Effect Of External Flow Research Articles

Irreversibility estimation in triply stratified bio-marangoni convection in powell-eyring nanofluid under the influence of external flow

Due to the growing importance of bioconvection phenomena in diverse industrial processes such as oil refining, biotechnology, and food processing, it is essential to examine several effects like a chemical reaction, stratification, Marangoni convection, etc in nanofluid suspensions in the context of transport of microorganisms. The outcome of such studies may provide significant insight into controlling and as well as manipulating the transport of energy, solute, and microorganisms for achieving the requisite target. The aim of our study is to investigate the thermo-solutal Marangoni convection of gyrotactic microorganisms suspended in Powell-Eyring nanofluid in a stratified medium. This analysis also takes into account the effects of external flow and transverse magnetic field. The impact of Arrhenius activation energy, thermal radiation, and binary chemical reactions on bioconvection flow is considered under stratified Marangoni convection. Under appropriate assumptions without violating the physics, the present problem is expressed in terms of nonlinear PDEs. Some capable similarity transformations are employed to convert the PDEs into ODEs and solved numerically by the Runge-Kutta Fehlberg method. The graphical illustrations depict the effects of relevant flow parameters on temperature, nanoparticle volume fraction, and density distributions of motile microorganisms. The study focuses on understanding the variations in significant engineering quantities resulting from changes in crucial effects and analyzing irreversibilities. It is noticed that Marangoni accelerates the mass transfer process while on the other hand delaying the heat transfer and microorganisms density gradient. The dominance of Powell-Eyring nanofluid on the heat and mass transport amplified in accompanying Marangoni convection. The results indicate that the Eyring-Powell fluid significantly reduces entropy generation and the Bejan number. Conversely, an increase in entropy generation is observed for the Marangoni ratio parameter. Hence, this work provides insight into interlinked flow in bioconvective systems, with potential diverse applications in microbiological processes.

Experimental Studies on Vortex-Induced Vibration of a Piggyback Pipeline

Offshore pipelines of different diameters are often seen in piggyback arrangements in close proximity. Under the effects of external flows, the pipelines may experience vibration. Reliable prediction of the vibration amplitudes is important for the design and operation of these structures. In the present study, the effect of the position angle (α) and gap ratio (G/D) of a piggyback pipeline on the amplitude of 1DOF vortex-induced vibration (VIV) was investigated experimentally in a wind tunnel. The diameter ratio d/D of the two cylinders was 0.5. Five position angles, namely, α = 0°, 45°, 90°, 135°, and 180°, and six gap ratios at each angle, G/D = 0, 0.1, 0.2, 0.3, 0.4, 0.5, were tested. It was found that both α and G/D affected the amplitude of vibrations significantly. For all gap ratios, the amplitude of vibrations increased from α = 0° to α = 90° and then decreased to a minimum value around α = 135°. The maximum amplitude occurred around α = 90° when G/D = 0, and the minimum occurred around α = 135°, when G/D = 0.2–0.3. At other position angles, the vibration amplitude was less sensitive to G/D, especially when the latter was between 0.1 and 0.4. These results verified those obtained using numerical methods and are invaluable to engineers when designing offshore piggyback pipelines.

Numerical investigation on electrohydrodynamic conduction pumping with an external flow

As an advanced flow control and generation technology, electrohydrodynamic (EHD) pumping has received extensive attention in recent years. EHD conduction pumping is a type of EHD pumping that makes use of electric Coulomb force produced by an applied electric field and heterocharge layers formed near the electrodes in dielectric liquids. In this paper, we numerically investigated the flow characteristics of EHD conduction pumping with an external flow. A two-dimensional flushed electrode configuration with the external flow was considered. The coupled series of governing equations, which includes the charge conservation equations and the Poisson equation for the electric potential, are integrated into the finite-volume framework of the open-source OpenFOAM. The effects of external flow's strength and flow direction on the heterocharge layers and the flow field are investigated. The strength of external flow is shown by the Reynolds number varying between 0 and 40. It is found that with the strong external flow, the structure of heterocharge layers is seriously deformed toward the downstream. In addition, the maximum velocity generated in the flow field of the co-current flow is greater than that of the countercurrent flow.

