Distributions Of Fluid Research Articles

A numerical study of water entry of asymmetric wedges using a CIP-based model

The two-dimensional water entry of wedges with different inclination angles is numerically investigated using a constrained interpolation profile (CIP)-based model, which is developed on the ground of a fixed Cartesian grid and governed by the Navier-Stokes (N-S) equations. A high-order finite difference method is employed as the flow solver, where the CIP method is used to discretize the convective term. The tangent of hyperbola for interface capturing/slope weighting (THINC/SW) is adopted to capture the free surface/interface, and an immersed boundary method is applied to simulate the motion of bodies. The present numerical model involving symmetric water entry is verified in comparison with the previous numerical and experimental results in the literature. The results of the asymmetric water entry are provided in terms of the penetration depth, velocity, pile-up coefficients, impact force of wedges, and velocity and pressure distributions of fluid. Considerable attention is paid into the effects of deadrise and inclination angles. It is found that the presence of the inclination angle significantly influences both the velocity and pressure field, and further regulates the penetration depth, velocity, pile-up coefficients, and impact force on the wedge. Specifically, wedges entering into the water with small deadrise angles are found to be more sensitive to the inclination angle than those with large deadrise angle.

Scrutiny of Unsteady Flow and Heat Transfer in a Backward-Facing Step Under Pulsating Nanofluid Blowing Using the Eulerian-Eulerian Approach

AbstractIn this paper, unsteady flow and heat transfer of water flow in a backward-facing step under pulsating nanofluid blowing are studied numerically. Attention is focused to examine the impact of this type of blowing and its pertinent parameters on the heat transfer performance and to detect possible non-equilibrium between the base fluid and the nanoparticles inside the flow field. To this aim, the Eulerian-Eulerian two-phase model is adopted. This approach consists of separate equation sets for the base fluid and the nanoparticles. So, it provides details of the flow field for each of the constituents, separately. Computations are undertaken for different cases and the consequences of the frequency, amplitude, and the mean velocity of the pulsating blowing as well as the type, diameter, and the volume fraction of the nanoparticles therein on the heat transfer characteristics are analyzed. It is found that in addition to thermal conductivity of the blown nanoparticles, their penetration into the water flow is an important trait that has a momentous role on the heat transfer rate. In the current Eulerian-Eulerian simulation, temperature distributions of the base fluid and the nanoparticles are similar but the corresponding velocity fields are quite distinct. This reveals a kind of non-equilibrium between the base fluid and the nanoparticles inside the flow that invalidates equilibrium approaches (e.g., the single-phase model or the two-phase mixture model) for the description of the problem.

Static trace free Einstein equations and stellar distributions

We construct models of static spherical distributions of perfect fluid in trace--free Einstein gravity theory. The equations governing the gravitational field are equivalent to the standard Einstein's equations however, their presentation is manifestly different which motivates the question whether new information would emerge due to the nonlinearity of the field equations. The incompressible fluid assumption does not lead to the well known Schwarzschild interior metric of Einstein gravity and a term denoting the presence of a cosmological constant is present on account of the integration process. The Schwarzschild interior is regained as a special case of a richer geometry. On the other hand, when the Schwarzschild geometry is prescribed, a constant density fluid emerges consistent with the standard equations. A complete model of an isothermal fluid sphere with pressure and density obeying the inverse square law is obtained. Corrections to the model previously presented in the literature by Saslaw {\it {et al}} are exhibited. The isothermal ansatz does not yield a constant gravitational potential in general but both potentials are position dependent. Conversely, it is shown that assuming a constant $g_{rr}$ gravitational potential does not yield an isothermal fluid in general as is the case in standard general relativity. The results of the standard Einstein equations are special cases of the models reported here. Noteworthy is the fact that whereas the previously reported isothermal solution was only of cosmological interest, the solution reported herein admit compact objects by virtue of the fact that a pressure-free hypersurface exists. Finally we analyze the consequences of selecting the Finch--Skea metric as the seed solution.

On the post-linear quadrupole-quadrupole metric

The Hartle-Thorne metric defines a reliable spacetime for most astrophysical purposes, for instance simulations of slowly rotating stars. Solving the Einstein field equations, we added terms of second order in the quadrupole moment to its post-linear version in order to compare it with solutions found by Blanchet in the multi-polar post-Minkowskian framework. We first derived the extended Hartle-Thorne metric in harmonic coordinates and then showed agreement with the corresponding post-linear metric from Blanchet. We also found a coordinate transformation from the post-linear Erez-Rosen metric to our extended Hartle-Thorne spacetime. It is well known that the Hartle-Thorne solution can be smoothly matched with an interior perfect fluid solution with appropriate physical properties. A comparison among these solutions provides a validation of them. It is clear that in order to represent realistic solutions of self-gravitating (axially symmetric) matter distributions of perfect fluid, the quadrupole moment has to be included as a physical parameter.

