flow within a spray granulation tower (SGT) was studied by using experimental and numerical methods. Mean velocity components were measured by use of the Phase Doppler Particle Anemometer (PDPA). Simulation with Reynolds Stress Model (RSM) was carried out to understand the flow information. Two different zones in the jet-driven swirling flow were observed in both experiment and simulation. A combined effect of jet, jet entrainment and jet interactions leads to complex flow behavior in the upper part. A double swirling flow was identified on the basis of the tangential and the axial velocity distribution in the lower part. The specific flow pattern was identified based on the experimental and computational flow field. An empirical formula was proposed to predict the percentage of the SGT occupied by the jet and the swirl zone.

Flow hydrodynamics of immiscible liquids with low viscosity ratio in a rectangular microchannel with T-junction

We present an experimental study of the liquid-liquid system with extremely low viscosity ratio (10−3) in a T-shaped microchannel with 120 × 120 μm inlets and a 240 × 120 μm outlet channel. Six different flow patterns have been observed: plug, droplet, slug, throat-annular and parallel flow. A specific plug flow pattern was found where micron-sized droplets or even a jet breaks off from the rear meniscus of a plug. In addition to typical Taylor-shaped plugs the dumbbell-like plugs were observed. Flow visualization data were summarized in the flow pattern maps. Plug length and velocity were measured based on flow visualization results. It was found that the plug velocity can be fitted by power function rather than the linear function, which disagrees with experimental data at a low plug velocity. Front and tail plug surface curvature was scaled using dimensionless parameter, the flow rate ratio multiplied by Capillary number based on bulk velocity (Qd/Qc * Cabulk). Instantaneous velocity vector fields inside water plugs were measured by means of PTV technique. Different flow structures were found and discussed. As a result, it is proposed to use the values of Qd/Qc * Cabulk for distinguishing different plug shapes and circulation patterns inside the plugs.

Discrete Element Method Simulation and Experimental Validation of Pattern Development in a Rotating Drum Mixer

AbstractThe handling and processing of powders and granular materials can be crucial for the quality of a final product. Therefore, a detailed description and analysis of granular flow phenomena from first principles is very valuable. In the present study, simulations of granular mixing and segregation of binary‐sized mixtures using a discrete element method were performed for horizontal rotating drum mixers. Numerical results were compared with experimental measurements and significant agreement between both approaches was found. The development of specific flow patterns was observed. The formation of these complex spatiotemporal patterns is influenced by the size of the mixer, the aspect ratio of length to diameter, the rotational speed of the drum, and the initial distribution of the particles.

Borax Crystallization Kinetics in a Pitched‐Blade Turbine/Straight‐Blade Turbine Dual‐Impeller Crystallizer

AbstractThe influence of hydrodynamic conditions on crystallization kinetics and properties of borax crystals obtained in a dual‐impeller batch cooling crystallizer was investigated. The two impellers used, i.e., pitched‐ and straight‐blade turbines, were mounted on the same shaft. Hydrodynamics was analyzed by means of the mixing time values and specific fluid flow patterns generated. Results indicate that wider metastable zones were generally observed at impeller positions characterized by longer mixing times. In those cases, the growth rate constants were lower, resulting in a formation of smaller but more regularly shaped crystals. These findings imply that the dual‐impeller position should be taken into account in order to produce crystals of desired characteristics.

Precipitation regimes over central Greenland inferred from 5 years of ICECAPS observations

Abstract. A novel method for classifying Arctic precipitation using ground based remote sensors is presented. Using differences in the spectral variation of microwave absorption and scattering properties of cloud liquid water and ice, this method can distinguish between different types of snowfall events depending on the presence or absence of condensed liquid water in the clouds that generate the precipitation. The classification reveals two distinct, primary regimes of precipitation over the Greenland Ice Sheet (GIS): one originating from fully glaciated ice clouds and the other from mixed-phase clouds. Five years of co-located, multi-instrument data from the Integrated Characterization of Energy, Clouds, Atmospheric state, and Precipitation at Summit (ICECAPS) are used to examine cloud and meteorological properties and patterns associated with each precipitation regime. The occurrence and accumulation of the precipitation regimes are identified and quantified. Cloud and precipitation observations from additional ICECAPS instruments illustrate distinct characteristics for each regime. Additionally, reanalysis products and back-trajectory analysis show different synoptic-scale forcings associated with each regime. Precipitation over the central GIS exhibits unique microphysical characteristics due to the high surface elevations as well as connections to specific large-scale flow patterns. Snowfall originating from the ice clouds is coupled to deep, frontal cloud systems advecting up and over the southeast Greenland coast to the central GIS. These events appear to be associated with individual storm systems generated by low pressure over Baffin Bay and Greenland lee cyclogenesis. Snowfall originating from mixed-phase clouds is shallower and has characteristics typical of supercooled cloud liquid water layers, and slowly propagates from the south and southwest of Greenland along a quiescent flow above the GIS.

