Fluid Dynamic Characteristics Research Articles

Semi-computational simulation of magneto-hemodynamic flow in a semi-porous channel using optimal homotopy and differential transform methods

In this paper, the semi-numerical techniques known as the optimal homotopy analysis method (HAM) and Differential Transform Method (DTM) are applied to study the magneto-hemodynamic laminar viscous flow of a conducting physiological fluid in a semi-porous channel under a transverse magnetic field. The two-dimensional momentum conservation partial differential equations are reduced to ordinary form incorporating Lorentizian magnetohydrodynamic body force terms. These ordinary differential equations are solved by the homotopy analysis method, the differential transform method and also a numerical method (fourth-order Runge–Kutta quadrature with a shooting method), under physically realistic boundary conditions. The homotopy analysis method contains the auxiliary parameter ℏ, which provides us with a simple way to adjust and control the convergence region of solution series. The differential transform method (DTM) does not require an auxiliary parameter and is employed to compute an approximation to the solution of the system of nonlinear differential equations governing the problem. The influence of Hartmann number (Ha) and transpiration Reynolds number (mass transfer parameter, Re) on the velocity profiles in the channel are studied in detail. Interesting fluid dynamic characteristics are revealed and addressed. The HAM and DTM solutions are shown to both correlate well with numerical quadrature solutions, testifying to the accuracy of both HAM and DTM in nonlinear magneto-hemodynamics problems. Both these semi-numerical techniques hold excellent potential in modeling nonlinear viscous flows in biological systems.

Effect of Some Design Parameters on the Flow Fields and Power Consumption in a Vessel Stirred by a Rushton Turbine

Knowledge of the fluid dynamic characteristics in a stirred vessel is essential for reliable design and scale-up of a mixing system. In this paper, 3D hydrodynamics in a vessel agitated by a Rushton turbine were numerically studied (with the help of a CFD computer program (CFX 13.0)). The study was carried out covering a wide Reynolds number range: 104 - 105. Computations, based on control volume method, were made using the k-ε model. Our main purpose was to investigate the effect of vessel configuration and agitation rates on the flow structure and power consumption. Three types of vessels were used: unbaffled, baffled and a vessel with slots placed at the external perimeter of its vertical wall. The effect of slot length has been investigated. The comparison of our predicted results with available experimental data shows a satisfactory agreement.

Computational Fluid Dynamic Modeling of a Mixing Stirred Reactor: Three-Dimensional Axisymmetric Models

The fluid-dynamic characteristics of a mixing stirred reactor are studied theoretically by the computational fluid dynamic simulations in order to optimize both the hydrodynamic parameters and cell geometry. Basic fluid-dynamic three-dimensional models and operating parameters for the stirred electrolytic cell are reported. Based on the simulation results, two promising models are shown. The first one for the high cell with angular velocity of 500 for the small stirrer that is located at the distance of 0.2 from the bottom of the electrolytic cell. The second one for the small cell with angular velocity of 0.1 for the big stirrer that is located at the distance of 0.25 from the bottom of the electrolytic cell. The proposed mixing stirred reactors can be used not only for fluidization of microparticles but also for electroplating of iron particles.

Fuel reactor modelling in chemical-looping combustion of coal: 2—simulation and optimization

Chemical-looping combustion of coal (CLCC) is a promising process to carry out coal combustion with carbon capture. The process should be optimized in order to maximize the carbon capture and the combustion efficiency in the fuel reactor, which will depend on the reactor design and the operational conditions. In this work, a mathematical model of the fuel reactor is used to make predictions about the performance of the CLCC process and simulate the behaviour of the system over different operating conditions. The mathematical model considers the fluid dynamic characteristics of the fuel reactor, being a high-velocity fluidized bed reactor. It also considers the chemical processes happening inside the reactor, and the effect of a carbon separation system on the char conversion in the process.A sensitivity analysis of the effect of the efficiency of the carbon separation system, the solids inventory in the fuel reactor, the temperature in the fuel reactor, ratio of oxygen carrier to fuel, oxygen carrier reactivity, coal reactivity and coal particle on the carbon capture and combustion efficiency is carried out. Also the relevance of the water–gas shift reaction (WGS) is evaluated. The most relevant parameters affecting the carbon capture are the fuel reactor temperature and the efficiency of the carbon separation system, ηCSS. A value for ηCSS as high as 98% should be necessary to reach a carbon capture efficiency of 98.6% when the solids inventory was 1000 kg/MWth. Regarding the combustion efficiency, to use highly reactive oxygen carrier materials are desirable. In any case, additional actions or a modified design for the fuel reactor should be implemented to reach complete combustion of coal.

