Physical Properties Of Flow Research Articles

Mechanism analysis of hysteretic aerodynamic characteristics on variable-sweep wings

Variable-sweep wings have large shape-changing capabilities and wide flight envelops, which are considered as one of the most promising directions for intelligent morphing UAVs. Aerodynamic investigations always focus on several static states in the varying sweep process, which ignore the unsteady aerodynamic characteristics. However, deviations to static aerodynamic forces are inevitably caused by dynamic sweep motion. In this work, first, unsteady aerodynamic characteristics on a typical variable-sweep UAV with large aspect ratio were analyzed. Then, deep mechanism of unsteady aerodynamic characteristics in the varying sweep process was studied. Finally, numerical simulation method integrated with structured moving overset grids was applied to solve the unsteady fluid of varying sweep process. The simulation results of a sweep forward-backward circle show a distinct dynamic hysteresis loop surrounding the static data for the aerodynamic forces. Compared with the static lift coefficients , at the same sweep angles, dynamic lift coefficient in sweep forward process are all smaller, while dynamic sweep backward lift coefficient are all larger. In addition, dynamic deviations to static lift coefficient are positively related with the varying sweep speeds. Mechanism study on the unsteady aerodynamic characteristics indicates that three key factors lead to the dynamic hysteresis loop in varying sweep process. They are the effects of additional velocity caused by varying sweep motion, the effects of flow hysteresis and viscosity. The additional velocity induced by sweep motion affects the transversal flow direction along the wing and the effective angle of attack at the airfoil profile. The physical properties of flow, the hysteresis and viscosity affect the unsteady aerodynamic characteristics by flow separation and induced vortexes.

High frequency Rayleigh scattering measurements of density fluctuations in high-pressure premixed combustion

Measuring physical flow properties, such as density and temperature, at high frequency in high temperature and pressure environments is very challenging. Rapid fluctuations of these properties often have an impact on combustion efficiency and stability. We hereby attempt to measure density fluctuations in high-pressure premixed combustion using high temporal resolution laser Rayleigh scattering. The Rayleigh scattering intensity was assessed by counting individual photons due to the low signal to noise ratio. The measurement system was first verified at various air pressures without combustion. Combustion experiments were then conducted at four different pressures, from 1 to 7 bar. The density fluctuations increased with pressure, but the dominant fluctuation frequency decreased. Proper orthogonal decomposition analysis of high-speed schlieren images of the flame front was used to verify the results.

Physical Survey of Thermally Heated Non-Newtonian Jeffrey Fluid in a Ciliated Conduit Having Heated Compressing and Expanding Walls

An analytical study is reported that highlights the physical aspects for a heated non-Newtonian Jeffrey liquid in a duct possessing sinusoidally moving ciliated walls. A comprehensive and specific convection analysis is conveyed for this ciliated elliptic duct problem by considering the viscous dissipation effects. The dimensional mathematical problem under consideration is transformed into its dimensionless form by means of appropriate and useful transformations. Then, velocity and temperature equations are exactly evaluated with given boundary conditions. The velocity profile is integrated over the elliptic cross-section and exact mathematical solution is obtained for the pressure gradient. Moreover, the distinct physical flow properties combined with the convection heat transfer phenomenon are discussed in detail through graphical outcomes. The illustrative streamline description shows an enhancing closed contour size with increasing Q (dimensionless flow rate).

Comparison of Flow and Solubility Properties of Mineral Trioxide Aggregate Cement with Two Additive Plasticizing Agents: An In Vitro Study

Proposition: To evaluate the physical properties of flow and solubility of pure and improved mineral trioxide aggregate (MTA) cement with the addition of two plasticizing agents: sodium ether polycarboxylate and sodium naphthalene sulfonate at three different concentrations. Material and Methods: Flow and solubility tests were carried out using the established methodology recommended by the 57 ANSI/ADA and ISO 6876:2012 standards. Pure MTA was used as control group and was compared to the MTA containing sodium ether polycarboxylate and sodium naphthalene sulfonate at concentrations of 0.5%, 1.0% and 1.5%. Data were analyzed by one-way analysis of variance followed by a post-hoc Tukey test at a 5% significance level. Results: Sodium ether polycarboxylate increased the MTA flow at the three concentrations. The flow increased with increasing concentration (P<0.05). Sodium sulfonate naphthalene also facilitated flow, though it was inferior to sodium ether polycarboxylate. Sodium naphthalene sulfonate promoted a significant increase in the solubility of MTA (p=0.000). Conclusions: The additives improved the physical properties of MTA. Sodium ether polycarboxylate was found to be superior to sodium naphthalene sulfonate at all concentrations.

