A qualitative study on the pulsatile flow phenomenon in a dense fly ash pneumatic conveyor

Understanding of the dynamic particulate flow structures within a dense gas-fly ash pneumatic conveyor must be improved in order to better aid its design guidance.The complex pulsatile movement of the gas-fly ash mixture dominates the flow performance within the pipeline,and historically,non-invasive measurement devices such as the electrical capacitance tomography（ECT） were often used to sufficiently capture the flow dynamics.However,inadequate studies have been conducted on the pulsatile flow phenomenon,which directly relate to the gas-fly ash two-phase flow performance.This paper aims to investigate the pulsatile flows using an ECT device.Initially,pulsatile flow patterns under various experimental conditions were obtained through ECT.Pulses within a flow were then characterised into pulse growth and decay segments,which represent the superficial fluidisation and deaeration processes during conveying.Subsequently,structural and statistical analyses were performed on the pulse growth and decay segments.Results suggested that the increasing air mass flow rate led to the decrease of the superficial fluidisation/deaeration magnitude,however,the increase of the superficial fluidisation/deaeration durations.Also,the air mass flow rate was indicated as the dominant factor in determining the pulsing statistical parameters.This research provides fundamental insights for further modelling the dense fly ash pneumatic flows.     

Unified analysis of liquefaction and the ground flow phenomenon

Loose saturated sand behaves as a solid before liquefaction but as a fluid when the excess pore water pressure equals the initial confining stress, after which it recovers its strength. A simple constitutive equation for loose saturated sand was developed to express the phase transformation between a solid and fluid during liquefaction and the ground flow phenomenon. This constitutive equation was used for a shaking table test, and its applicability was investigated by comparing numerical and experimental results Published in Prikladnaya Mekhanika, Vol. 43, No. 8, pp. 129–144, August 2007. An erratum to this article is available at .     

Flopping phenomenon of flow behind two plates placed side-by-side normal to the flow direction

Experiments were made for the flow over two side-by-side normal plates for which the gap ratios are in the range 1.4–2.1 and the Teynolds numbers are at 6.6 × 10³ and 1.8 × 10⁴. At low gap ratios, i.e., 1.4–1.6. the gap flow appears always to be biased and flip-flops to the preferred side non-periodically with respect to time. As the gap ratio becomes larger, the percentage of time occupied by the gap flow in the biased state decreases and the non-biased state of the gap flow becomes prevalent. A comparison of the experimental results obtained under five free stream turbulence conditions further shows that the addition of artificial disturbance into the free stream promotes gap flow flopping at low gap ratios.     

The blood flow and the motion of vessel wall

The correlation problem between the blood flow and the motion of vessel wall in the mammalian circulatory system is discussed in this paper. Supposing the blood flow is under the stable oscillatory condition, a set of formulas for velocity distribution, pressure distribution, displacement of vessel wall and constraining stress are obtained. Kuchar’s formulas are extended from steady flow to unsteady oscillatory flow by means of the formulas obtained in this paper. The problem of elasticity effect of vessel wall is also discussed.     

Elasto-plastic approach for paper cockling phenomenon: On the importance of moisture gradient

Cockling of paper is a common problem occurring in the production, storage and end-use of paper. It is usually induced by a moisture content change. In many cases, cockling is an irreversible phenomenon; i.e. the initial shape is not obtained although the initial moisture content is restored. This kind of moisture content change occurs in copying machines and in the printing process, for example. In this paper, we present a continuum mechanical model, which is used to study the irreversible cockling of paper. In the model, paper is treated as an orthotropic elasto-plastic material and the model takes into account the small-scale variation of fibre orientation. The model is used to show the importance of the through-thickness moisture gradient on the cockling phenomenon during a cyclic moisture content change. The results suggest that the moisture gradient is a crucial factor for the irreversible cockling.     

