Fluid Dynamic Conditions Research Articles

Fluid–structure interaction within realistic three-dimensional models of the aneurysmatic aorta as a guidance to assess the risk of rupture of the aneurysm

Abdominal aortic aneurysm (AAA) disease is a degenerating process whose ultimate event is the rupture of the vessel wall. Rupture occurs when the stresses acting on the wall rise above the strength of the AAA wall tissue. The complex mechanical interaction between blood flow and wall dynamics in a three dimensional custom model of a patient AAA was studied by means of computational coupled fluid–structure interaction analysis. Real 3D AAA geometry is obtained from CT scans image processing. The results provide a quantitative local evaluation of the stresses due to local structural and fluid dynamic conditions. The method accounts for the complex geometry of the aneurysm, the presence of a thrombus and the interaction between solid and fluid. A proven clinical efficacy may promote the method as a tool to determine factual aneurysm risk of rupture and aid the surgeon to refer elective surgery patients.

Analysis of turbulent heat transfer from sinusoidal profile finned dissipators

In the present work the effectiveness of thermal dissipators cooled by a fluid in turbulent flow is studied by varying the fins spacing and shape. The profile of the fin is described by a sinusoidal function depending on two parameters that define its amplitude and number of oscillations. The velocity distribution in the fluid, and the temperature distribution in the dissipator and in the fluid are determined with the help of a finite element method. The model allows to study the variations of the heat transfer coefficient due to the fluid dynamic conditions imposed by the fin profile. Lastly, a combination of geometrical parameters is proposed, which yields the best dissipator performance under particular conditions.

Dynamic error correction of a thermometer for atmospheric measurements

This work deals with the dynamic correction of a thermometer for atmospheric measurements. The sensor analysed is the one launched onboard the Huygens probe of the Cassini mission. The specific aspects of the measurement are related to the strong changes in the fluid-dynamic conditions during the operative phase. This peculiarity does not allow the use of one of the various correction techniques based on the knowledge of the dynamic characteristics of the sensor. The thermometer, however, has the peculiarity of being composed of two independent platinum sensors, having very different dynamic properties. The study, starting from a previously conceived dynamic scheme of the sensor, assesses the possibility of determining continuously, from measurement data, the current values of the four time constants required for dynamic characterisation. Lastly one procedure for the dynamic correction of the measurements is presented, along with some verification of its effectiveness and, of the impact on the overall measurement uncertainty.

Influence of Fluid Dynamic Conditions on the Crystallization Kinetics of Calcium Oxalate

Influence of Fluid Dynamic Conditions on the Crystallization Kinetics of Calcium Oxalate

Treatment of aqueous effluents of the leather industry by membrane processes: A review

A general overview on the potentiality of membrane processes in the treatment of aqueous solutions coming from the leather industry is reported. The wet operations of the leather cycle which can be combined with or modified by membrane processes, such as microfiltration, ultrafiltration (UF), nanofiltration (NF) and reverse osmosis, have been described on the basis of consolidated applications and experimental tests on laboratory and industrial pilot scale. Some new applications are also proposed. The membranes and modules employed for the treatment of the effluents, pretreatment of fluids, cleaning procedures and fluid dynamic conditions in experimental applications are reported and discussed. An outline of direct and indirect energy analysis of tanning operations and the results of a mathematical model applied to the degreasing step are also presented. The integrated membrane processes described permit to rationalize the tanning cycle realizing the recovery and the recycle of several chemicals utilized in the tanneries. A reduction of environmental impact, a simplification of cleaning-up processes of wastewaters, an easy re-use of sludges, a decrease of disposal costs, a saving of chemicals and water and of direct and indirect energy are some advantages coming from the described membrane operations. In the future a wider application of the more consolidated membrane processes in this field is expected in the plant innovation phase of a tanning factory.

Mechanisms of animal navigation in odor plumes.

Chemical signals mediate many of life's processes. For organisms that use these signals to orient and navigate in their environment, where and when these cues are encountered is crucial in determining behavioral responses. In air and water, fluid mechanics impinge directly upon the distribution of odorous molecules in time and space. Animals frequently employ behavioral mechanisms that allow them to take advantage of both chemical and fluid dynamic information in order to move toward the source. In turbulent plumes, where odor is patchily distributed, animals are exposed to a highly intermittent signal. The most detailed studies that have attempted to measure fluid dynamic conditions, odor plume structure, and resultant orientation behavior have involved moths, crabs, and lobsters. The behavioral mechanisms employed by these organisms are different but generally integrate some form of chemically modulated orientation (chemotaxis) with a visual or mechanical assessment of flow conditions in order to steer up-current or upwind (rheo- or anemo-taxis, respectively). Across-stream turns are another conspicuous feature of odor-modulated tracks of a variety of organisms in different fluid conditions. In some cases, turning is initiated by detection of the lateral edges of a well-defined plume (crabs), whereas in other animals turning appears to be steered according to an internally generated program modulated by odor contacts (moth counterturning). Other organisms such as birds and fish may use similar mechanisms, but the experimental data for these organisms is not yet as convincing. The behavioral strategies employed by a variety of animals result in orientation responses that are appropriate for the dispersed, intermittent plumes dictated by the fluid-mechanical conditions in the environments that these different macroscopic organisms inhabit.

