Obtained Flow Field Research Articles

Craniocerebral Dynamic Response and Cumulative Effect of Damage Under Repetitive Blast.

Soldiers suffer from multiple explosions in complex battlefield environment resulting in aggravated brain injuries. At present, researches mostly focus on the damage to human body caused by single explosion. In the repetitive impact study, small animals are mainly used for related experiments to study brain nerve damage. No in-depth research has been conducted on the dynamic response and damage of human brain under repetitive explosion shock waves. Therefore, this study use the Euler-Lagrange coupling method to construct an explosion shock wave-head fluid-structure coupling model, and numerically simulated the brain dynamic response subjected to single and repetitive blast waves, obtained flow field pressure, skull stress, skull displacement, intracranial pressure to analyze the brain damage. The simulation results of 100g equivalent of TNT exploding at 1m in front of the craniocerebral show that repetitive blast increase skull stress, intracranial pressure, skull displacement, and the damage of brain tissue changes from moderate to severe. Repetitive blasts show a certain cumulative damage effect, the severity of damage caused by double blast is 122.5% of single shock, and the severity of damage caused by triple blast is 105.9% of double blast and 131.5% of single blast. The data above shows that it is necessary to reduce soldiers' exposure from repetitive blast waves.

Recirculating flow-induced anomalous transport in meandering open-channel flows

Channel meanders in rivers induce complex three-dimensional (3D) flow characteristics such as secondary flows and flow recirculation. Helical secondary flows promote transverse dispersion, and flow recirculation zones trap tracers. As a result, these meander-driven flows may cause anomalous transport manifested by unusually elevated levels of tracer concentration at early and late times of breakthrough curves (BTCs). In this study, we perform 3D numerical simulations in meandering channels across a wide range of channel sinuosity to investigate the impact of meander geometry on flow and transport. We solve 3D Reynolds-averaged Navier-Stoke equations blended with a SST k − ω turbulence model to obtain velocity and turbulence fields. We then incorporate the obtained flow fields into a Lagrangian particle tracking model to simulate solute transport. Sinuosity higher than 1.5 leads to the onset of horizontal recirculating flows along the apex outer banks, and these recirculation zones expand as sinuosity increases. The analysis of the transport simulations elucidates that the interplay between the secondary flows and recirculation zones induces anomalous transport. The helical secondary flows bring particles into the recirculation zones by promoting transverse dispersion, and the recirculating flows delay particle transport by the trapping effect. We show that the tail power-law slope and truncated time of BTCs as well as Lagrangian tortuosity distributions change dramatically with the emergence of recirculation zones. These analyses demonstrate that the recirculation zones are acting as the primary driver of anomalous transport. Finally, we successfully predict the observed anomalous transport with a Spatial Markov Model (SMM), which is an upscaled transport model that incorporates Lagrangian velocity distribution and spatial velocity correlation. The successful predictions show that the Lagrangian velocity statistics effectively capture the underlying mechanisms of anomalous transport in meandering open-channel flows.

Hemodynamics Changes in Aortic Flux Due to TEVAR Quantified by 4D-flow-MRI

Introduction: TEVAR (Thoracic endovascular aortic repair) in traumatic aorta injury has shown good long-term results (1). The interaction between endograft and the dynamic anatomy of the thoracic aorta is not well characterized for repetitive physiologic stressors and subsequent issues related to long-term durability. TEVAR could also modify the flow and in the long term increase the risk of cardiovascular diseases (2). The alteration of flow characteristics in the heart and aorta have been related to atherosclerosis, aneurysms, and hypertension (3). The hemodynamic patterns alterations that occur in the aorta after performing TEVAR have not been previously described. The description of these changes could help us understand the pathophysiology of these diseases. The aim of our study was to quantify these changes using 4D-flow-MRI by comparing between healthy volunteer (HV) and TEVAR in trauma patient. Methods: Both individuals underwent non-contrast-enhanced 4D flow-MRI, obtaining flow field and 3D angiography. Geometric and flow parameters were determined at 20 planes positioned from sinotubular junction to proximal DAo. Local vortex characterization was obtained through the computation of in-plane rotational flow (IRF, helical flow) at peak systole and systolic flow reversal ratio (SFRR) (figure 1.A), i.e. the ratio of forward to backward through-plane systolic flow obtained by the time-integral over systolic phases, which is also known as systolic backward flow. Peak-systolic wall shear stress (WSS) was calculated at 64 points equally distributed on the segmented vessel contour. Contour-averaged axial (WSSax) and circumferential WSS (WSScirc) were obtained. Results: The patient with TEVAR presented an abnormal inversion of the direction of the in-plane circulation. Proximal to TEVAR both the patient and the HV presented a clockwise IRF of around 35 cm2/s. However, inside and shortly distally of the TEVAR the patient presented a marked and sustained counterclockwise direction (IRF = -30 cm2/s) while the HV presented clockwise rotation (IRF = 20 cm2/s) (figure 1.B). Similarly, circumferential WSScirc was reversed through the whole length of the TEVAR (figure3). Of note, WSSax was markedly reduced all along the length of the TEVAR (figure 1.C) Conclusion: The presence of TEVAR was associated with abnormal behavior of rotational flow whose eventual consequences are unknown. The reduced friction of the TEVAR inner surface may have repercussion on axial WSS.