Hysteresis phenomenon in supersonic flow past a system of cylinders

The interaction between the bow shocks ahead of a system of bodies in a supersonic flow is numerically investigated. Flow past cylinders with parallel axes lying in the plane perpendicular to the flow direction is calculated. Three different shock interaction patterns are obtained in modeling flow past an infinite periodic lattice, namely, the regular and Mach-type regimes and a regime with flow choking. In the case of two bodies a collective bow shock is formed. Transition between the flow patterns with variation in the freestream Mach number and the spacing between the cylinders is studied. Regular-to-Mach-configuration transition and vice versa occurs at particular angles of inclination of the bow shock at the interaction point determined by the criterion of a maximum flow deflection angle and the von Neumann criterion, respectively.     

Some progress in the study of the water entry phenomenon

 This paper reports on progress in the study of the water entry phenomenon. First, an experiment conducted measuring the velocity of the projectile after water entry. An empirical formula was obtained describing the change of the velocity of an underwater projectile with water depth. From the formula, the velocity decay coefficient β=0.5ρ_w A _o C _d/m, was determined, where ρ_w is the water density, A _o is the projection area of the projectile, C _d is the drag coefficient and m is the mass of the projectile. A theoretical model was then presented to describe the motion of the projectile during entry. Based on the obtained value of β, when the projectile was treated equivalently as a sphere, the theoretical water depth for deep closure of the cavity was predicted. Received: 10 February 2000/Accepted: 20 July 2000     

An anomalous phenomenon occurring in the flow of viscoelastic fluids out of ducts

When viscoelastic fluids flow out from horizontal ducts many cracks and protruding ridges are formed on the jet surface. As far as the authors know, this phenomenon has not yet been reported. The occurrence of the anomalous phenomenon is not affected by inlet flow condition or duct shape.The phenomenon may be divided into three regimes, namely, a stable state, a breakage state, and a multiplication state. In the breakage state one ridge divides into two parts after its growth, and in the multiplication state a new ridge is suddenly formed at a crack point. With increasing shear rate, the flow pattern of the jet changes from the stable state to the breakage state, and then to the multiplication state.Furthermore, a recoil effect is observed. In this effect many air bubbles rush into the duct from the exit when the flow is quickly stopped.     

Numerical study of flow and heat transfer during oscillatory blood flow in diseased arteries in presence of magnetic fields

A problem motivated by the investigation of the heat and mass transfer in the unsteady magnetohydrodynamic(MHD) flow of blood through a vessel is solved numerically when the lumen of the vessel has turned into the porous structure.The time-dependent permeability and the oscillatory suction velocity are considered.The computational results are presented graphically for the velocity,the temperature,and the concentration fields for various values of skin friction coefficients,Nusselt numbers,and Sherwood numbers.The study reveals that the flow is appreciably influenced by the presence of a magnetic field and also by the value of the Grashof number.     

Application of the wavelet transform for a channel flow in a mixed convection phenomenon

The aim of this paper is to investigate laminar-turbulent transition in a mixed convection phenomenon occurring in a horizontal rectangular duct. Indeed, laminar-turbulent transition is well known in the case of forced convection but the presence of secondary flow induced by natural convection on this transition is not well highlighted. In this study, we will not be concerned by determining a critical threshold value of a Reynolds number of transition but only to estimate the degree of turbulence in the transition regime, i.e. weak turbulence in the case of a mixed convection phenomenon. This is possible thanks to the application of the wavelet transform. The calculation of the Hölder exponent, associated with the maximum value of the singularity spectrum for various experimental conditions allows the degree of turbulence to be measured. The variation of the Hölder exponent versus heat flux and Reynolds number enables us to show that there are two ways to go towards turbulence: thermal by increasing heat flux and hydrodynamic by increasing fluid velocity.     