Effects of Bent Outlet on Characteristics of a Fluidic Oscillator with and without External Flow

A fluidic oscillator with a bent outlet nozzle was investigated to find the effects of the bending angle on the characteristics of the oscillator with and without external flow. Unsteady aerodynamic analyses were performed on the internal flow of the oscillator with two feedback channels and the interaction between oscillator jets and external flow on a NACA0015 airfoil. The analyses were performed using three-dimensional unsteady Reynolds-averaged Navier-Stokes equations with a shear stress transport turbulence model. The bending angle was tested in a range of 0–40°. The results suggest that the jet frequency increases with the bending angle for high mass flow rates, but at a bending angle of 40°, the oscillation of the jet disappears. The pressure drop through the oscillator increases with the bending angle for positive bending angles. The external flow generally suppresses the jet oscillation, and the effect of external flow on the frequency increases as the bending angle increases. The effect of external flow on the peak velocity ratio at the exit is dominant in the cases where the jet oscillation disappears.

Effects of External Flow on Resonant Absorption of Coronal Loop Kink Oscillations Driven by an External Fast Wave: Selective Excitation Problem

Abstract Resonant absorption is considered to be a crucial mechanism for the damping of the coronal loop oscillations and plasma heating. We study resonant absorption of the coronal loop kink oscillations excited by such external drivers as flares, assuming that there is an intermediate shear flow region surrounding the loop. We find that for long coronal loops resonant absorption can be highly enhanced or reduced depending sensitively on the magnitude and direction of the flow and the spatial extent of the flow region when the transitional layer is thin. For short coronal loops, high flow speed and a thick transitional layer are needed to have a substantial resonant absorption. We provide a potential picture to explain the results where the external Alfvén speed and phase speed of the wave are important parameters. These results imply that the transport of the external wave energy into the loop is significantly changed by the shear flow region, which may cause the selective excitation of the coronal loop oscillations.

The effect of external flow on the feeding currents of sessile microorganisms.

Microscopic sessile suspension feeders live attached to surfaces and, by consuming bacteria-sized prey and by being consumed, they form an important part of aquatic ecosystems. Their environmental impact is mediated by their feeding rate, which depends on a self-generated feeding current. The feeding rate has been hypothesized to be limited by recirculating eddies that cause the organisms to feed from water that is depleted of food particles. However, those results considered organisms in still water, while ambient flow is often present in their natural habitats. We show, using a point-force model, that even very slow ambient flow, with speed several orders of magnitude less than that of the self-generated feeding current, is sufficient to disrupt the eddies around perpendicular suspension feeders, providing a constant supply of food-rich water. However, the feeding rate decreases in external flow at a range of non-perpendicular orientations due to the formation of recirculation structures not seen in still water. We quantify the feeding flow and observe such recirculation experimentally for the suspension feeder Vorticella convallaria in external flows typical of streams and rivers.

Motion of a vortex filament in an external flow

We consider a nonlinear model equation describing the motion of a vortex filament immersed in an incompressible and inviscid fluid. In the present problem setting, we also take into account the effect of external flow. We prove the unique solvability, locally in time, of an initial value problem posed on the one dimensional torus. The problem describes the motion of a closed vortex filament.

Simulation and safety analysis of the leakage of liquefied hydrogen from high-pressure container

In this paper, the leakage and diffusion of liquefied hydrogen which is stored in high-pressure container were investigated and the safety arrangement in cosmodrome focused on the effects of external flow on the above process was proposed. The phase transition process of leakage of liquefied hydrogen at the initial stage was first analyzed by considering the motion of single particle and particle group. Furthermore, the rule of leakage and diffusion of liquefied hydrogen under different conditions was thoroughly examined by CFD modelling. Through this work, the leakage pressure, leakage location, external air-flow direction and external air-flow velocity are found to have great effects on the diffusion of leaking hydrogen. By increasing the leakage pressure and putting leakage port closer to ground, the diffusion and dilution of leaking hydrogen would be strongly expedited to spread much further away. By adopting upper air blow and raising the external air speed, the concentration can be fairly reduced.