Boundary layer flow of dusty fluid over a radiating stretching surface embedded in a thermally stratified porous medium in the presence of uniform heat source

AbstractNumerical investigation for the effect of thermal stratification on MHD flow and heat transfer of dusty fluid over a vertical stretching sheet embedded in a thermally stratified porous medium in the presence of uniform heat source and thermal radiation. The governing equations for the problem were reduced in to dimensionless ordinary differential equations using suitable similarity transformations. The transformed nonlinear ordinary differential equations are numerically solved by applying efficient RungeKutta Fehlberg-45 Method with shooting technique. The effects of various flow controlling parameters such as Prandtl number, heat source/sink parameter, fluid particle interaction parameter, heat source parameter, radiation parameter on velocity and temperature distributions of both fluid and dust phases are depicted graphically. Finally, the numerical results are compared and found to be in good agreement with previously published results under special cases. The results indicate that the fluid phase velocity is always greater than that of the particle phase and thermal stratification significantly affects the surface shear stress as well as the surface heat transfer.

Mixed convection two-phase flow of Maxwell fluid under the influence of non-linear thermal radiation, non-uniform heat source/sink and fluid-particle suspension

Abstract A detailed investigation of two-dimensional mixed convection flow of non-Newtonian fluid due to convectively heated stretching sheet in the presence of dust particles is conducted. The influence of viscous dissipation, nonlinear thermal radiation and non-uniform heat source/sink is considered in the heat transport equation. To simulate the nonlinear thermal radiation effect, the Rosseland approximation has been used. The governing equations are transformed into a set of self-similar nonlinear ordinary differential equations by means of suitable similarity transformations, which are then solved numerically by using Shooting method. The influence of pertinent parameters on the velocity and temperature distributions of both fluid and particle phases inside the boundary layer is observed and discussed in detail. Further, the features of skin friction coefficient and Nusselt number for different values of the governing parameters are also analysed and discussed. Moreover, the numerical results of present study and those existing ones are tabulated for some limiting case.

Lattice density functional theory for confined Ising fluids: comparison between different functional approximations in slit pore

ABSTRACTIn this paper, Lafuente and Cuesta's cluster density functional theory (CDFT) and lattice mean field approximation (LMFA) are formulated and compared within the framework of lattice density functional theory (LDFT). As a comparison, an LDFT based on our previous work on nonrandom correction to LMFA is also developed, where local density approximation is adopted on the correction. The numerical results of density distributions of an Ising fluid confined in a slit pore obtained from Monte Carlo simulation are used to check these functional approximations. Due to rational treatment on the coupling between site-excluding entropic effect and contact-attracting enthalpic effect by CDFT with Bethe-Peierls approximation (named as BPA-CDFT for short), the improvement of BPA-CDFT beyond LMFA is checked as expected. And it is interesting that our LDFT has a comparative accuracy with BPA-CDFT. Apparent differences between the profiles such as solvation force, excess adsorption quantity and interfacial tension from LMFA and non-LMFAs are found in our calculations. We also discuss some possible theoretical extensions of BPA-CDFT.

Velocity field characterization of Newtonian and non-Newtonian fluids in SMX mixers using PEPT

The ability to predict fluid behavior, such as velocity distribution or degree of mixing, is a critical step in designing industrial mixing processes. However, the majority of processing technologies are difficult to study using traditional approaches, due to the opacity/impermeability of the construction materials, as well as employed fluids, and geometric complexities of such systems.The current work applies a novel technique, positron emission particle tracking (PEPT), which allows for characterization of complex systems. PEPT relies on triangulation of γ-rays emitted by a radioactive tracer particle, allowing the study of geometrically complex systems regardless of the system properties. This study compares the velocity distributions of a Newtonian fluid, glycerol, and a non-Newtonian fluid, guar gum solution (0.7%, w/w), flowing through 10 elements of a DN25 SMX mixer at 300L/h.Axial velocity remained positive throughout, and no back-mixing was exhibited. The velocity components appeared to be independent of rheology, with the overall flow across 10 mixer elements resembling plug flow. Radial velocities were unimodally distributed around zero in the direction where no mixing was induced, while in the direction in which radial mixing is induced, the velocity distributions were either uni- or bimodal, depending on the geometry of the cross-section.