Gas-liquid two-phase flow measurements by the electromagnetic flowmeter combined with a phase-isolation method

The electromagnetic flowmeter has presented excellent performance in single-phase flow. However, there are many fundamental difficulties when it is applied in two-phase flow. The presence of the insulating phase at various positions in two-phase flow strongly influences the distribution of the weight function, consequently resulting in the uncertainty and instability of the electromagnetic flowmeter's output. When the insulating phase contact with the electrode, it even leads to wrong alarm. In this paper, at the upstream of the electromagnetic flowmeter a phase-isolation method was used to change the inlet flow pattern into a uniform and symmetrical swirling core-annular flow, in which gas-liquid mixture was isolated to gas core and liquid annular flows flowing concurrently in the transmission pipe with a clear smooth interface between them. Then we analysed the behavior of the electromagnetic flowmeter performed in this specific flow pattern, and built the liquid flow rate measurement model. Besides, the void fraction was measured by image processing technique. Owing to the clear smooth interface, the difficulty of image processing and the measurement error of the void fraction can be reduced. The experimental results showed that, the combination of the phase-isolation method could improve the measurement accuracy and successfully make the electromagnetic flowmeter available for the gas-liquid two-phase flow where the original phase distribution is not uniform.

Cerebrospinal and interstitial fluid transport via the glymphatic pathway modeled by optimal mass transport

The glymphatic pathway is a system which facilitates continuous cerebrospinal fluid (CSF) and interstitial fluid (ISF) exchange and plays a key role in removing waste products from the rodent brain. Dysfunction of the glymphatic pathway may be implicated in the pathophysiology of Alzheimer's disease. Intriguingly, the glymphatic system is most active during deep wave sleep general anesthesia. By using paramagnetic tracers administered into CSF of rodents, we previously showed the utility of MRI in characterizing a macroscopic whole brain view of glymphatic transport but we have yet to define and visualize the specific flow patterns. Here we have applied an alternative mathematical analysis approach to a dynamic time series of MRI images acquired every 4min over ∼3h in anesthetized rats, following administration of a small molecular weight paramagnetic tracer into the CSF reservoir of the cisterna magna. We use Optimal Mass Transport (OMT) to model the glymphatic flow vector field, and then analyze the flow to find the network of CSF-ISF flow channels. We use 3D visualization computational tools to visualize the OMT defined network of CSF-ISF flow channels in relation to anatomical and vascular key landmarks from the live rodent brain. The resulting OMT model of the glymphatic transport network agrees largely with the current understanding of the glymphatic transport patterns defined by dynamic contrast-enhanced MRI revealing key CSF transport pathways along the ventral surface of the brain with a trajectory towards the pineal gland, cerebellum, hypothalamus and olfactory bulb. In addition, the OMT analysis also revealed some interesting previously unnoticed behaviors regarding CSF transport involving parenchymal streamlines moving from ventral reservoirs towards the surface of the brain, olfactory bulb and large central veins.

An improved criterion to select dominant modes from dynamic mode decomposition

Dynamic mode decomposition (DMD) has been extensively utilized to analyze the coherent structures in many complex flows. Although specific flow patterns with dominant frequency and growth rate can be captured, extracting dominant DMD modes for flow reconstruction and dynamic modeling still needs a priori knowledge on flow physics, especially for some transient states of unstable flows. In this paper, a criterion to select dominant modes from DMD technique is developed. The unsteady flow can be described by the superposition of each normalized DMD mode multiplied by its time coefficient. The dominance of each DMD mode can be ordered by time integration of its time coefficient. Compared with standard DMD approach, which decides the dominance of DMD modes from the order of amplitude or mode norm, this criterion considers the evolution of each mode within the whole sampling space, and ranks them according to their contribution to all samples. The proposed mode selection strategy is evaluated by test cases including both equilibrium and transient states of a cylinder at Reynolds number of 60 and a transient state of a NACA0012 airfoil buffeting in transonic flow. Results indicate that using this criterion, dominant DMD modes can be identified and flow dynamics in unstable or transient systems can be reconstructed accurately with fewer modes. Besides, this approach has better convergence against mode number and lower sensitivity to the initial condition than standard DMD method.