Magnetohydrodynamic mixed convection during a nanofluid filled tubular enclosure

Mixed convection flow during a tubular enclosure crammed with nanofluid within the presence of a magnetic flux is numerically investigated within the present study. Rock bottom and top curved wall of the enclosure are respectively kept isothermally hot and funky while the remaining walls are insulated. The governing equations are formulated supported Boussinesq assumptions and solved with finite element method. The computation is administered for mixed convection regime and also natural convection regime with fixed values of remaining parameters. An in depth parametric discussion is presented for the physical properties of flow and temperature distributions in terms of streamlines, isotherms, average heat transfer rate within the flow domain. The results show that the flow and temperature fields suffering from varying of pertinent parameters. Moreover, heat transfer rate is increased by 139.50% with the rise in Richardson number from 0.1 to 100. The increasing rate of warmth transfer thanks to Ri is respectively decreased by 58.11% with varying of Ha from 0 to 60 and increased by 23.97% with the addition of nanoparticles up to three. Comparison is performed against the previously published results on the idea of special cases and located to be in excellent agreement.

Flow and heat transfer analysis of Eyring-Powell fluid over stratified sheet with mixed convection

This article presents the study of heat transfer under the influence of mixed convective flow of Eyring-Powell fluid over a stratified stretching sheet. The impact of heat generation/absorption is also discussed. The fluid is considered to be a viscous, incompressible, two dimensional, and laminar. Transformation, based on the similarity variables, is used for the alteration of modeled governing partial differential equations (PDEs) into ordinary differential equations (ODEs). The shooting approach is introduced to accomplish the mathematical solution of governing equations. Runge-Kutta method of order four is used for the integration purpose and Newton’s method helps to refine initial guesses. All the programming is done on MATLAB. The effects of emerging parameters on temperature and velocity profiles are discussed through graphs. The related physical properties of flow, i.e., the skin friction coefficient and Nusselt number are described graphically for various parameters. Numerical values for the Nusselt number and skin friction coefficient are tabulated for the various parameters. It is noted that increment in thermal stratification parameter yields fall in both velocity and temperature of fluid and a reverse relation is observed for the heat generation parameter.

The downhole jet pumps experimental studies efficiency improving

On the basis of the analysis of the existing criteria of hydraulic similarity, the rules of transferring the results of laboratory tests of jet pumps to the conditions of their operation in the well are considered. The geometric similarity of the flow part of the jet pump is determined by the diameters of the working nozzle, the mixing chamber and the diffuser, the lengths of the mixing chamber and the diffuser, and the distance between the working nozzle and the mixing chamber. The kinematic similarity of mixed flows is determined by the ratio of the speeds or costs of the injected and the workflows, and the dynamic one by the relative pressure in the form of the pressure ratio of the mixed, injected and workflows. To characterize the similarity of motion modes and physical properties of flows in the flowing portion of a jet pump, a Reynolds number for working, injected, and mixed flows can be used. The functional relationship between the quantities that characterize the process of mixing threads can be represented as a relationship between the similarity criteria that are made of them. The equality of any two relevant similarity criteria made up of the basic parameters and initial boundary conditions is a sufficient sign of the similarity of the two systems. A generalized Eulerian criterion is proposed for modeling a wellbore jet pump workflow that provides a relationship between geometric, kinematic, and dynamic dimensionless complexes. Due to the structural features of the ejection systems, the generalized criterion is presented in the form of a ratio of Euler criteria of mixed and working flows, the numerical values of which do not differ from the magnitude of the relative pressure of the jet pump. As a result of the conducted researches, the values ​​of dimensionless complexes are determined, which determine the conditions for transferring the results of experimental studies of the jet pump model to the real design of the well ejection system.