Single- and double-helix vortex breakdown as two dominant global modes in turbulent swirling jet flow

In this paper, we study the shape and dynamics of helical coherent structures found in the flow field of an annular swirling jet undergoing vortex breakdown. The flow field is studied by means of time-resolved tomographic particle image velocimetry measurements. The obtained flow fields are analysed using both classic and spectral proper orthogonal decomposition. Despite the simple geometrical set-up of the annular jet, the flow field is very complex. Two distinct large-scale helical flow structures are identified: a single and a double helix, both co-rotating with the swirl direction, and it is revealed that these structures are not higher harmonics of each other. The structures have a relatively low energy content which makes it hard to separate them from other dynamics of the flow field, notably turbulent motions. Because of this, classic proper orthogonal decomposition fails to identify both structures properly. Spectral proper orthogonal decomposition, on the other hand, allows them to be identified accurately when the filter size is set at around eight times the precession period. The precession frequencies of the single and double helices correspond to Strouhal numbers of 0.273 and , respectively. A global stability analysis of the mean flow field shows that these structures correspond to two separate global modes. The precessing frequencies obtained by the stability analysis and the related spatial structures match very well with the experimental observations. The current work extends our knowledge on turbulent vortex breakdown and on mean field global stability theory in general. It leads to the following conclusions. Firstly, single- and double-helix vortex breakdown are both manifestations of global modes. Previous studies have shown that both and modes can coexist in swirling jets. However, the mode has been identified as a second harmonic of the first mode, while this study identifies both as two independent global modes. Secondly, this work shows that the simultaneous occurrence of multiple helical global modes is possible within a turbulent flow and their shapes and frequencies are very well predicted by mean field stability analysis. The latter finding is of general interest as it applies to a wide class of fluid problems dominated by multiple oscillatory structures.

Numerical investigation on the hydrodynamic characteristics of a marine propeller operating in oblique inflow

The hydrodynamic characteristics of a marine propeller operating in oblique inflow are investigated by using CFD method. Two propellers with different geometries are selected as the study subjects. RANS simulation is carried out for the propellers working at a wide range of advance coefficients and incidence angles. The effects of axial inflow and lateral inflow are demonstrated with the hydrodynamic force on the propeller under different working conditions. Based on the obtained flow field details, the hydrodynamic mechanism of propeller operating in oblique inflow is analyzed further. The trailing vortex wake of propeller is highly affected by the lateral inflow, resulting in the deflected development path and the circumferentially non-uniform structure, as well as the enhanced axial velocity in slipstream. Different flow patterns are observed on the propeller blade with the variation of circumferential position. Combined with the computed hydrodynamic forces and pressure distribution on propeller, the mechanism resulting in the increase of propulsive loads and the generation of propeller side force is explored. Finally, a systematic analysis is carried out for the propulsive loads and propeller side force as a function of axial and lateral advance coefficients. The major terms that play a dominant role in the modeling of propulsive loads and propeller side force are determined through the sensitivity analysis. This study provides a deeper insight into the hydrodynamic characteristics of propeller operating in oblique inflow, which is useful to the investigation of propeller performance during ship maneuvers.