A theoretical approach for the interpretation of liquid metal surface tension measurements in the presence of oxygen

Theoretical models describing the transport of oxygen in metal/atmosphere systems under different fluid-dynamic conditions have been developed by different authors. In the present study, as in previous ones, the molecular diffusion is the process mainly controlling the exchange of matter between the liquid metal and the atmosphere. So, in this paper a diffusional model is proposed accounting for volatile oxides and for gas phase homogeneous reactions by means of two limiting conditions: instantaneous reactions and null reactions. For the boundary conditions, the model assumes a bulk flow composition of the gas layer surrounding the liquid on the upper side and a local equilibrium constraint at the liquid interface. The asymptotic behavior of the system is described, enabling the prediction of the direction of the net oxygen flux. It has been demonstrated that the results obtained are valid for any type of homogeneous gas phase reactivity, provided that no oxide fog is formed in the gas. The model is useful to correctly guide technological processes such as single crystal growth: in the paper the application to the melt silicon/oxygen system is discussed. Finally, the present model can synthesize apparently contradictory experimental measurements of surface tension available in literature into a unique portrait.

昆虫の飛行メカニズム

Flight mechanism of insect is different from that of our familiar system of aircraft, machinery, or bird. Recent studies quantitatively indicated that many features of insect flight mechanism, such as thin airfiol, high beating frequency, and continuous beating motion, well conform to the fluiddynamic condition given to the insect.

Numerical simulation of the influence of the orbiters attitude on the μg growth of InP : S crystals from an In solution during the EURECA-1 flight

S-doped InP crystals were grown from an In-solution in a THM arrangement during the EURECA-1 mission using the automatic mirror furnace (AMF) under microgravity conditions. The InP-crystals showed growth rate oscillations in the range of 0.8–2.0 μm/min with a period of 45 min, which is half the time of an orbit of the EURECA-1 satellite. The fluid dynamic conditions during this experiment are modelled using a 3D model with the commercial software FIDAP. The time-dependent simulation, considering thermal as well as solutal buoyancy effects, indicates a weak laminar flow in this material system. Due to the fixed attitude of the satellite with respect to the sun the residual gravity vector rotates relative to the sample axis. This rotation results in a significant change of the residual convection level. Its maximum is obtained, when the gravity is parallel to the growth interface (two times during each orbit). Due to a high Schmidt number Sc≈25 a time-dependent influence of the convection on the concentration field can also be observed.

Flight Mechanism of Insect. From Standpoint of View of Bio-Fluiddynamics.

Flight mechanism of insect is different from that of our familiar system of aircraft, machinery, or bird. Recent studies quantitatively indicated that many features of insect flight mechanism, such as thin airfoil, high beating frequency, or continuous beating motion, well conform to the fluiddynamic condition given to the insect.

Distinct mechanisms of platelet aggregation as a consequence of different shearing flow conditions.

Platelet aggregation contributes to arresting bleeding at wound sites, but may cause occlusion of atherosclerotic vessels, thus curtailing blood flow to vital organs. According to current dogma, the integrin alphaIIbbeta3 plays an exclusive role in linking platelets to one another through interactions with fibrinogen or vWf. We demonstrate here that, depending on shearing flow conditions, this process may require vWf binding to glycoprotein Ibalpha, even when alphaIIbbeta3 is competent to bind adhesive ligands. Platelet activation induced solely by high shear stress is initiated by glycoprotein Ibalpha interaction with vWf, but results in aggregation only if the latter can bind concurrently to alphaIIbbeta3. In contrast, platelets exposed to high shear rate after activation by exogenous agonists such as ADP and epinephrine can aggregate when fibrinogen is the alphaIIbbeta3 adhesive ligand, yet only if vWf binding to glycoprotein Ibalpha can also occur. Thus, the latter interaction appears to provide a bond with biomechanical properties necessary to overcome the effects of high shear rate and initiate interplatelet cohesion. These findings highlight the distinct function of two adhesive receptors mediating platelet aggregation under varying fluid dynamic conditions, and modify the current interpretation of a crucial event in hemostasis and thrombosis.