DroidNative: Automating and optimizing detection of Android native code malware variants

According to the Symantec and F-Secure threat reports, mobile malware development in 2013 and 2014 has continued to focus almost exclusively (~99%) on the Android platform. Malware writers are applying stealthy mutations (obfuscations) to create malware variants, thwarting detection by signature-based detectors. In addition, the plethora of more sophisticated detectors making use of static analysis techniques to detect such variants operate only at the bytecode level, meaning that malware embedded in native code goes undetected. A recent study shows that 86% of the most popular Android applications contain native code, making native code malware a plausible threat vector. This paper proposes DroidNative, an Android malware detector that uses specific control flow patterns to reduce the effect of obfuscations and provides automation. As far as we know, DroidNative is the first system that builds cross-platform (x86 and ARM) semantic-based signatures at the Android native code level, allowing the system to detect malware embedded in either bytecode or native code. When tested with a dataset of 5490 samples, DroidNative achieves a detection rate (DR) of 93.57% and a false positive rate of 2.7%. When tested with traditional malware variants, it achieves a DR of 99.48%, compared to the DRs of academic and commercial tools that range from 8.33% to 93.22%.

Two-phase flow patterns in adiabatic and diabatic corrugated plate gaps

Correlations for two-phase heat transfer and pressure drop can be improved considerably, when they are adapted to specific flow patterns. As plate heat exchangers find increasing application as evaporators and condensers, there is a need for flow pattern maps for corrugated plate gaps. This contribution presents experimental results on flow pattern investigations for such a plate heat exchanger background, using an adiabatic visualisation setup as well as a diabatic setup.Three characteristic flow patterns were observed in the considered range of two-phase flow: bubbly flow, film flow and slug flow. The occurrence of these flow patterns is a function of mass flux, void fraction, fluid properties and plate geometry. Two different plate geometries having a corrugation angle of 27° and 63°, respectively and two different fluids (water/air and R365mfc liquid/vapor) have been analysed. A flow pattern map using the momentum flux is presented.

Derivation of flow related risk indices for stenosed left anterior descending coronary arteries with the use of computer simulations

The geometry of the coronary vessel network is believed to play a decisive role in the initiation, progression and outcome of coronary artery disease (CAD) and the occurrence of acute coronary syndromes (ACS). It also determines the flow field in the coronary artery which can be linked to CAD evolution.In this work geometric 3D models of left anterior descending (LAD) coronary arteries associated with either myocardial infarction (MI) or stable (STA) CAD were constructed. Transient numerical simulations of the flow for each model showed that specific flow patterns develop in different extent in the different groups examined. Recirculation zones, present distal the stenosis in all models, had larger extent and duration in MI cases. For mild stenosis (up to 50%) areas with low time averaged wall shear stress TAWSS (<0.15Pa) as well as areas with high TAWSS (>3Pa) appeared only in MI models; in moderate and severe stenosis (>50%) these areas were present in all models but were significantly larger for MI than STA models. These differentiations were expressed via numerical indices based on TAWSS, oscillating shear index (OSI) and relative residence time (RRT). Additionally we introduced the coagulation activation index (CAI), based on the threshold behaviour of coagulation initiation, which exceeded the suggested threshold only for MI models with intermediate stenosis (up to 50%). These results show that numerical simulations of flow can produce arithmetic indices linked with the risk of CAD complications.