Comparison of flow field and combustion in single and double side ported rotary engine

Intake and exhaust ports have great importance on performance of the rotary engines, since flow structure of the combustion chamber is depended on position and geometry of these ports. Similar to reciprocating engines that have different in-flow patterns according to valve characteristics of the engine, the flow patterns inside the combustion chamber change according to port position, quantity and channel geometry of rotary engines. In this study, air flow inside a double-side-ported rotary engine including 4 inlet and 2 exhaust ports with ports was numerically investigated by using computational fluid dynamic techniques. Numerical flow field results were compared with experimental data presented in the literature. Change of volumetric efficiency according to engine speed and flow field data were obtained for different port combinations. The results reveal that swirl and tumble motions are together formed in one side-ported engine simulations. When double-sided-ports are used, tumble motion is prevented by opposing air flow. Results show that double side intake port configuration has highest volumetric efficiency up to 8000 rpm. Single side intake port configuration has high volumetric efficiency up to 3000 rpm and it deteriorates rapidly after 3000 rpm because of high flow frictional losses. For all configurations, it is observed that rotating flows are prevailed by rotor motion at end of compression period and almost similar flow patterns are formed when rotor reaches at top dead center. After obtaining flow field results, combustion of single and double port intake configurations were compared with each other.

Modal analysis of an aerostatic spindle system for ultra-precision machine tools at different spin speeds

The dynamic properties of aerostatic spindle systems vary with the spindle speed and have a significant impact on the processing quality of ultra-precision machine tools. In this article, using the ICEM CFD, the structured grid model of a large-span scale gas film is built under the condition in which the ratio of the spindle gas film length to the gas film thickness is 13,100. Integral calculation model of spindle and thrust is established and CEL expressions are compiled based on dynamic meshing technique to acquire trajectory of aerostatic spindle system. The degree of freedom method is used to obtain flow field of spindle system. Considering the spindle system as an elastomer, the influence of rotational speed on natural frequencies is studied under the flow field boundary. The results indicate that the former four-order natural frequencies of the aerostatic spindle system will clearly increase as the rotational speed increases. The increase in the fifth- to seventh-order natural frequencies is small, and the eighth-order natural frequency is almost invariable. The flow field has little influence on the mode shapes of the aerostatic spindle system. The former four-order natural frequencies of spindle system decrease considering rotation effects. Rotational speed and rotation effects mainly impact the tilting motion natural frequencies of spindle and thrust.

Influence of Loads on Bearing Capacity of Liquid Hydrostatic Bearings

The numerical simulation of liquid hydrostatic bearing by Ansys cfx is carried out and compared with the theoretical formula, the results of the obtained flow field are in agreement with the actual. At the same time, it reveals the effect of load variation on the dynamic characteristics of hydrostatic bearing system under fluctuating load. The result shows: Under the fluctuating load, film thickness, the carrying capacity of different degrees of change. This also provides a basis for the reliability design of hydrostatic support.

ABNORMAL FLOW PATTERN AND GEOMETRY ARE INTERRELATED AND CONTRIBUTE TO PROXIMAL DESCENDING AORTA DILATION IN MARFAN PATIENTS