Dynamics of phase fronts in magmagenic fluid in the formation of gold and silver deposits in Southern Kamchatka

The origin of gold and silver deposits in the Southern Kamchatka ore district is considered in terms of a quantitative model of the dynamics of volcanogenic orthomagmatic fluid systems (VOFSs). This model takes into account structural, fluid dynamic, and thermophysical features of phase evolution in hydrothermal fluid systems differing in geometry and structural conditions of the discharge on the surfaces of volcanic edifices. It is shown that VOFSs forming sulfide-rich gold and silver deposits have no stationary impermeable caps in their discharge areas. Rather, for the most part, narrow regions of junction of phase fronts form in their interiors and migrate to the surface of volcanic edifices.Three geothermal system types are predicted by the example of plane and conical fluid conductance zones with a cap horizon: (I) where the shallow decompression boiling zone does not arise at all because of large lateral heat loss, (II) where subsurface decompression boiling zones appear at the beginning of the heat wave formation and then such a zone is practically confined to the cap rocks, and (III) where a quasistationary decompression boiling zone forms after an initial instability period or approach to a thermal equilibrium. Fluctuations or oscillations of decompression boiling zone fronts within a range of depths can exist in type III systems..

A critical comparison between local heat and mass transfer coefficients of horizontal cylinders immersed in bubbling fluidised beds

Heat and mass transfer coefficients between bubbling fluidised beds and immersed surfaces are analysed in light of recent findings that clarify the properties of the emulsion phase in proximity of immersed surfaces. The correlation between heat and mass transfer in fluidised beds is not straightforward since the two phenomena obey to different transport mechanisms, so that the classical Chilton–Colburn analogy is not valid any longer. Therefore, the link between the two phenomena can be achieved only through a deeper understanding of the fluid dynamic and morphological characteristics of the granular flow in proximity of the exchange surface. In this paper, results available in the pertinent literature are critically compared and used to provide a simple methodology to correlate the average and local heat and mass transfer coefficient with the fluid dynamic field for the case of a horizontal cylinder immersed in a bubbling fluidised bed.

Numerical simulation of a parabolic trough solar collector with nonuniform solar flux conditions by coupling FVM and MCRT method

In this paper, a more detailed three-dimensional computational model of the whole parabolic trough solar collector (PTC) system and corresponding numerical simulations by combining the Finite Volume Method (FVM) and the Monte Carlo Ray-Trace (MCRT) method were presented. Corresponding codes and solving methods were also developed and applied to simulate and analyze the total involuted photo-thermal conversion process of an experimental LS2 PTC system. The numerical results were compared with experimental data and good agreement was obtained, proving that the model and method used in the present study is feasible and reliable. More details of the characteristics of solar concentrating, solar collecting, fluid dynamics, coupled heat transfer and the whole flow and temperature fields in the receiver were also revealed and discussed. Then some typical heat transfer fluid (HTF) types and residual gas conditions were further studied. It was revealed that the properties of these HTFs/conditions and their varying relations of the fluid temperature affected the characteristics of fluid dynamics, coupled heat transfer and the whole temperature distributions in the receiver, thus affected the thermal loss and the collector efficiency synthetically.

Optimization of Parts Placement in Autoclave Processing of Composites

The main processing variable in autoclave production, besides pressure and time, is fluid temperature. The different geometry of tools and composite laminates and the fluid dynamic characteristics of each autoclave batch lead to temperature changes in the composites, during heating, soaking and cooling, not easily predicted. The soak time at maximum temperature is considered one of the most critical constraints. This time is computed for the entire autoclave batch when the last composite laminate reaches the specified cure temperature. In this work a completely different approach is presented. Areduction of cure time is achieved identifying a rule for the position of different tools inside the autoclave. An optimization model is derived by defining an objective function in terms of penalty coefficients associated to different tools and different positions into the autoclave. Test cases of the behaviour of autoclave batches have been simulated leading to significant predicted cure time reductions.