Endogenous nitric oxide protects against thromboembolism in venules but not in arterioles.

Because nitric oxide (NO) inhibits aggregation and adhesion of blood platelets, NO may play a role in platelet-vessel wall interactions. Therefore, the purpose of this study was to investigate the involvement of endogenous NO in thromboembolic processes, as induced by wall puncture, in rabbit mesenteric arterioles and venules (diameters 20 to 43 microm). In venules, inhibition of NO synthase by superfusion of the mesentery with N omega-nitro-L-arginine (L-NA; 0.1 mmol/L) significantly increased the duration of embolization (from 50 seconds to 511 seconds) and the number of emboli produced (from 2 to 11 emboli per vessel), while the median period of time needed to produce an embolus was not influenced. On the contrary, in arterioles, L-NA had no significant effect on embolization (duration of embolization: 426 seconds in the control and 382 seconds in the L-NA group, with 20 and 12 emboli per vessel, respectively). Addition to the L-NA superfusate of L-arginine (L-ARG; 1 mmol/L), the active precursor for endogenous NO synthesis, resulted in a complete reversal of the L-NA effects in venules, while addition of the inactive D-arginine (D-ARG; 1 mmol/L) had no effect. Addition of L-ARG and D-ARG had no significant effect in arterioles. Addition to the L-NA superfusate of the exogenous NO donor sodium nitroprusside (0.1 micromol/L) also resulted in reversal of the L-NA effects in venules, while in arterioles, it slightly but significantly decreased embolization duration. The differences in effect of L-NA on embolization between arterioles and venules were not caused by differences in fluid dynamic conditions. It is concluded that the role of endogenous NO in inhibiting thromboembolic processes is more important in venules than in arterioles.

High performance tangential flow filtration

Conventional tangential flow filtration (TFF) has traditionally been limited to separation of solutes that differ by about ten-fold in size. Wide pore-size distributions, membrane fouling, and concentration polarization phenomena have commonly been cited as reasons for this limitation. The use of TFF in the biotechnology industry has therefore been restricted to cell-protein, virus-protein, and protein-buffer separations. A multi-disciplinary team with industrial and academic members was formed to overcome these limitations and enable protein-protein separations using High Performance TFF (HPTFF) systems. Pore-size distributions have been improved with the development of new membrane formulation and casting techniques. Membrane fouling has been controlled by operating in the transmembrane pressure-dependent regime of the filtrate flux curve and by carefully controlling fluid dynamic start-up conditions. Concentration polarization was exploited to enhance, rather than limit, the resolution of solutes. Concentration polarization has also been controlled by operating a co-current filtrate stream that maintains transmembrane pressure constant along the length of the TFF module. High yields and purification factors were obtained even with small differences in protein sieving. IgG-BSA and BSA monomer-oligomer mixtures have successfully been separated with these systems. HPTFF technology provides a competitive purification tool to complement chromatographic processing of proteins.

Simulation of concentration dispersion in unsteady deflected flows

We report calculation of particle movement during oscillatory flow in flat channels containing baffles. The time history of particle positions is used to extract an averaged dispersion coefficient. We study the effect of changing the fluid dynamic conditions, channel geometry and adding a small mean flow component. The calculations are used to improve our qualitative understanding of dispersion in unsteady flows as well as quantifying dispersion in a class of practical devices.

Biofilm morphology in porous media, a study with microscopic and image techniques