Objective: Marfan syndrome (MFS) is a hereditary connective tissue disorder caused by mutation in the FBN1 gene. Diseases of the ascending aorta (AAo), like dilation or type A dissection, are very prevalent. However, after improvements in the surgical AAo management, diseases of the descending aorta (DAo) emerged as a clinical issue. Recent qualitative studies in MFS have revealed the existence of abnormal vortex in the proximal DAo which were related to local dilation. However, any study has investigated the origin of these vortices. The aim of the present investigation was to investigate the relationship between aortic geometry and abnormal flow characteristics in the thoracic aorta of MFSDesign and method: Fifty-tree confirmed MFS patients without congenital heart diseases or aortic valve disease were prospectively included from our Aortic unit. Also, 40 age-matched healthy volunteers (HV) were recruited. All participants underwent non-contrast-enhanced 4D flow-MRI, obtaining flow field and angiography. Geometric parameters (diameter, ellipticity and curvature) and rotational flow characteristics (in-plane rotational flow IRF, systolic flow reversal ratio SFRR) were evaluated (see figure 1) at 20 planes through the thoracic aorta. Results: Aortic diameters were significantly-larger in MFS in the proximal AAo (p < 0.001) and in the proximal DAo (p = 0.028) compared to HV, while no differences were found in the remaining region. Ellipticity was increased and peak of aortic curvature was larger and more distal in MFS compared to controls (figure 2) Rotational flow (IRF, related to helicity) was reduced in MFS patients in the majority of the thoracic aorta, while SFRR (backward systolic flow) was increased in the proximal AAo and DAo. Bivariate correlation showed inverse relation between arch ellipticity (R = −0.34, p = 0.016) as well as proximal DAo peak curvature (R = −0.35, p = 0.015) and arch IRF. Maximum proximal DAo diameter was negatively correlated with local IRF (R = −0.3, p = 0.038) and positively correlated with local SFRR (R = 0.605, p < 0.001). Conclusions: Abnormal aortic ellipticity and curvature were evident in MFS patients and related to a reduction of flow helicity and increase of vorticity in the DAo. Longitudinal studies are needed to investigate eventual prognostic value of aortic geometry and flow in MFS patients.

Prograde, retrograde, and oscillatory modes in rotating Rayleigh–Bénard convection

Rotating Rayleigh–Bénard convection is typified by a variety of regimes with very distinct flow morphologies that originate from several instability mechanisms. Here we present results from direct numerical simulations of three representative set-ups: first, a fluid with Prandtl number $Pr=6.4$, corresponding to water, in a cylinder with a diameter-to-height aspect ratio of $\unicode[STIX]{x1D6E4}=2$; second, a fluid with $Pr=0.8$, corresponding to $\text{SF}_{6}$ or air, confined in a slender cylinder with $\unicode[STIX]{x1D6E4}=0.5$; and third, the main focus of this paper, a fluid with $Pr=0.025$, corresponding to a liquid metal, in a cylinder with $\unicode[STIX]{x1D6E4}=1.87$. The obtained flow fields are analysed using the sparsity-promoting variant of the dynamic mode decomposition (DMD). By means of this technique, we extract the coherent structures that govern the dynamics of the flow, as well as their associated frequencies. In addition, we follow the temporal evolution of single modes and present a criterion to identify their direction of travel, i.e. whether they are precessing prograde or retrograde. We show that for moderate $Pr$ a few dynamic modes suffice to accurately describe the flow. For large aspect ratios, these are wall-localised waves that travel retrograde along the periphery of the cylinder. Their DMD frequencies agree with the predictions of linear stability theory. With increasing Rayleigh number $Ra$, the interior gradually fills with columnar vortices, and eventually a regular pattern of convective Taylor columns prevails. For small aspect ratios and close enough to onset, the dominant flow structures are body modes that can precess either prograde or retrograde. For $Pr=0.8$, DMD additionally unveiled the existence of so far unobserved low-amplitude oscillatory modes. Furthermore, we elucidate the multi-modal character of oscillatory convection in low-$Pr$ fluids. Generally, more dynamic modes must be retained to accurately approximate the flow. Close to onset, the flow is purely oscillatory and the DMD reveals that these high-frequency modes are a superposition of oscillatory columns and cylinder-scale inertial waves. We find that there are coexisting prograde and retrograde modes, as well as quasi-axisymmetric torsional modes. For higher $Ra$, the flow also becomes unstable to wall modes. These low-frequency modes can both coexist with the oscillatory modes, and also couple to them. However, the typical flow feature of rotating convection at moderate $Pr$, the quasi-steady Taylor vortices, is entirely absent in low-$Pr$ flows.