Magnetohydrodynamic mixed convection in a nanofluid filled tubular enclosure

Mixed convection flow in a tubular enclosure filled with nanofluid in the presence of a magnetic field is numerically investigated in the present study. The bottom and top curved wall of the enclosure are respectively kept isothermally hot and cool while the remaining walls are insulated. The governing equations are formulated based on Boussinesq assumptions and solved with finite element method. The computation is carried out for mixed convection regime (0.1 ≤ Ri ≤ 10) and also natural convection regime (10 < Ri ≤ 100) with fixed values of remaining parameters. A detailed parametric discussion is presented for the physical properties of flow and temperature distributions in terms of streamlines, isotherms, average heat transfer rate within the flow domain. The results show that the flow and temperature fields affected by varying of pertinent parameters. Moreover, heat transfer rate is increased by 139.50% with the increase in Richardson number from 0.1 to 100. The increasing rate of heat transfer due to Ri is respectively decreased by 58.11% with varying of Ha from 0 to 60 and increased by 23.97% with the addition of nanoparticles up to 3%. Comparison is performed against the previously published results on the basis of special cases and found to be in excellent agreement.

Numerical Analysis of the Physical Properties of the Flow of Molten Polymers in Grooved Profiles

There is a wide field of research on the physical properties of non-isothermal pseudoplastic fluid flow. These researches help to avoid processing failures in the fields of thermoplastics. The present work presents the effects of flow inside cavities with groove profiles. For the simulations, the Ansys fluent software was used, considering steady-state flow without incompressible fluid slip. The government equations used in the simulations were mass conservation, momentum conservation and energy conservation. In order to discretize the equations, the finite volume method was used. Similar processes are seen in the thermoplastic injection industry which justifies the intention to identify the aspects of the process which hinders thermal exchange and favors the formation of undesirable physical properties in the injected parts. The implemented viscosity model was validated with the literature and consequently allowing the application of a complete analysis of the physical properties in the flow of molten polymers.

Integrating geophysical monitoring data into multiphase fluid flow reservoir simulation

Simulation of multiphase flow systems are of critical importance in managing hydrological systems. Flow simulations are affected by a number of factors including structure and flow properties including porosity and permeability as well as the anisotropy and heterogeneity of these properties. In many cases traditional hydrological and reservoir data are highly affected by these parameters, but are not directly sensitive to them. As such modellers often adjust these parameters in an ad hoc manner until solutions numerically converge. Simulation models are generally based on structural data from reflection seismics whose physical flow properties are then populated using geostatistical extrapolation techniques utilizing a sparse number of borehole logs and core analysis. In multiphase systems including enhanced oil recovery and carbon capture and sequestration uncertainties regarding phase-dependent physical properties confounds this challenge further. Geophysical methods provide a means by which to gain an improved understanding of phase distributions in the subsurface. In this paper we will look at applications from active carbon capture and sequestration and enhanced oil recovery applications, as well as synthetic examples. Geophysical data including electromagnetic and gravity are inverted using structural constraints from the reservoir model. Inversions are then mapped into flow properties using calibrated relations such as Archie’s Equation. The coupled models can then be used to both verify and improve on the reservoir flow model which improves it’s predictive power and utility as a management tool.

Physical flow properties for Pollard-like internal water waves

We present a study of the physical flow properties for a recently derived three-dimensional nonlinear geophysical internal wave solution. The Pollard-like internal wave solution is explicit in terms of Lagrangian labelling variables, enabling us to examine the mean flow velocities and mass flux in the three-dimensional setting. We show that the Pollard-like internal water wave does not have a net wave transport.