Biofilm activity, behaviour and our ability to control biofilms depends to a large extent on mass transfer phenomena in the biofilm, at the biofilm-liquid interface and in the bulk liquid. Biofilms respond to changing mass transfer conditions by adjusting morphology, thereby optimising the exchange of matter with their surroundings. Observing biofilm morphology and mass transfer in relevant fluid dynamic conditions can therefore yield essential information to understand and model biofilm behaviour. Lack of such knowledge, as the case is with regards to biofilm behaviour in various porous media, such as sandstone reservoirs, limits our ability to predict biofilm effects. A transparent porous media replica of a sandstone reservoir with cybernetic image processing has been designed to study biofilm related transport phenomena in porous media. The porous medium was inoculated with a mixed bacterial culture and fed a sterile nutrient solution in a once through flow mode. The biofilm was observed by microscopy with automated image analysis. This novel integrated software/hardware cybernetic design allows near real-time, essentially simultaneous, surveillance of several critical sites in the porous network and facilitates selective recording and compilation of observations as a function of the biological activity at each particular site. Biofilm biomass distribution in space and time (morphology and morphological changes) are thereby recorded at a representative selection of sites in the porous structure. Local in-pore flow velocity measurements were carried out by measuring the velocity of suspended particulate matter such as detached cells or clusters of cells. The influence of biofilm morphology on convective mass transport could thereby be observed and recorded. This effect, on a meso scale, was also monitored by sensitive, automated pressure drop measurements across the porous medium cell. Important observations so far include: • Bioweb; the biofilm morphology in porous media is very different from the “classical film”, as it appears more like a spider web where each strand varies in size and shape. • The biofilm maintains a large surface area and minimal biofilm depth, thereby minimising mass transfer resistance between the fluid and the biofilm phase, under the conditions tested. • The biofilm influences the convective flow through pores both locally within pores and effecting the flow distribution between pores. Pores with high initial permeability thereby become less permeable, diverting more flow to less permeable zones in the porous matrix. Large variations in this picture were observed, demonstrating the need for a sophisticated experimental apparatus with high sampling capacity to investigate such an intricate system. The observed biofilm behaviour in porous media has important theoretical and practical implications. Flow diversion and permeability effects are of immediate practical importance, improving the prospects for biological treatment of reservoirs. The information obtained in this study will be applied in mathematical simulations of ground water reservoirs, bioremediation and biological enhanced oil recovery.

Quality improvement of recycled chromium in the tanning operation by membrane processes

Use of pressure-driven membrane processes integrated with conventional precipitation/dissolution operations is described in order to reduce chromium content in waste water from the tanning process and simultaneously improve the quality of the recycled chromium by means of elimination/reduction of organic lipolytic components, metals and other impurities that accompany the chromium recovered by traditional processes. The results obtained in the identification of types of membranes and modules, chemical-physical parameters, pretreatment of fluids, cleaning procedures and fluid dynamic conditions are reported and discussed. According to the obtained results, it is possible to suggest a process scheme that, starting from the exhausted chromium solution, through a nanofiltration membrane purification/concentration permits to obtain solutions that can be reused in tanning and/or retanning operations. The concentrate solution seems to guarantee improved characteristics of tanned and retanned skins with respect the skins treated with the traditional techniques as showed by chemical and physical essays on leather samples. The process permits also the reuse of the permeate from the nanofiltration in the pickling phase, considering the high content of chlorides in the solution.

Harmonic imaging with levovist

Our purpose was to test the hypothesis that second harmonic imaging preferentially detects backscatter from microbubbles compared with tissue structural components. A prototype second harmonic scanner was used to image a flow channel in a tissue-mimicking rubber phantom (liver density). Video time-intensity curves were calculated from repeated bolus injections of microbubble echocardiographic contrast material under the same fluid dynamic conditions but with three different imaging modes: (1) fundamental imaging at 2.5 MHz (transmit and receive at 2.5 MHz), (2) fun damental imaging at 5.0 MHz (transmit and receive at 5.0 MHz), and (3) second harmonic imaging (transmit at 2.5 MHz and receive at 5.0 MHz). Each video time-intensity curve was calibrated-such that quantitative backscatter intensity was measured relative to the tissue phantom (0 dB). The peak increase in backscatter from the contrast material in the channel relative to the tissue phantom and the intensity in the channel before the contrast effect (the noise floor) was measured along with the area under the calibrated time-intensity curve relative to the phantom. When referenced to the noise floor in the flow channel, all imaging modes produced approximately 25 dB of enhancement. However, when referenced to the tissue phantom, second harmonic imaging produced a 22.3 +/- 1.8 dB peak enhancement, which was greater than either fundamental imaging at 2.5 MHz (15.5 +/- 0.8 dB; p < 0.001) or fundamental imaging at 5.0 MHz (15.3 +/- 1.5 dB; p < 0.001). The area under the time-intensity curves confirmed that harmonic imaging has approximately 7 dB of relative enhancement to the phantom compared with fundamental imaging at either frequency. Second harmonic imaging specifically enhances backscatter from microbubbles compared with a tissue-mimicking phantom. This specificity for microbubbles is due to a decrease in backscatter for the tissue phantom, rather than an increase in backscatter for the microbubbles. These data support the hypothesis that second harmonic imaging may be able to detect microbubbles in the tissue vascular space by preferentially decreasing the backscatter from tissue structural components.