Multi-objective optimization of a Stairmand cyclone separator using response surface methodology and computational fluid dynamics

The performance of a cyclone is generally assessed using the pressure drop and the collection efficiency of the cyclone. In the present paper, a multi-objective optimization of a classic Stairmand cyclone separator is executed using the response surface methodology (RSM), combined with computational fluid dynamics (CFD) techniques for minimizing the pressure drop and maximizing the collection efficiency. Ten cyclone geometrical factors are considered in this work. Three of them are studied using the RSM according to the results of the preceding screening experiments. The second-order response surface models for each response are successfully carried out using the central composite design (CCD) in the RSM. The desirability function approach is used to optimize the geometrical factors of the cyclone. In comparison to the reference model, the optimal cyclone model decreases the pressure drop by 20.70% and the cut-off size by 75.38%. The accuracies of the response surface models are confirmed and the correctness of the optimal cyclone model is also validated using CFD; the results indicate excellent performance and reliability of the response surface model and the RSM optimization result. According to the analyses of the obtained flow fields, there are several reasons why decreases in the cut-off size with a lower pressure drop are found in the optimal model. The primary reasons for improvements are optimized values of relevant geometrical factors, the production of a distinct, undisturbed downward flow, an increase in the tangential velocity at the near wall region, and a decrease in the peak tangential velocity.

A study on burning behavior and convective flows in Methanol pool fires bound by ice

Abstract (ID: 2017-170) An experimental study on methanol pool fires bound by ice was carried to research the burning behavior and flow field (within the liquid-phase) of methanol. The experiments were conducted in two parts: 1- in a cylindrical ice cavity/pan (10.2 cm diameter and 6 cm depth) at three different conditions to analyze burning parameters of methanol, 2- in a square glass tray with outside dimensions of 10 × 10 cm and a depth of 5 cm to obtain flow field of methanol pool with a two-dimensional PIV (Particle Image Velocimetry) system. The results of the experiments of the first part show the cold boundaries of the ice cavity/pan act as a heat sink causing considerable heat losses. Thus, burning rates and burning efficiencies are found to be lower with cold boundaries. However, the burning rate values in ice cavity are found to be the highest because of the melting of the ice and expansion of the cavity. The analysis of the results obtained by the PIV system showed the velocity magnitudes and flow patterns in the liquid-phase of icy methanol fire significantly change over the course of burning. In the instants after ignition a horizontal flow induced by Marangoni near the surface was observed. Later on, mixing of melt-water with methanol and sinking of this mixture caused a cycle in the tray that resulted in a vortex appearing in the middle of the pool. Magnitudes of velocity were also observed to increase after ignition. The increase in the velocity magnitudes is expected to significantly impact the melting and size of the lateral cavity.

年間シミュレーションによる結露予測及び結露抑制策の有効性の検討

In recent years, the adoptions of an earth-to-air heat exchanger (EAHE) system to many buildings have been increasing. This system is classified into two types of tube system and underground air tunnel system. There is a problem that an underground air tunnel which is the object of this study is difficult to establish the method of performance prediction since it has a complicated structure. Moreover, this system has an anxiety of air pollution derived from occurrence of dew condensation and continuation of high-humidity environment in a system at operational phases. The occurrences of dew condensation have been predicted by the three-dimensional CFD analysis in several studies. However, these studies are limited to steady state calculation or representative points. The verification of countermeasures of dew condensation has not been carried out by long period and detailed predictions. Originally, EAHE systems should be designed after the identification of the high probability parts of occurrence of dew condensation and the estimation of the countermeasure effect of dew condensation by numerical predictions. Moreover, the prediction about pre-cooling and pre-heating effect of introduced outside air should be also carried out. The purpose of this study is to establish the design and operation method that can prevent the occurrence of dew condensation and obtain the high pre-cooling and pre-heating effect of the outside air. In this paper, we propose the evaluation method of dew condensation by the unsteady CFD analysis for the existent underground air tunnel. Moreover, we verify the technique of introducing outside air into the system considering the above two purposes of this research. We carry out the proposed CFD simulation (uncoupled simulation) coupled with humidity transport equations. After some flow fields depending on introduced outside air volume are obtained in advance for the uncoupled simulation, only temperature and humidity transport equations using these obtained flow fields are solved. Therefore, it can reduce the calculation load for the CFD analysis. The target of underground air tunnel is introduced in the existing office building located in Kitakyushu, Fukuoka, Japan. Case studies are carried out such as introducing outside air according with the schedule, implementing of the dew point temperature control depending on surface temperature of concrete and dew point temperature, or changing the introduction path of outside air. Following results were obtained; if the number of outside air intake (introduction path) was one, the pre-cooling and pre-heating effect was higher than the case of two intakes under the same air volume conditions. It was suggested that there was a possibility of dew condensation in a winter rainy day. Therefore, the restriction of the use of this system is effective as countermeasures in the rainy weather. Even if the introduction path of outside air is complicated, it can prevent to some extent occurrence of dew condensation by the dew point temperature control. Using the dew point temperature control, the pre-cooling effect in the summer was decreased about 10 to 30 percent, but the pre-heating effect in the winter was slightly decreased. Given those results, it was suggested that EAHE systems has the relationship of trade-offs between air quality of introduced outside air and the effect of energy conservation in summer. In the case of uncoupled simulation coupled with humidity transport equations, the computing time was greatly reduced. Moreover, it was possible to evaluate the property of dew condensation in the system and the annual pre-cooling and pre-heating effect in short calculation time by this simulation method.