Concentrating Solar Thermochemical Hydrogen Production by Biomass Gasification in Supercritical Water

Abstract Solar receiver reactor is the key component of supercritical water gasification of biomass using concentrating solar energy, and itsthermal performance directly affects the thermal efficiency and biomass gasification results. The temperature distributions of solar receiver reactor and reactant fluid are presented.The results showed that direct normal solar irradiation (DNI) have prominent effect on the temperature of cavity type solar receiver reactor, thus affecting the SCWG reaction behaviors and gasification results. A series of on-sun experiments were carried out,temperature is relatively stable withDNI small fluctuations, and the nominal fluid temperatures at the outlet of reactor varied in the range 500–650oC, which could completely meet the need of the temperature for biomass gasification in supercritical water.Model compounds of biomass (ethylene glycol, ethanol,glycerin and glucose) were continuously gasified under SCW conditions to generate hydrogen-rich fuel gas in the apparatus. Gas yields, carbon gasification efficiency and the total gasification efficiency increase with increasing DNI. The range of GE and CE is 48.5-105.8%, 37.5-95.6%, respectively.Good thermal performance and gasification results show thatsolar receiver/reactor used in this study is one of the good configurations that can be used for SCWG of biomass using concentrating solar energy.

Thermal analysis of conducting dusty fluid flow in a porous medium over a stretching cylinder in the presence of non-uniform source/sink

Abstract Background The principle aim of the present investigation is to study the heat transfer analysis of steady two dimensional flow of conducting dusty fluid over a stretching cylinder immersed in a porous media under the influence of non-uniform source/sink. Methods Governing partial differential equations are reduced into coupled non-linear ordinary differential equations using suitable similarity transformations. The resulting system of equations are then solved Numerically with efficient Runge Kutta Fehlberg-45 Method. Results Graphical display of the obtained numerical solution is performed to illustrate the influence of various flow controlling parameters like curvature parameter, magnetic parameter, porous parameter, Prandtl number, heat source/sink parameter, fluid-particle interaction parameter on velocity and temperature distributions of both fluid and dust phases. The numerical results for the skin-friction coefficient and Nusselt number are also presented. Finally, the obtained numerical solutions are compared and found to be in good agreement with previously published results under special cases. Conclusion The velocity within the boundary layer in the case of cylinder is larger than the flat surface and both the magnitude of the skin friction coefficient and heat transfer rate at the surface are higher for cylinder when compared to that of flat plate.

Experimental investigation on temperature profile and pressure drop in two-phase heat exchanger for mixed refrigerant Joule–Thomson cryocooler

The heat exchanger of a mixed refrigerant Joule–Thomson (MR J–T) cryocooler forms a very important component of the cycle. The working fluid in such a heat exchanger consists of a mixture of gases which undergo condensation and boiling heat transfer simultaneously. The design of these heat exchangers, therefore, is crucial; however, heat transfer data related to such heat exchangers is not available. In the present work, temperature distributions of hot and cold fluid along the length of the helical coil heat exchanger are measured experimentally. The effect of mixture compositions on the temperature distributions in the heat exchanger is studied. The performance of the heat exchanger is analyzed in terms of overall heat transfer coefficient and the heat transfer rate. It was found that the higher values of overall heat transfer coefficient leads to decreasing cool-down time for MR J–T cryocooler. However, to achieve lower refrigeration temperatures, the greater part of the heat exchanger should experience two-phase flow and the temperature profiles should be linear. Pressure drop studies reveal that the total pressure drop for the evaporating cold stream is crucial, which strongly depends on the mixture composition and operating conditions.

Local order variations in confined hard-sphere fluids

Pair distributions of fluids confined between two surfaces at close distance are of fundamental importance for a variety of physical, chemical, and biological phenomena, such as interactions between macromolecules in solution, surface forces, and diffusion in narrow pores. However, in contrast to bulk fluids, properties of inhomogeneous fluids are seldom studied at the pair-distribution level. Motivated by recent experimental advances in determining anisotropic structure factors of confined fluids, we analyze theoretically the underlying anisotropic pair distributions of the archetypical hard-sphere fluid confined between two parallel hard surfaces using first-principles statistical mechanics of inhomogeneous fluids. For this purpose, we introduce an experimentally accessible ensemble-averaged local density correlation function and study its behavior as a function of confining slit width. Upon increasing the distance between the confining surfaces, we observe an alternating sequence of strongly anisotropic versus more isotropic local order. The latter is due to packing frustration of the spherical particles. This observation highlights the importance of studying inhomogeneous fluids at the pair-distribution level.