Flow Stability Model of Centrifugal Compressors Based on Eigenvalue Approach

A stall inception model of centrifugal compressors is developed on the basis of the global stability analysis in the present paper. This model takes specific flow patterns and impeller geometry into account, which can be used to analyze the effect of blade design parameters on the stall limit of centrifugal compressors. In particular, the body force model and the solution of the stability eigenvalue equation are two important problems to be addressed in this frame. The spectral method and singular value decomposition are used to discrete stability equations to obtain the eigenvalues. By applying conservation laws, a perturbation-response form of the body force, specifically for centrifugal compressor, is also established to simulate blade behavior. Two different forms (the meridional model and the normal expansion model) are derived to make a comparison of grid independence and computation time. The capacity of these models is assessed against the experimental data of a NASA low-speed centrifugal compressor rotor. The results show that these models could be used to predict stall onset with acceptable accuracy and low computational cost.

Chaotic micromixer utilizing electro-osmosis and induced charge electro-osmosis in eccentric annulus

Efficient mixing is of significant importance in numerous chemical and biomedical applications but difficult to realize rapidly in microgeometries due to the lack of turbulence. We propose to enhance mixing by introducing Lagrangian chaos through electro-osmosis (EO) or induced charge electro-osmosis (ICEO) in an eccentric annulus. The analysis reveals that the created Lagrangian chaos can achieve a homogeneous mixing much more rapidly than either the pure EO or the pure ICEO. Our systematic investigations on the key parameters, ranging from the eccentricity, the alternating time period, the number of flow patterns in one time period, to the specific flow patterns utilized for the Lagrangian chaos creation, present that the Lagrangian chaos is considerably robust. The system can obtain a good mixing effect with wide ranges of eccentricity, alternating time period, and specific flow patterns utilized for the Lagrangian chaos creation as long as the number of flow patterns in one time period is two. As the electric field increases, the time consumption for homogenous mixing is reduced more remarkably for the Lagrangian chaos of the ICEO than that of the EO.

Microconnectomics of the pretectum and ventral thalamus in the chicken (Gallus gallus).

The avian pretectal and ventrothalamic nuclei, encompassing the griseum tectale (GT), n. lentiformis mesencephali (LM), and n. geniculatus lateralis pars ventralis (GLv), are prominent retinorecipient structures related to optic flow operations and visuomotor control. Hence, a close coordination of these neural circuits is to be expected. Yet the connectivity among these nuclei is poorly known. Here, using intracellular labeling and in situ hybridization, we investigated the detailed morphology, connectivity, and neurochemical identity of neurons in these nuclei. Two different cell types exist in the GT: one that generates an axonal projection to the optic tectum (TeO), LM, GLv, and n. intercalatus thalami (ICT), and a second population that only projects to the LM and GLv. In situ hybridization revealed that most neurons in the GT express the vesicular glutamate transporter (VGluT2) mRNA, indicating a glutamatergic identity. In the LM, three morphological cell types were defined, two of which project axons towards dorsal targets. The LM neurons showed strong VGluT2 expression. Finally, the cells located in the GLv project to the TeO, LM, GT, n. principalis precommisuralis (PPC), and ICT. All neurons in the GLv showed strong expression of the vesicular inhibitory amino acid transporter (VIAAT) mRNA, suggesting a GABAergic identity. Our results show that the pretectal and ventrothalamic nuclei are highly interconnected, especially by glutamatergic and GABAergic neurons from the GT and GLv, respectively. This complex morphology and connectivity might be required to organize orienting visuomotor behaviors and coordinate the specific optic flow patterns that they induce. J. Comp. Neurol. 524:2208-2229, 2016. © 2015 Wiley Periodicals, Inc.

Experimental and numerical study on heat transfer in trailing edge cooling passages with dimples/protrusions under the effect of side wall slot ejection

Combined experimental and numerical studies were conducted on the heat transfer and pressure performance in gas turbine trailing edge rectangular and trapezoidal cooling passages with ejection slots. Considering the space restrictions inside narrow cooling channel near trailing edge and pressure drop considerations, dimple and protrusion structures are adopted as heat transfer enhancement devices inside cooling channel. Experimental study is based on transient infrared thermography technique and numerical study is based on RANS method using commercial software CFX. In this study, rectangular channel and trapezoidal channel are both investigated with and without ejection slots. The effects of channel cross-section, roughened structures and slot ejection are considered. From the results, the flow characteristics near roughened structures and ejection slots are obtained. Mechanisms of heat transfer enhancement are explained according to specific flow patterns. Meanwhile, the Nusselt number distributions on channel surface are presented by both methods. The heat transfer enhancement capability of each channel configuration is evaluated and comparisons of infrared results and numerical predictions are made. Finally, the channel overall heat transfer coefficient and friction ratio are evaluated on each configuration. Summarizing the results, it can be estimated that, the cooling performance inside trailing edge internal cooling passages can be elevated by arranging dimples and protrusions, or the combination with other typical devices such as ribs or pin–fins.