Slip effect on the magnetohydrodynamics channel flow in the presence of the across mass transfer phenomenon

This paper deals with the slip effect on the across mass transfer (AMT) phenomenon in a three-dimensional flow of a hydromagnetic viscous fluid in a channel with a stretching lower wall. Both walls of the channel are considered to be porous so that the AMT phenomenon can be established. The governing equations are solved analytically. The accuracy of the series solution is proved by comparing the results with a numerical solution. The slip condition is observed to be helpful in reducing the viscous drag on the stretching sheet.     

Non‐Newtonian blood flow study in a model cavopulmonary vascular system

A transient haemodynamic study in a model cavopulmonary vascular system has been carried out for a typical range of parameters using a finite element‐based Navier–Stokes solver. The focus of this study is to investigate the influence of non‐Newtonian behaviour of the blood on the haemodynamic quantities, such as wall shear stress (WSS) and flow pattern. The computational fluid dynamics (CFD) model is based on an artificial compressibility characteristic‐based split (AC‐CBS) scheme, which has been adopted to solve the Navier–Stokes equations in space–time domain. A power law model has been implemented to characterize the shear thinning nature of the blood depending on the local strain rate. Using the computational model, numerical investigations have been performed for Newtonian and non‐Newtonian flows for different frequencies and input pulse forms. The haemodynamic quantities observed in total cavopulmonary connection (TCPC) for the above conditions suggest that there are considerable differences in average (about 25–40%) and peak (about 50%) WSS distributions, when the non‐Newtonian behaviour of the blood is taken into account. The lower WSS levels observed for non‐Newtonian cases point to the higher risk of lesion formation, especially at higher pulsation frequencies. A realistic pulse form is relatively safer than a sinusoidal pulse as it has more energy distributed in the higher harmonics, which results in higher average WSS values. The present study highlights the importance of including non‐Newtonian shear thinning behaviour for modelling blood flow in the vicinity of repaired arterial connections. Copyright © 2010 John Wiley & Sons, Ltd.     

Origin of the echo phenomenon upon flow reversal in low molecular weight nematic liquid crystals

We analyse the transient shear stress response in tumbling nematic liquid crystals upon flow reversal within the framework of Leslie–Ericksen theory. In particular, we focus our attention on the echo phenomenon, i.e. the progressive re-emergence, upon flow reversal, of the transient oscillations observed at the flow start-up in low molecular weight (LMW) liquid crystals. We show that it is possible to interpret this phenomenon if the director distribution that develops after start-up contains a reversible and an irreversible component. In short, the formation of an echo results from the reversible component while the irreversible component attenuates its amplitude. Within this model, the relative proportion of reversible and irreversible contributions to the total director distribution determines the magnitude of the echo and its rate of decay with the increasing of elapsed time between start-up and flow reversal. The model proposed in this paper is fully analytical; in particular, we give an analytical expression for the intensity of the echo. This model is in good agreement with published experimental data for the MSHMA/5CB nematic mixture (Gu et al. J Rheol 37:985–1001, 1993; Gu and Jamieson, Macromolecules 27:337–347, 1994). We end this paper with a brief discussion contrasting the reappearance of the oscillations in liquid crystal polymers and surfactants immediately after the flow reversal, with the observation of the echo phenomenon around t?=?2t _R in LMW liquid crystals, where t _R is the time interval between the start-up and the reversal of the flow.     

Model study of noise field in the human chest due to turbulent flow in a larger blood vessel

An acoustic generation of noise by a larger human blood vessel and noise transmission in the thorax is modelled and studied. In making this, the random statistical nature of the noise sources, the basic vessel properties and the main features of the human chest structure are taken into account. Also the effects of changes in the basic vessel parameters are considered as a first approach to study acoustic effects of a vascular stenosis. The analysis of the resultant acoustic field reveals its similarity to the acoustic fields recorded in the appropriate experiments. The variations in the basic vessel parameters are found to cause the corresponding changes in the sound level and the production of new frequency components in the acoustic power spectrum. The acoustic power from a slightly thickened vessel is shown to be approximately proportional to the fourth power of the flow Reynolds number in the originally normal vessel and the eighth power of the ratio of the vessel diameters.