Numerical study on the propulsion of a bacterial flagellum in a viscous fluid using an immersed boundary method

The propulsion of a bacterial flagellum in a viscous fluid has gained much attention in the field of biological fluid dynamics. Inspired by the bacterial propulsion, we present a three-dimensional computational model based on an immersed boundary (IB) method to study the propulsive and fluid dynamic features of a solid flexible flagellum in a viscous fluid driven at one side by an external torque. The helical flagellum is modelled by a series of triangular cross-sections with three IB points on each cross-section. Three types of elastic links are created to connect the IB points of one cross-section to the IB points of the next cross-section to obtain an elastic network model of the flagellum. An external torque is applied at the center of the first cross-section modelled as the flagellum motor. The elastic forces are computed based on elastic energy approach and the motor forces are obtained from the magnitude and direction of the applied torque. The Stokes equations governing the flow are solved on a staggered Cartesian grid system using the fractional-step based finite-volume method. The computational model is validated by comparing the swimming speed of the flagellum obtained from the numerical results with that of the existing numerical results. The interplay of propulsive and hydrodynamic features of a left handed helical flagellum driven by an external torque is well captured using the developed model. The effect of elasticity of various types of links on the swimming speed of the flagellum is investigated. It is revealed that among the three types of elastic links, the diagonal links have dominant role in the propulsion behavior of the flagellum. The effect of pitch on the propulsion speed of the flagellum is analyzed by computing its optimum value for a constant flagellum length based on the maximum swimming speed. Numerical simulations are performed to demonstrate the forward to backward swimming behavior of the flagellum and it is concluded that the backward swimming speed is higher than the forward swimming speed. The effect of the channel wall on the forward and backward propulsion of the flagellum is examined. It is observed that the flagellum swims faster in a channel than that in an unbounded fluid domain. Further, it is found that the swimming speed of the flagellum near to a channel wall is considerably higher than that away from the walls.

The Rotor System Balance Design of Scroll Fluid Machinery

The rotor system balance design is always one of the main concerns in scroll fluid machinery dynamics, as it affects the scroll mechanical reliability, safety and life. According to the scroll fluid machinery working principle and structure, combined with the dynamic balance theory, four kinds of balance weight design philosophy were proposed in this paper and verified by a specific example, in which the bearding loads were calculated using four design methods and compared. The results show that the balance design philosophy will have a significant effect on fluid dynamic characteristics. The result is helpful for optimizing the rotor balance design of scroll fluid machinery and improving the mechanical properties.

A review of development of micro-channel heat exchanger applied in air-conditioning system

Micro-channel heat exchanger(MCHX) has been increasingly applied in HVAC&R(Heating, Ventilation, and Air Conditioning & Refrigeration) field due to its higher efficiently heat transfer rate, more compact structure, lower cost. The characteristics of micro-channel heat transfer and fluid dynamics are summarized in this paper. The methods about optimizations (ie, geometry and thermodynamic performance) and the advantages and disadvantages of the MCHX are analyzed.

An Integrated Statistical Investigation of Internal Carotid Arteries of Patients Affected by Cerebral Aneurysms

Cerebral aneurysm formation is the result of a complex interplay of systemic and local factors. Among the latter, the role of the geometry of the vessel hosting an aneurysm, of the upstream vasculature and the induced hemodynamics still need to be carefully investigated. In this paper we combine computational fluid dynamics analysis and morphological characterization and carry out the statistical investigation of the features of the internal carotid artery (ICA) of 52 patients affected by a cerebral aneurysm. The functional principal component analysis performed on the geometric and fluid dynamics features of the patients reveals correlations with the location of the aneurysm in the cerebral circulation and its rupture status. This allows a clustering of the patients that is anticipated to contribute to the design of an index for the rupture risk. In particular, ICA featuring a pronounced WSS peak are statistically inclined to hosting ruptured aneurysms. Moreover, our statistical results suggest that patients with a double-bend siphons (S-class) are less prone to the development of cerebral aneurysms.