Optimal Design of Circular Baffles on Sloshing in a Rectangular Tank Horizontally Coupled by Structure

Parametric studies on the optimization of baffles on vibration suppression of partially filled tanks coupled by structure have been widely conducted in literature. However, few studies focus on the effect of the position of the baffles on fluid flow stratification and dampening the motion. In the present study, a numerical investigation, an engineering analysis, and optimal design study were performed to determine the effect of external flow on circular obstacle baffles performance on suppressing the vibrations of coupled structure in a closed basin. The single degree of freedom model (mass–spring–damper) is used to model the structure that holds the tank. The coupled system is released from an initial displacement without a velocity. The governing mass, turbulent Navier–Stokes momentum, volume of fluid, and one degree of freedom structure equations are solved by the Pressure-Implicit with Splitting of Operators algorithm in fluids and Newmark method in structure. Based on a detailed study of transient structure motion coupled with sloshing dynamics, the optimal baffle location was achieved. Optimal position of the baffle and its width are systematically obtained with reference to the quiescent free surface.

Dynamics of Deformable Active Particles under External Flow Field

In most practical situations, active particles are affected by their environment, for example, by a chemical concentration gradient, light intensity, gravity, or confinement. In particular, the effect of an external flow field is important for particles swimming in a solvent fluid. For deformable active particles such as self-propelled liquid droplets and active vesicles, as well as microorganisms such as euglenas and neutrophils, a general description has been developed by focusing on shape deformation. In this review, we present our recent studies concerning the dynamics of a single active deformable particle under an external flow field. First, a set of model equations of active deformable particles including the effect of a general external flow is introduced. Then, the dynamics under two specific flow profiles is discussed: a linear shear flow, as the simplest example, and a swirl flow. In the latter case, the scattering dynamics of the active deformable particles by the swirl flow is also considered.

Two-dimensional motion of Brownian swimmers in linear flows.

The motion of viruses and bacteria and even synthetic microswimmers can be affected by thermal fluctuations and by external flows. In this work, we study the effect of linear external flows and thermal fluctuations on the diffusion of those swimmers modeled as spherical active (self-propelled) particles moving in two dimensions. General formulae for their mean-square displacement under a general linear flow are presented. We also provide, at short and long times, explicit expressions for the mean-square displacement of a swimmer immersed in three canonical flows, namely, solid-body rotation, shear and extensional flows. These expressions can now be used to estimate the effect of external flows on the displacement of Brownian microswimmers. Finally, our theoretical results are validated by using Brownian dynamics simulations.

Investigation of Panel Flutter under the Effect of Liquid Sloshing

AbstractThis paper presents a numerical model for investigation of aeroelastic behavior of an arbitrary-shaped panel with arbitrary boundary conditions under the effect of supersonic external flow and internal liquid sloshing simultaneously. A finite-element model is used to describe the structural dynamics along with the linear piston theory for describing the supersonic external flow effects. Also a potential flow model discretized by the boundary element method is used for describing the internal flow field. Using modal analysis technique a coupled fluid-solid interaction reduced-order model is developed for the system. The developed model is used for investigation of dynamic stability boundaries of the system for different conditions of internal fluid, and new dynamic behaviors is observed in interaction of structure with internal and external flow simultaneously.