Numerical Modeling of Polydisperse Bubbly Flows by the OpenMP Parallel Algorithm

Numerical modeling of gas and liquid flows and, in particular, multiphase mediums, is a promising direction of scientific investigations and development of industrial apparatus. Experimental approach in the field of multiphase flows is not always capable of obtaining required information about the flow structure due to the excessive amount of physical phenomena involved. Numerical simulations of real flows with inclusion of all processes and phenomena or on real-scale geometries are very resource-demanding and are not feasible on stand-alone personal working stations. Thus, applying parallelization techniques at the existing solution algorithms with the means of OpenMP library alongside with supercomputer technologies can reduce computational time and can help with simulations of complex flows on the systems with shared memory.The study presents the description of the previously developed mathematical model of polydisperse multiphase flows, numerical algorithm for the solution of governed equations of the model and description of the numerical method. Simulations by the means of the proposed algorithm were carried out for the case of polydisperse bubbly flow inside water-filled rectangular column. Results presented in the paper, which are obtained during numerical experiments carried out on the “SC Politechnichesky”, comprise of the obtained flow field and bubble distributions and of the dependencies of program working time on the amount of threads and model parameters.

Prediction of mass discharge rate in conical hoppers using elastoplastic model

Precise evaluation of mass discharge rate (MDR) in hoppers is an important topic in many industries. Facilitated by an Eulerian-formulation finite element method (FEM), this paper uses an elastoplastic model to investigate the MDR in conical hoppers and evaluates its applicability in various cases of hopper geometries and material properties. The obtained flow field complies with the scaling of outlet velocity Vy~gD0 and that of the discharge rate MDR~gD05/2 universally. The MDR is basically independent of the fill height and silo width, but a strong height dependency may emerge for very small internal friction angle of granular material, similar to the fluid-like discharging observed in previous DEM simulation. As for the material properties, the MDR is mainly controlled by the plastic parameters such as internal friction angle and dilation but is insensitive to the elastic modulus. The quantitative accuracy of the model is verified by comparing experimental measurements and discrete simulation over a wide range of hopper half angles. The existing correlations are often conditionally applicable in describing MDR – some for steep hoppers while others mainly suitable for shallow ones. An empirical correlation is formulated based on the FEM results to achieve a general applicability, which may help to improve the hopper design in practical applications. The needs for future research are also discussed.

Magnetohydrodynamic time-dependent computational natural convection flow, heat and mass transfer in inclined semi-circular enclosures

Purpose The purpose of this paper is to make a numerical analysis on unsteady analysis of natural convection heat and mass transfer to obtain flow field, temperature distribution, and concentration distribution. Design/methodology/approach A finite element method is applied to solve governing equations of natural convection in curvilinear-shaped system for different parameters as thermal Rayleigh numbers (103=RaT=106), inclination angle (0°=φ=60°) and Hartmann numbers (0=Ha=100). Findings Both magnetic field and inclination angle can be used as control parameter on heat and mass transfer. Flow strength decreases almost 100 percent between Ha=0 and Ha=100 on behalf of the higher values of thermal Rayleigh number. Originality/value The originality of this work is to application of magnetic field on time-dependent natural convection flow, heat and mass transfer for curvilinear geometry.