Mechanisms Initiating Platelet Thrombus Formation

The functions of platelets depend on their ability to interest with surface exposed at sites of tissue damage and then with one another after activation, thus aggregating into thrombi. This complex process, normally beneficial to arrest bleeding during hemostasis, may become a cause of catastrophic disease when it leads to thrombotic occlusion of atherosclerotic vessels curtailing arterial blood flow to vital organs. Fluid dynamic conditions modulate all aspects of platelet response to vascular injury. At higher levels of shear stress, encountered both in normal vessels during normal hemostasis or in pathological conditions of the vasculature during thrombosis, von Willebrand factor becomes the essential adhesive protein for both adhesion and aggregation. Two platelet membrane receptors, the glycoprotein complexes Ib-IX-V and IIb-IIIa (integrin alpha IIb beta 3), mediate the von Willebrand factor function in a coordinate and synergistic manner, each contributing unique biomechanical properties to support thrombus formation. The developing understanding of the structure and mechanism of action of the key adhesive domains of von Willebrand factor, as well as of their cognate cellular and extracellular binding sites, will provide solid pathophysiological foundation for the evaluation of novel anti-thrombotic strategies.

Biofilm morphology in porous media, a study with microscopic and image techniques

Biofilm activity, behaviour and our ability to control biofilms depends to a large extent on mass transfer phenomena in the biofilm, at the biofilm-liquid interface and in the bulk liquid. Biofilms respond to changing mass transfer conditions by adjusting morphology, thereby optimising the exchange of matter with their surroundings. Observing biofilm morphology and mass transfer in relevant fluid dynamic conditions can therefore yield essential information to understand and model biofilm behaviour. Lack of such knowledge, as the case is with regards to biofilm behaviour in various porous media, such as sandstone reservoirs, limits our ability to predict biofilm effects. A transparent porous media replica of a sandstone reservoir with cybernetic image processing has been designed to study biofilm related transport phenomena in porous media. The porous medium was inoculated with a mixed bacterial culture and fed a sterile nutrient solution in a once through flow mode. The biofilm was observed by microscopy with automated image analysis. This novel integrated software/hardware cybernetic design allows near real-time, essentially simultaneous, surveillance of several critical sites in the porous network and facilitates selective recording and compilation of observations as a function of the biological activity at each particular site. Biofilm biomass distribution in space and time (morphology and morphological changes) are thereby recorded at a representative selection of sites in the porous structure. Local in-pore flow velocity measurements were carried out by measuring the velocity of suspended particulate matter such as detached cells or clusters of cells. The influence of biofilm morphology on convective mass transport could thereby be observed and recorded. This effect, on a meso scale, was also monitored by sensitive, automated pressure drop measurements across the porous medium cell. Important observations so far include: • Bioweb ; the biofilm morphology in porous media is very different from the “classical film”, as it appears more like a spider web where each strand varies in size and shape. • The biofilm maintains a large surface area and minimal biofilm depth, thereby minimising mass transfer resistance between the fluid and the biofilm phase, under the conditions tested. • The biofilm influences the convective flow through pores both locally within pores and effecting the flow distribution between pores. Pores with high initial permeability thereby become less permeable, diverting more flow to less permeable zones in the porous matrix. Large variations in this picture were observed, demonstrating the need for a sophisticated experimental apparatus with high sampling capacity to investigate such an intricate system. The observed biofilm behaviour in porous media has important theoretical and practical implications. Flow diversion and permeability effects are of immediate practical importance, improving the prospects for biological treatment of reservoirs. The information obtained in this study will be applied in mathematical simulations of ground water reservoirs, bioremediation and biological enhanced oil recovery.

Observation of concentration dispersion in unsteady deflected flows

The aim of this paper is to investigate the dependence on fluid dynamic condition of the concentration dispersion caused by an oscillatory flow through a channel with ladder-like flow deflectors and in which vortex waves are generated by an oscillatory flow. By varying the amplitude and the frequency of the oscillation the vortex wave may be increased in strength and extended longitudinally so as to control both transverse mixing and axial transport. By directly measuring the distribution of the cross-sectional averaged concentration along the axial direction, concentration dispersion can be modelled as a diffusive process with a constant apparent diffusivity (the dispersion coefficient). This provides a global parameter to indicate the efficiency of mixing and transport. Two physical parameters, the oscillation amplitude and frequency, lead to two non-dimensional parameters, the Reynolds number, Re, and Strouhal number, St. We have presented the experimental results for different Re and St numbers and for different deflector spacing in order to show the effect of eddy motions on dispersion. We show that large dispersion enhancement is obtained when strong vortex waves are generated. Numerical experiments have been used in a parallel study and these provide a quantitative comparison for the dispersion coefficient. The results show that in addition to the controllability of dispersion, measurements for low Reynolds number flows give good agreement between numerical simulation and experimental measurement but poorer agreement for high Reynolds number flows and in channels with long ladder spacing.