Measurement of Lipid Bilayer Viscosity by Microfluidic Shear Transmission

We use an experimental method for measuring shear transmission through an anchored hemispherical vesicle to estimate the viscosity for several different lipid membranes. We also validate predicted flow patterns and confirm a recently calculated universal ratio [1] for the flow geometry. Comparing experimental with calculated results provides insight about how membrane viscosity contributes to flow patterns in biological configurations, such as characean algae cells, where a lipid membrane experiences strong shear flow [2]. We apply a similar flow to vesicles containing an electrostatically coupled actin cortex in order to observe the effects of external flow on reorganization of proteins inside the vesicle.

Theoretical modelling of hot gas ingestion through turbine rim seals

The rim seals of gas turbines are used to prevent or reduce the ingestion of hot mainstream gas into the wheel-space between the turbine rotor and its adjacent stationary casing. The ingestion is caused by local pressure differences between the mainstream and the wheel-space; ingress usually occurs where the mainstream pressure is higher than that in the wheel-space and egress occurs where it is lower. Sealing air, which is supplied to the wheel-space, flows through the seal clearance and joins the mainstream flow. Too much sealing air is inefficient; too little can lead to disastrous consequences.The nozzle guide vanes create three-dimensional (3D) variations in the distribution of pressure in the mainstream annulus and the turbine blades create unsteady effects. Computational fluid dynamics (CFD) is both time-consuming and expensive for these 3D unsteady flows, and engine designers tend to use correlations or simple models to predict ingress. This paper describes the application of simple ‘orifice models’, the analytical solutions of which can be used to calculate the sealing effectiveness of turbine rim seals. The solutions agree well with available data for externally-induced ingress, where the effects of rotation are negligible, for rotationally-induced ingress, where the effects of the external flow are small, and for combined ingress, where the effects of both external flow and rotation are significant.

Financial flows to developing and advanced countries: determinants and implications

PurposeThe purpose of this paper is to establish a model to study the determinants of financial flows, portfolio and foreign direct investment (FDI) flows, and the impact of these determinants on economic variables in samples of developing and advanced countries. The analysis then turns to an evaluation of the effects of external flows on economic activity.Design/methodology/approachTo that end, the paper follows a two‐step procedure. First, the paper estimates a series of reduced‐form equations in differenced form, using annual data, for the current and the financial account balances as well as important underlying components, using a number of macroeconomic indicators reflecting the state of the business cycle as explanatory variables. These include not only a measure of economic growth, but also other factors that vary cyclically, such as the exchange rate and energy prices. In addition, the paper examines the effect of positive and negative shocks to these and other cyclical variables on components of the balance of payments. Second, the results are summarized in three directions. First, cross‐country correlations evaluate time‐series co‐movements between the current account balance and external flows with respect to major determinants of cyclicality across the samples of advanced and developing countries. Second, time‐series regressions evaluate the direct effects of financial flows on the current account balance within the samples of developing and advanced countries. Third, cross‐country regressions evaluate the impact of movements in trend and variability of financial flows on major economic indicators across the samples of developing and advanced countries.FindingsThe results are summarized in three directions. Across the samples of advanced and developing countries, the pervasive evidence highlights the negative correlation between the responses of the current account balance and the financial balance with respect to the various sources of cyclicality in the time‐series model. Second, using time‐series regressions the bulk of the evidence indicates that an increase in financial flows helps finance a widening current account deficit. Third, cross‐country regressions evaluate the impact of movements in trend and variability of financial flows on major economic indicators across the samples of developing and advanced countries. While FDI flows appear significant in differentiating growth performance within and across developing countries, their effects appear to be limited on growth performance in advanced countries. Portfolio flows are more relevant, compared to FDI flows, to financing a wider current account deficit, both in developing and advanced countries.Originality/valueOverall, the evidence presented in this paper establishes the importance of financial flows to external balances and macroeconomic performance within and across the samples of developing and advanced countries. In light of this evidence, macroeconomic policies should target a combination of external balances that can be easily financed by external inflows and align domestic policies to achieve the desired cyclicality in external balances, available financing, and macroeconomic performance.