Fluid flow and effective conductivity calculations on numerical images of bentonite microstructure

Hydraulic conductivities of compacted water-saturated bentonite were computed based on the real microstructure. The Homogenization of Periodic Media approach employed fully acknowledges the heterogeneous and multiscale microstructure of clay, as well as locally varying physical flow properties. Consequently, three levels of description were considered : the microscopic level of clay particles, the mesoscopic level of clay aggregates, mineral grains and inter-aggregate porosity, and the macroscopic level of the sample subjected to fluid pressure gradients in the laboratory. Starting from the local description of fluid flow, the expression of the effective hydraulic conductivity tensor was derived. The soft and dense gels and the open voids may form a connected flow path or remain occluded. The local problems were solved on the microstructure obtained from a digitalized micrograph by image analysis. The contribution to macroscopic flow by the soft and dense gels was investigated in various configurations, and comparisons were made with hydraulic conductivity data for MX-80 bentonite.

Chiral Separation by Flows: The Role of Flow Symmetry and Dimensionality.

Separation of enantiomers by flows is a promising chiral resolution method using cost-effective microfluidics. Notwithstanding a number of experimental and numerical studies, a fundamental understanding still remains elusive, and an important question as to whether it is possible to specify common physical properties of flows that induce separation has not been addressed. Here, we study the separation of rigid chiral objects of an arbitrary shape induced by a linear flow field at low Reynolds numbers. Based on a symmetry property under parity inversion, we show that the rate-of-strain field is essential to drift the objects in opposite directions according to chirality. From eigenmode analysis, we also derive an analytic expression for the separation conditions which shows that the flow field should be quasi-two-dimensional for the precise and efficient resolutions of microscopic enantiomers. We demonstrate this prediction by Langevin dynamics simulations with hydrodynamic interactions fully implemented. Finally, we discuss the practical feasibility of the linear flow analysis, considering separations by a vortex flow or an extensional flow under a confining potential.

Hydrodynamic focusing for microfluidic impedance cytometry: a system integration study

We present the first in-depth system integration study of in-plane hydrodynamic focusing in a microfluidic impedance cytometry lab-on-a-chip. The method relies on constricting the detection volume with non-conductive sheath flows and characterizing particles or cells based on changes in impedance. This approach represents an avenue of overcoming current limitations in sensitivity with translating cytometers to the point of care for rapid, low-cost blood analysis. While examples of integrated devices are present in the literature, no systematic study of the interplay between hydrodynamics and electrodynamics has been carried out as of yet. We develop analytical and numerical models to describe the impedimetric response of the sensor as a function of cellular characteristics, physical flow properties, and device geometry. We fabricate a working prototype lab-on-a-chip for experimental validation using latex particles. We find that ionic diffusion can be a critical limiting factor even at high Peclet number. Moreover, we explore geometric variations, revealing that the ionic diffusion-related distance between the center of the hydrodynamic focusing junction and the impedance measurement electrodes plays a dominant role. With our device, we demonstrate over fivefold enhancement in impedance signals and population separation with in-plane hydrodynamic focusing. It is only through such in-depth system studies, in both models and experiments, that optimal utilization of microsystem capabilities becomes possible.

Numerical investigation of blood flow in a deformable coronary bifurcation and non-planar branch.

Introduction: Among cardiovascular diseases, arterials stenosis is recognized more commonly than the others. Hemodynamic characteristics of blood play a key role in the incidence of stenosis. This paper numerically investigates the pulsatile blood flow in a coronary bifurcation with a non-planar branch. To create a more realistic analysis, the wall is assumed to be compliant. Furthermore, the flow is considered to be three-dimensional, incompressible, and laminar. Methods: The effects of non-Newtonian blood, compliant walls and different angles of bifurcation on hemodynamic characteristics of flow were evaluated. Shear thinning of blood was simulated with the Carreau-Yasuda model. The current research was mainly focused on the flow characteristics in bifurcations since atherosclerosis occurs mostly in bifurcations. Moreover, as the areas with low shear stresses are prone to stenosis, these areas were identified. Results: Our findings indicated that the compliant model of the wall, bifurcation’s angle, and other physical properties of flow have an impact on hemodynamics of blood flow. Lower wall shear stress was observed in the compliant wall than that in the rigid wall. The outer wall of bifurcation in all models had lower wall shear stress. In bifurcations with larger angles, wall shear stress was higher in outer walls, and lower in inner walls. Conclusion: The non-Newtonian blood vessels and different angles of bifurcation on hemodynamic characteristics of flow evaluation confirmed a lower wall shear stress in the compliant wall than that in the rigid wall, while the wall shear stress was higher in outer walls but lower in inner walls in the bifurcation regions with larger angles.