Measurement of Fluid Dynamic Characteristics around Stenotic Obstruction in a Circular Channel

We measured experimentally the properties of fluid dynamics, velocity fields, and the pressure, around stenotic obstruction located inside a circular channel structure. Particle image velocimetry system was employed to obtain velocity fields at the central section of the circular channel in the streamwise direction. The stenosis model used was made of acrylic material with different stenotic aspect ratios. The working fluid was water and it was returned by a centrifugal pump system. Pressure measurements were carried out to validate the effect of a narrow passageway. Results showed that the acceleration of gap flow through stenotic obstruction and the pressure drop in the recirculation regime behind the stenosis model can be observed.

Fluid dynamics simulation of aqueous humour in a posterior-chamber phakic intraocular lens with a central perforation

A modified implantable collamer lens (ICL) with a central hole (diameter, 0.36 mm), a "Hole-ICL", was created to improve aqueous humour circulation. The aim of this study was to investigate the fluid dynamic characteristics of aqueous humour in a Hole-ICL using computational fluid dynamics. Fluid dynamics simulation using an ICL was performed with thermal-hydraulic analysis software FloEFD V5 (Mentor Graphics Corp.). For the simulation, three-dimensional eye models based on a modified Liou-Brennan model eye with conventional ICL (Model ICM, STAAR SURGICAL) and a Hole-ICL were used. Both ICLs were -9.0 diopters (D) and 12.0 mm in length, with an optic of 5.5 mm. The vaulting was 0.50 mm. The quantity of aqueous humour produced by the ciliary body was set at 2.80 μl/min. Flow distribution between the anterior surface of the crystalline lens and the posterior surface of the ICL was also calculated, and trajectory analysis was performed. The flow velocity 0.25 mm in front of the centre of the crystalline lens was 1.52 × 10(-1) mm/sec for the Hole-ICL and 1.21 × 10(-5) mm/sec for the conventional ICL. Outward flow from the hole in the Hole-ICL was confirmed by trajectory analysis. These results suggest that Hole-ICLs improve the circulation of aqueous humour to the anterior surface of the crystalline lens.

Numerical Study of XCP Probe's Fluid Dynamic Characteristics

Applied the finite volume method combining two-equations turbulence model,the influence of fluid dynamic characteristics on XCP probe under different factors be studied The fluid dynamic characteristics were researched under different influencing factors, such as falling speed, rotating rate,seawater density,etc. The drag coefficient under the different falling speeds and the limited velocity of submarine steady motion were obtained. Compared with the experimental results, the simulated results agree well with experimental results, the experiments have show the validity and feasibility of the numerical analysis method. These results will provide theory reference for selecting the reasonable rotating rate, analyzing stability and the movement rule of probe in the water, choosing suitable test parameters for XCP probe of different seawaters.

Vortex shedding characteristics of a circular cylinder with an oscillating wake splitter plate

The vortex shedding characteristics and the drag force acting on a circular cylinder, attached with an oscillating splitter plate, are investigated by solving the two-dimensional Navier–Stokes equations. The splitter plate is forced to exhibit harmonic oscillation about its attachment point, and the Reynolds number ( Re) of the flow is 100. In order to facilitate easy handling of the plate oscillations inside the computational domain, the equations are solved in a Cartesian grid, and the concept of immersed boundary method is used to impose the boundary conditions on the body surface. The characteristic feature of this problem is the complex interaction between the vortices shed from the splitter plate and the cylinder. Three different patterns of vortex shedding are observed in the wake of the circular cylinder depending upon the frequency and amplitude of plate oscillation: normal shedding, chain of vortices and shedding from splitter plate. It is found that the inverse relationship between the vortex formation length and Strouhal number is not applicable when the splitter plate is subjected to oscillation. Additional related interesting fluid dynamics features are also presented.