Relationship between Oral Flow Patterns, Nasal Obstruction, and Respiratory Events during Sleep.

Sleep breathing patterns are altered by nasal obstruction and respiratory events. This study aimed to describe the relationships between specific sleep oral flow (OF) patterns, nasal airway obstruction, and respiratory events. Nasal flow and OF were measured simultaneously by polysomnography in 85 adults during sleep. OF was measured 2 cm in front of the lips using a pressure sensor. OF could be classified into three patterns: postrespiratory event OF (postevent OF), during-respiratory event OF (during-event OF), and spontaneous arousal-related OF (SpAr-related OF). Postevent OFs begin at the end of airflow reduction, are preceded by respiratory arousal, and are accompanied by postapneic hyperventilation; during-event OFs occur during nasal flow reduction; and SpAr-related OFs to OF begin during stable breathing, and are preceded by spontaneous arousal but are rarely accompanied by apnea/hypopnea. Multivariate regression showed that nasal obstruction was predictive of SpAr-related OF. The relative frequency of SpAr-related OF events was negatively correlated with the apnea-hypopnea index. The fraction of SpAr-related OF duration relative to total OF duration was significantly greater in patients with nasal obstruction than in those without. SpAr-related OF was associated with nasal obstruction, but not respiratory events. This pattern thus functions as a "nasal obstruction bypass", mainly in normal subjects and patients with mild sleep disordered breathing (SDB). By contrast, the other two types were related to respiratory events and were typical patterns seen in patients with moderate and severe SDB.

A novel design method based on flow pattern construction for flow passage with low flow drag and pressure drop

A novel design method for flow passage with low flow drag and pressure drop was developed based on flow pattern construction. The specific flow pattern with minimum viscous dissipation rate represents low pressure drop in the flow passage. Thus, the fluid flow requires to be optimized as a variational problem subject to the minimum viscous dissipation rate principle, which is also considered as flow pattern construction. By using calculus of variations, the governing equations for the construction of the specific flow pattern were derived from the functional extremum problem represented by the Lagrange multiplier equation. After that, a computational fluid dynamics model was set up and applied in the solution procedure of the governing equations to generate the geometry of the flow passages based on the flow pattern construction. As the illustrative examples to validate the proposed design method, the geometries of flow passages were optimized in terms of pressure drop in a wide range of Re numbers.

Two-phase pressure drops and flow pattern observations in 90° bends subject to upward, downward and horizontal arrangements

In this study, single-phase/two-phase frictional characteristics and flow patterns of 90° bends are experimentally investigated. The two bends have inner diameters (D) of 5.5 and 9.5mm with tube curvature ratio (2R/D) of 5.4 and 4.2, respectively. The bends are installed either an upward, horizontal or downward arrangement. For results concerned with single-phase flow, the bend friction factor (fB) is always greater than that of the straight tubes at the same liquid Reynolds number. On the other hand, the fB values for D=9.5mm with smaller curvature ratio are greater than those of D=5.5mm. The resultant two-phase frictional pressure drops of 90° bend are well predicted by the Sánchez Silva et al. [14]’s correlation. For the two-phase frictional pressure gradient, the upward arrangement is greater than that of the horizontal arrangement due to swirled motion and liquid flow reversal. The flow reversals are observed for upward flow arrangement at specific flow pattern and pressure gradient. However, no swirled motion and liquid flow reversal is seen in the downward arrangement. As mass flux and quality increase, the differences of pressure drop among the three arrangements are getting smaller due to the appreciable offset by the rising flow inertia. Meanwhile, the liquid flow reversal is more evidently observed in the large diameter bend. Flow pattern map showing the region of liquid flow reversal is shown on the diagram of the superficial gas velocity (UGS) versus superficial liquid velocity (ULS). The region for liquid flow reversal for D=9.5mm is much greater than that of D=5.5mm. For D=5mm, there is no liquid flow reversal when UGS is above 2m/s. On the other hand, the threshold value is raised to 4m/s for the 9.5mm internal diameter tube.