Experimental validation of numerical simulations on a cerebral aneurysm phantom model

The treatment of cerebral aneurysms, found in roughly 5% of the population and associated in case of rupture to a high mortality rate, is a major challenge for neurosurgery and neuroradiology due to the complexity of the intervention and to the resulting, high hazard ratio. Improvements are possible but require a better understanding of the associated, unsteady blood flow patterns in complex 3D geometries. It would be very useful to carry out such studies using suitable numerical models, if it is proven that they reproduce accurately enough the real conditions. This validation step is classically based on comparisons with measured data. Since in vivo measurements are extremely difficult and therefore of limited accuracy, complementary model-based investigations considering realistic configurations are essential. In the present study, simulations based on computational fluid dynamics (CFD) have been compared with in situ, laser-Doppler velocimetry (LDV) measurements in the phantom model of a cerebral aneurysm. The employed 1:1 model is made from transparent silicone. A liquid mixture composed of water, glycerin, xanthan gum and sodium chloride has been specifically adapted for the present investigation. It shows physical flow properties similar to real blood and leads to a refraction index perfectly matched to that of the silicone model, allowing accurate optical measurements of the flow velocity. For both experiments and simulations, complex pulsatile flow waveforms and flow rates were accounted for. This finally allows a direct, quantitative comparison between measurements and simulations. In this manner, the accuracy of the employed computational model can be checked.

Swimmer-tracer scattering at low Reynolds number

Understanding the stochastic dynamics of tracer particles in active fluids is important for identifying the physical properties of flow generating objects such as colloids, bacteria or algae. Here, we study both analytically and numerically the scattering of a tracer particle in different types of time-dependent, hydrodynamic flow fields. Specifically, we compare the tracer motion induced by an externally driven colloid with the one generated by various self-motile, multi-sphere swimmers. Our results suggest that force-free swimmers generically induce loop-shaped tracer trajectories. The specific topological structure of these loops is determined by the hydrodynamic properties of the microswimmer. Quantitative estimates for typical experimental conditions imply that the loops survive on average even if Brownian motion effects are taken into account.

Equation-Free/Galerkin-Free Reduced-Order Modeling of the Shallow Water Equations Based on Proper Orthogonal Decomposition

In this paper, two categories of reduced-order modeling (ROM) of the shallow water equations (SWEs) based on the proper orthogonal decomposition (POD) are presented. First, the traditional Galerkin-projection POD/ROM is applied to the one-dimensional (1D) SWEs. The result indicates that although the Galerkin-projection POD/ROM is suitable for describing the physical properties of flows (during the POD basis functions’ construction time), it cannot predict that the dynamics of the shallow water flows properly as it was expected, especially with complex initial conditions. Then, the study is extended to applying the equation-free/Galerkin-free POD/ROM to both 1D and 2D SWEs. In the equation-free/Galerkin-free framework, the numerical simulation switches between a fine-scale model, which provides data for construction of the POD basis functions, and a coarse-scale model, which is designed for the coarse-grained computational study of complex, multiscale problems like SWEs. In the present work, the Beam & Warming and semi-implicit time integration schemes are applied to the 1D and 2D SWEs, respectively, as fine-scale models and the coefficients of a few POD basis functions (reduced-order model) are considered as a coarse-scale model. Projective integration is applied to the coarse-scale model in an equation-free framework with a time step grater than the one used for a fine-scale model. It is demonstrated that equation-free/Galerkin-free POD/ROM can resolve the dynamics of the complex shallow water flows. Moreover, the computational cost of the approach is less than the one for a fine-scale model.