Evaluation of a numeric procedure for flow simulation of a 5 × 5 PWR rod bundle with a mixing vane spacer

The fuel assemblies of the Pressurized Water Reactors (PWR) are constituted of rod bundles arranged in a regular square configuration by spacer grids placed along its length. The presence of the spacer grids promote two antagonist effects on the core: a desirable increase of the local heat transfer downstream the grids and an adverse increase of the pressure drop due to the constriction on the coolant flow area. Most spacer grids are designed with mixing vanes which cause a cross and swirl flow between and within the subchannels, enhancing even more the heat transfer performance in the grid vicinity. The improvement of the heat transfer increases the departure from the nucleate boiling ratio, allowing higher operating power in the reactor. Due to these important thermal and fluid dynamic features, experimental and theoretical investigations have been carried out in the past years for the development of spacer grid design. More recently, the Computational Fluid Dynamics (CFD) using three dimensional Reynolds Averaged Navier Stokes (RANS) analysis has been used efficiently for this purpose. Many computational works have been performed, but the appropriate numerical procedure for the flow in rod bundle simulations is not yet a consensus. This work presents results of flow simulations performed with the commercial code CFX 11.0 in a PWR 5 × 5 rod bundle segment with a split vane spacer grid. The geometrical configuration and flow conditions used in the experimental studies performed by Karoutas et al. were assumed in the simulations. To make the simulation possible with a limited computational capacity and acceptable mesh refinement, the computational domain was divided in 7 sub-domains. The sub-domains were simulated sequentially applying the outlet results of a previous sub-domain as inlet condition for the next. In this study the k– ε turbulence model was used. The simulations were also compared with those performed by Karoutas et al. in half a subchannel and In et al. in one subchannel computational domains. Comparison between numerical and experimental results of lateral and axial velocities along of the rod bundle show good agreement for all evaluated heights downstream the spacer grid. The present numerical procedure shows better predictions than Karoutas et al. model especially further from the spacer grid where the peripheral subchannels have more influence in the average flow.

Analysis of Gas Dynamics in a Rotating Disk Cavity

A fundamental study has been performed to analysis the fluid dynamic characteristics of the gas medium in a rotating disk cavity through the commercial software CFX11.0. This paper aims to discuss the impact of the speed of rotating disk, axial and radial size and parietal lubricant film velocity and other factors on the gas flow state in cavity. Several conclusions have been obtained: the speed of rotating disk has a great impact on velocity distribution of gas flow field; the dimensionless tangential velocity of the gas medium decreases along the radial direction, and with the speed increasing, it shows a certain regularity; Dimensionless radial velocity decreases along the radial direction, and the speed of rotating disk nearly has no influence on this; The shear stress distribution along the radial direction and the distribution of tangential velocity have similar regularity; the impact of disk cavity height on the distribution of the tangential velocity along radial direction in the gas flow field is much more obvious than the impact of disk cavity width.

Exact solutions for the unsteady rotating flows of a generalized Maxwell fluid with oscillating pressure gradient between coaxial cylinders

This paper deals with the unsteady rotating flow of a generalized Maxwell fluid with fractional derivative model between two infinite straight circular cylinders, where the flow is due to an infinite straight circular cylinder rotating and oscillating pressure gradient. The velocity field and the adequate shear stress are determined by means of the combine of the sequential fractional derivatives Laplace transform and finite Hankel transform. The exact solutions are presented by integral and series form in terms of the generalized G and Mittag-Leffler functions. The similar solutions can be easily obtained for ordinary Maxwell and Newtonian fluids as limiting cases. Finally, the influence of the relaxation time and the fractional parameter on the fluid dynamic characteristics, as well as a comparison between models, is shown by graphical illustrations.

Aeroelastic Analysis of Membrane Microair Vehicles—Part I: Flutter and Limit Cycle Analysis for Fixed-Wing Configurations

This is the first of two papers concerning the fluid and structural dynamic characteristics of membrane wing microair vehicles. In this paper, a (three) batten-reinforced fixed-wing membrane microair vehicle is used to determine the effect of membrane prestrain on flutter and limit cycle behavior of fixed-wing membrane microair vehicles. For each configuration tested, flutter and subsequent limit cycle oscillations are measured in wind tunnel tests and predicted using an aeroelastic computational model consisting of a nonlinear finite element model coupled to a vortex lattice solution of the Laplace equation and boundary conditions. Agreement between the predicted and measured onset of limit cycle oscillation is good as is the prediction of the amplitude of the limit cycle at the trailing edge of the lower membrane. A direct correlation between levels of strain and the phase of the membranes during the limit cycle is found in the computation and thought to also occur in the experiment.