A Combined Numerical and Experimental Study of the 3D Tumble Structure and Piston Boundary Layer Development During the Intake Stroke of a Gasoline Engine

Due to its positive effect on flame propagation in the case of a well-defined breakdown, the formation of a large-scale tumble motion is an important goal in engine development. Cycle-to-cycle variations (CCV) in the tumble position and strength however lead to a fluctuating tumble breakdown in space and time and therefore to combustion variations, indicated by CCV of the peak pressure. This work aims at a detailed investigation of the large-scale tumble motion and its interaction with the piston boundary layer during the intake stroke in a state-of-the-art gasoline engine. To allow the validation of the flow near the piston surface obtained by simulation, a new measurement technique called “Flying PIV” is applied. A detailed comparison between experimental and simulation results is carried out as well as an analysis of the obtained flow field. The large-scale tumble motion is investigated based on numerical data of multiple highly resolved intake strokes obtained using scale-resolving simulations. A method to detect the tumble center position within a 3D flow field, as an extension of previously developed 2D and 3D algorithms, is presented and applied. It is then used to investigate the phase-averaged tumble structure, its characteristics in terms of angular velocity and the CCV between the individual intake strokes. Finally, an analysis is presented of the piston boundary layer and how it is influenced by the tumble motion during the final phase of the intake stroke.

Bayesian Inference of Forces Causing Cytoplasmic Streaming in Caenorhabditis elegans Embryos and Mouse Oocytes.

Cellular structures are hydrodynamically interconnected, such that force generation in one location can move distal structures. One example of this phenomenon is cytoplasmic streaming, whereby active forces at the cell cortex induce streaming of the entire cytoplasm. However, it is not known how the spatial distribution and magnitude of these forces move distant objects within the cell. To address this issue, we developed a computational method that used cytoplasm hydrodynamics to infer the spatial distribution of shear stress at the cell cortex induced by active force generators from experimentally obtained flow field of cytoplasmic streaming. By applying this method, we determined the shear-stress distribution that quantitatively reproduces in vivo flow fields in Caenorhabditis elegans embryos and mouse oocytes during meiosis II. Shear stress in mouse oocytes were predicted to localize to a narrower cortical region than that with a high cortical flow velocity and corresponded with the localization of the cortical actin cap. The predicted patterns of pressure gradient in both species were consistent with species-specific cytoplasmic streaming functions. The shear-stress distribution inferred by our method can contribute to the characterization of active force generation driving biological streaming.

The shape and behaviour of a granular bed in a rotating drum using Eulerian flow fields obtained from PEPT

Non-invasive single-particle tracking techniques, such as positron emission particle tracking (PEPT), provide useful information about the behaviour of a representative particle moving in a bulk of similar particles in a rotating drum. The Lagrangian trajectories that they yield can be used to study, for example, particulate diffusion or granular interaction. However, often the Eulerian flow fields of the entire granular bed are more useful– they can be used to study segregation, for instance, or the evolution of the free surface of the bed. In this work, we present a technique for converting Lagrangian trajectories to Eulerian flow fields via a time-weighted residence time distribution (RTD) of the tracked particle. We then perform PEPT experiments on a mono-disperse bed of spherical particles in a cylindrical drum, rotated at various rates, and use the RTD procedure to obtain flow fields of the bed. We use these flow fields to investigate the effect of drum rotational speed on the shape and behaviour of a granular bed in a rotating drum, and the insights gained thereby to define a comprehensive set of surfaces– such as the bulk free surface– to divide the bed into regions of distinct granular behaviour. We further define scalar bed features– such as the centre of circulation of the bed– that can be used to quantitatively compare the behaviour of granular beds in rotating drums operated under various conditions.

The chromatographic performance of flow-through particles: A computational fluid dynamics study

The performance of flow-through particles has been studied by computational fluid dynamics. Computational fluid dynamics simulations was used to calculate the flow behaviour around and inside the particles rather than estimate it. The obtained flow field has been used to accurately simulate plate heights generated by flow-through particles and compare them to standard fully porous particles. The effects of particle size, particle porosity and microparticle size on the intra-particle flow and plate heights is investigated. It is shown that the intra-particle flow generates mass transfer enhancement which lowers the total plate height. An empirical model is proposed for the mass transfer enhancement and it is compared to previously proposed models. Kinetic plots are constructed for the flow-through particles. Counter-intuitively, columns packed with flow-through particles have a higher flow resistance which counters the advantages of lower plate heights. Flow-through particles offer no significant gain in kinetic performance over fully porous particles.