Evolution of coherent structures and feedback mechanism of the plane jet impinging on a small cylinder

The dynamics of coherent structures and their instability evolution of the small cylinder impinging plane jet are extensively studied in this paper. The hot-wire measurements are conducted to investigate the physical flow properties and relevant flow field behaviors. The jet exit velocity is operated between 2– 26 m/ s , with the Reynolds number range from 2.1×10 3 to 2.7×10 4 based on the initial jet width. The acoustic excitation is applied to verify the instability evolution mechanism and is introduced at the jet nozzle exit with two arrays of small loudspeakers. A modified feedback mechanism is proposed to successfully explain the interaction between the cylinder and the plane jet. The competition between the jet and wake shear layer instabilities is significantly revealed in comparison with the standing wave number measured in the self-sustained oscillating flow. The augmentation effect of acoustics excited at the resonant frequency on the impinging flow with the small cylinder is also explored in detail to substantiate the feedback mechanism.

The physical character of subaqueous sedimentary density flows and their deposits

The complexity of flow and wide variety of depositional processes operating in subaqueous density flows, combined with post‐depositional consolidation and soft‐sediment deformation, often make it difficult to interpret the characteristics of the original flow from the sedimentary record. This has led to considerable confusion of nomenclature in the literature. This paper attempts to clarify this situation by presenting a simple classification of sedimentary density flows, based on physical flow properties and grain‐support mechanisms, and briefly discusses the likely characteristics of the deposited sediments. Cohesive flows are commonly referred to as debris flows and mud flows and defined on the basis of sediment characteristics. The boundary between cohesive and non‐cohesive density flows (frictional flows) is poorly constrained, but dimensionless numbers may be of use to define flow thresholds. Frictional flows include a continuous series from sediment slides to turbidity currents. Subdivision of these flows is made on the basis of the dominant particle‐support mechanisms, which include matrix strength (in cohesive flows), buoyancy, pore pressure, grain‐to‐grain interaction (causing dispersive pressure), Reynolds stresses (turbulence) and bed support (particles moved on the stationary bed). The dominant particle‐support mechanism depends upon flow conditions, particle concentration, grain‐size distribution and particle type. In hyperconcentrated density flows, very high sediment concentrations (>25 volume%) make particle interactions of major importance. The difference between hyperconcentrated density flows and cohesive flows is that the former are friction dominated. With decreasing sediment concentration, vertical particle sorting can result from differential settling, and flows in which this can occur are termed concentrated density flows. The boundary between hyperconcentrated and concentrated density flows is defined by a change in particle behaviour, such that denser or larger grains are no longer fully supported by grain interaction, thus allowing coarse‐grain tail (or dense‐grain tail) normal grading. The concentration at which this change occurs depends on particle size, sorting, composition and relative density, so that a single threshold concentration cannot be defined. Concentrated density flows may be highly erosive and subsequently deposit complete or incomplete Lowe and Bouma sequences. Conversely, hydroplaning at the base of debris flows, and possibly also in some hyperconcentrated flows, may reduce the fluid drag, thus allowing high flow velocities while preventing large‐scale erosion. Flows with concentrations <9% by volume are true turbidity flows (sensuBagnold, 1962), in which fluid turbulence is the main particle‐support mechanism. Turbidity flows and concentrated density flows can be subdivided on the basis of flow duration into instantaneous surges, longer duration surge‐like flows and quasi‐steady currents. Flow duration is shown to control the nature of the resulting deposits. Surge‐like turbidity currents tend to produce classical Bouma sequences, whose nature at any one site depends on factors such as flow size, sediment type and proximity to source. In contrast, quasi‐steady turbidity currents, generated by hyperpycnal river effluent, can deposit coarsening‐up units capped by fining‐up units (because of waxing and waning conditions respectively) and may also include thick units of uniform character (resulting from prolonged periods of near‐steady conditions). Any flow type may progressively change character along the transport path, with transformation primarily resulting from reductions in sediment concentration through progressive entrainment of surrounding fluid and/or sediment deposition. The rate of fluid entrainment, and consequently flow transformation, is dependent on factors including slope gradient, lateral confinement, bed roughness, flow thickness and water depth. Flows with high and low sediment concentrations may co‐exist in one transport event because of downflow transformations, flow stratification or shear layer development of the mixing interface with the overlying water (mixing cloud formation). Deposits of an individual flow event at one site may therefore form from a succession of different flow types, and this introduces considerable complexity into classifying the flow event or component flow types from the deposits.