An evolution of adiabatic matter: a case for the quasistatic regime

We establish the connection between the standard ADM 3+1 treatment of matter with its characteristic equivalent, in the context of spherical symmetry. The flux-conservative rendition of the fluid equations are obtained. Considering adiabatic distributions of perfect fluid, we evolve the system using the so-called post-quasi-static approximation in radiation coordinates. We obtain an adiabatic matter evolution in the quasi-static regime or slow motion, which is not shear-free nor geodesic.

Study of low speed flow cytometry for diffraction imaging with different chamber and nozzle designs

Achieving effective hydrodynamic focusing and flow stability at low speed presents a challenging design task in flow cytometry for studying phenomena such as cell adhesion and diffraction imaging of cells with low-cost cameras. We have developed different designs of flow chamber and sheath nozzle to accomplish the above goal. A 3D computational model of the chambers has been established to simulate the fluid dynamics in different chamber designs and measurements have been performed to determine the velocity and size distributions of the core fluid from the nozzle. Comparison of the simulation data with experimental results shows good agreement. With the computational model significant insights were gained for optimization of the chamber design and improvement of the cell positioning accuracy for study of slow moving cells. The benefit of low flow speed has been demonstrated also by reduced blurring in the diffraction images of single cells. Based on these results, we concluded that the new designs of chamber and sheath nozzle produce stable hydrodynamic focusing of the core fluid at low speed and allow detailed study of cellular morphology under various rheological conditions using the diffraction imaging method.

Change in MRI synovitis correlates with change in pain following intra-articular steroid injection

Purpose: Synovitis is a well recognised finding in knee osteoarthritis. It can be identified on Magnetic Resonance Imaging (MRI) as synovial thickening, although injection of contrast material is required to distinguish synovial tissue from synovial fluid. The aim of this analysis was to determinewhether change in synovial tissue volume as assessed using gadolinium (Gd) enhancedMRI imaging correlates with change in knee pain following intra-articular steroid therapy. Methods: Men and women aged 40 years and older who met ACR criteria for the disease, were recruited for participation in an ongoing open label clinical trial of intra-articular steroid therapy. Subjects who took part in the study had significant knee pain and grade 2 or higher knee OA. At baseline visit they completed a questionnaire about their symptoms including KOOS pain scale (100 1⁄4 no pain to 0 1⁄4 extreme pain) and also a VAS score (0 1⁄4 no pain] to 10 1⁄4 extreme pain) for pain on a nominated activity (VASnA). They subsequently had a Gd enhanced MRI immediately prior to having an intra-articular steroid injection with repeat questionnaire and Gd-enhanced MRI scan at follow up visit to assess synovial response usually within 2 weeks after the injection. To assess synovial tissue volume, sagittal (post CE T1W Fat Suppressed images: TR 500ms, TE 17ms; FoV 15.9 x 15.9cm; slice thickness 3mm) scans were obtained. Manual segmentation of the synovial tissue layer was performed on the post contrast knee image by a single observer. Using computer image analysis we excluded cartilage within the segmented space, by thresholding in the associated sagittal (3DWATSc: TR 20ms, TE 7.7ms, FoV 15cm, 288x288) scan. The rest of the segmented space was assumed to be a mixture of fluid and synovial tissue. We calculated the proportion of synovial tissue in every voxel using P 1⁄4 (I mf) / (ms mf) truncated to [0,1], where I is the voxel intensity and mf, ms are the means of the intensity distributions of fluid and synovial tissue volume respectively. We looked at mean synovial volume before and after the steroid injection and looked at the Spearman Rank correlation coefficient between change in synovial volume and change in the level of KOOS-pain and also VASnA. Results: We analysed data from 41 patients. Their mean age was 62.4 years (SD 10.5 years), and 21 were female (51.2%). The median time between baseline and follow up scan was 9 days (IQR 7 to 14 days). The median synovial tissue volume at baseline was 7,556mm (IQR 4,670mm to 11,269 mm), and at follow up was 7,078mm (IQR 3,642mm to 8,541mm); median difference -1,007mm (95% CI -1,909mm to -320mm). Both KOOS pain (24.7pts; 95% CI 18.4 pts to 31.0 pts) and VASnA (-3.2cm; 95% CI -4.1cm to -2.2cm) improved significantly between baseline and follow up. The change in synovial tissue volume correlated with change in VASnA (rs 1⁄4 0.39; p 1⁄4 0.01) though not with KOOS-pain (rs 1⁄4 -0.11 ; p 1⁄4 0.50). Change in VASnA did not appear to correlate with synovial tissue volume at baseline (rs 1⁄4 -0.03; p1⁄40.85); nor did change in KOOS pain (rs 1⁄4 0.17; p1⁄40.30). Conclusions: Synovial tissue volume in knee osteoarthritis, assessed with Gd-enhanced MRI correlates with change in pain assessed as pain on a nominated activity, though not KOOS, in response to intra-articular steroid injection.