Wind tunnel investigation of natural ventilation through multiple stacks. Part 1: Mean values

Wind tunnel experiments have been performed on a scale model to study unsteady natural ventilation through multiple stacks. A previously developed hot-wire technique was used to obtain both mean and instantaneous flow characteristics. The work is described in two Parts. Part 1 concentrates on the mean flows, since it is these that are usually used for design purposes. Stacks are a potential means of ensuring that the required flow pattern is obtained over a range of conditions, so that flow direction (rather than just magnitude) is an important issue. Two distinct ways in which a wind tunnel can be used for design are considered. The first is to measure surface wind pressures, from which flow directions can be inferred or calculated. The second way is to carry out direct measurements of the stack flows (magnitude and direction). Both of these ways are examined using the measured data and their advantages and disadvantages are discussed. The accuracy of the hot-wire technique was examined on the basis of the mass balance when only stacks are present. The effects of Reynolds number and wind direction on flows and pressures are presented. An investigation of the effect of opening configuration on wind pressure coefficients surprisingly revealed that in some cases the coefficients were affected. The effect of external flow on the discharge coefficients of the stacks was found to be consistent with earlier results on single stacks. There is evidence that the effect on the orifice coefficients is more important for envelope flow modeling.

Unsteady natural ventilation at model scale—Flow reversal and discharge coefficients of a short stack and an orifice

Measurements of unsteady flow rates and pressures have been made on a scale model of a building fitted with two openings—a short stack and a sharp-edged orifice. The flow reversal characteristic of the stack is found to be different to that of a longer stack tested in an earlier study. The short stack displays a greater propensity to reversal, which is consistent with its lower inertia. The time-averaged discharge coefficients of both the stack and the orifice have been examined to determine the effects of external flow. It is found that the effects are similar to those observed in an earlier study that used a different experimental approach.

Three dimensional drop tracking flow chamber for coalescence studies

We have developed a novel flow chamber which imposes a controlled axisymmetric stagnation flow to enable the study of external flow effects on coalescence dynamics. This system allows for the first time the precise positioning of a drop in a three dimensional flow and additionally enforces a highly symmetric flow around the drop. We focus on the study of a single drop approaching a stationary flat plane as this is analogous to two drops approaching each other. A single drop is created and then guided along the unsteady center line of a stagnation flow. The real time computer control algorithm analyzes video images of the drop in two orthogonal planes and manipulates flow restricting valves along the four outlets of the flow. We demonstrate using particle image velocimetry that the computer control not only controls the drop position but also ensures a symmetric flow inside the flow chamber. This chamber will enable a detailed investigation of the drainage of the thin film between the drop and the lower surface in order to probe the effect of external flow on coalescence.

External flow effects on the discharge coefficients of two types of ventilation opening

Envelope flow models are commonly used in the design of naturally ventilated buildings. Such models rely on specification of the discharge coefficient, C z , of ventilation openings, such as air vents and chimneys (stacks). Current practice is to make use of values obtained from laboratory tests under still-air conditions. These values may not be appropriate when the ventilation is due to wind, due to the external flow around the opening which is characterized by unsteadiness of both the velocity and pressure fields. Experimental tests have been carried out in a wind tunnel on two types of openings, namely a sharp-edged orifice (flush to the wall) and a long opening (chimney). Using an analytic result for the still-air case and simple dimensional analysis it is argued that the local crossflow velocity ratio, V/ u, is an important parameter for the orifice and the experimental results support this (as do some simple CFD calculations). The experimental results for the sharp-edged opening are similar to earlier work on generally larger openings. For the long opening the effects of external flow are smaller. In particular, the effects are negligible when the outlet of the opening lies in the external flow. Estimates are made of the consequential uncertainties arising in envelope flow calculations for natural ventilation design.

Stability of Lamellar Domain in Two-Dimensional Phase-Separating Binary Fluid under Poiseuille Flow

We investigate effect of external flow on domains in two-dimensional phase-separating binary fluid. By use of the coupled Cahn–Hillard and Navier–Stokes equations, we study stability of a lamellar ...