Effect of a two-phase wedge-sliding model on the ingredient drift of a stable mixed fluid and its computing method

A two-phase wedge-sliding model is developed based on the micro-cellular structure and minimum entropy theory of a stable system, and it is used to describe the ingredient distribution of a mixed fluid in a non-uniform stress field and to analyse its phase drift phenomenon. In the model, the drift—inhibition angle and the expansion—inhibition angle are also deduced and used as evaluating indexes to describe the drifting trend of different ingredients among the mixed fluids. For solving above two indexes of the model, a new calculation method is developed and used to compute the phase distributions of multiphase fluid at peak stress and gradient area stress, respectively. As an example, the flow process of grease in a pipe is analysed by simulation method and used to verify the validity of the model.

A preliminary design methodology for fatigue life prediction of polymer composites for tidal turbine blades

Tidal turbine blades experience significant fatigue cycles during operation and it is expected that fatigue strength will be a major consideration in their design. Glass fibre reinforced polymers are a candidate low-cost material for this application. This article presents a methodology for preliminary fatigue design of glass fibre reinforced polymer tidal turbine blades. The methodology combines: (a) a hydrodynamic model for calculation of local distributions of fluid–blade forces; (b) a finite element structural model for prediction of blade strain distributions; (c) a fatigue damage accumulation model, which incorporates mean stress effects; and (d) uniaxial fatigue testing of two candidate glass fibre reinforced polymer materials (for illustrative purposes). The methodology is applied here for the preliminary design of a three-bladed tidal turbine concept, including tower shadow effects, and comparative assessment of pitch- and stall-regulated control with respect to fatigue performance.

Reduction in synovial tissue volume following intra-articular steroid injection in knee osteoarthritis

Reduction in synovial tissue volume following intra-articular steroid injection in knee osteoarthritis

Visualization of Scraping Heat Transfer Surface and Shape of Scraper Blade

The cholesteric liquid crystal was adopted for the visualization of temperature distributions of viscous fluid about scraper blades. It was found that the scraper blades, which form a tail of scraped fluid from the horizontal wing on the rear part of the blade, bring faster uniform bulk temperature of viscous fluid by the visualization.For each of three types of scraper blades, temperatures of the viscous bulk fluid were measured by 24 Cu-Co thermocouples in the Votator-type agitated vessel with the triple helical ribbon.Heat transfer to the scraped vessel wall was investigated in very low mixing Reynolds number and it was confirmed that heat transfer coefficient was the most high value, for the scraper blade with the horizontal wing.

Does flow variance affect bedload flux when the bed is dominated by grain roughness?

Previous studies have shown that spatial variance in fluid and critical shear stress, caused by form roughness, can increase bedload flux. Others have revealed that variance in flow velocity increases with relative submergence and that bed mobility is reduced at lower submergences. The paper explores the link between these observations and addresses the following questions: is grain roughness sufficient to cause variance in fluid shear stress and an increase in bedload flux; if this variance changes with submergence, does this mean that the increase is dependent on submergence; and does this explain the change in mobility with submergence? A simple, statistical bedload model, based on spatial distributions of fluid and critical shear stress, has been used to explore these effects over a water-worked gravel deposit. Estimates of spatially distributed fluid shear stress were gained from laboratory flume measurements of near-bed flow velocity, and a distribution of critical shear stress was simulated using a discrete particle model of the sediment distribution used in the flume. The velocity data were used to describe the change in the spatial distribution of near-bed velocity with relative submergence, which allowed the effects of submergence on flux to also be considered. The main conclusions were: (i) spatial variance in fluid shear stress from grain roughness was not sufficient to have an appreciable effect on bedload flux over water-worked gravel beds with a spatial distribution of critical shear stress; (ii) spatial variance in critical shear stress, caused by grain roughness, had a much larger influence and increased bedload flux. This was a similar level of increase observed in studies for conditions where form roughness was high; (iii) spatially averaged estimates of fluid and critical shear stress should not be used to estimate bedload flux even if form roughness is low; and (iv) a rise in relative submergence increased bedload flux. This was due to changes in the spatial distribution of near-bed velocity and not due to a lowering in the local flow velocity as has been suggested by previous studies.