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This paper presents studies on low Reynolds number pulsating flow in a circular pipe. The Navier‐Stokes equations expressed in terms of primitive variables on a clustered staggered grid were solved. A block tridiagonal algorithm coupled with cyclic reduction techniques was used to reduce computation effort. The effects of frequency on the amplitude of the fluctuating axial velocity are confined mainly to the wall region. The effects due to changes in frequency parameter are insignificant near the inlet region. The amplitude of pulsating axial velocity changes from inlet to the fully developed region by about 10% whereas for the time mean velocity, the amplitude almost doubles. It was observed that flow reversal begins at the pipe inlet section when the amplitude of oscillation is equal or greater than 1.0 and in the developing region, flow reversal would occur when the amplitude factor is greater than the critical amplitude factor.

The purpose of this study is to create a mathematical model, a numerical algorithm and a computer program for studying the vibration of composite pipelines based on the theory of beams used in the oil and gas industry, agriculture and water management, housing and communal services and other areas.

A mathematical model of vibration of a viscoelastic pipeline based on the theory of beams with a pulsating fluid flowing through it was developed. Using the Bubnov-Galerkin method, based on the polynomial approximation of deflections, the problem is reduced to the study of systems of ordinary integro-differential equations, the solution of which is found by a numerical method. A computational algorithm was developed for solving problems of vibrations of composite pipelines conveying pulsating liquid.

The stability and amplitude-time characteristics of vibration of composite pipelines with a pulsating fluid flowing in it are studied for wide range of changes in the parameters of deformable systems and fluid flow. The critical velocities of fluid flow at which the viscoelastic pipe loses its rectilinear equilibrium shape are found. The effect of singularity in the kernels of heredity on the vibrations of structures with viscoelastic properties was numerically studied. It is shown that with an increase in the viscosity parameter of the pipeline material, the critical flow velocity decreases. It was determined that an increase in the value of the fluid pulsation frequency and the excitation coefficient leads to a decrease in the critical velocity of the fluid flow. It was established that an increase in the parameters of the Winkler foundation and the rigidity parameter of the continuous layer leads to an increase in the critical flow velocity.

The study of the vibration of pipelines made of composite materials is of great theoretical and applied interest. The solution to this problem is an effective application of the theory of viscoelasticity to real processes. Therefore, the methods and problems of pipeline vibrations attract much attention from researchers. This study is devoted to solving the above problems and therefore its subject is relevant. The paper considers the results of numerical simulation of the processes of vibration of a composite pipeline based on the theory of shells during the flow of a pulsating liquid through it. A mathematical model of vibration of a composite pipeline was developed. A computational algorithm was developed for solving problems of vibrations of composite pipelines conveying pulsating liquid.

The purpose of this study is to investigate the pulsating flow in a three-dimensional channel. Channel flow is laminar and turbulent. After validation, the effect of different channel cross-sectional geometries (circular, hexagonal and triangular) with the pulsating flow are investigated. For this purpose, the alumina nanofluid was considered as a working fluid with different volume percentages (0 per cent [pure water], 3 per cent and 5 per cent).

In this study, the pulsatile flow was investigated in a three-dimensional channel. Channel flow is laminar and turbulent.

The results show that the fluid temperature decreases by increasing the volume percentage of particles of Al₂O₃; this is because of the fact that the input energy through the wall boundary is a constant value and indicates that with increasing the volume percentage, the fluid can save more energy at a constant temperature. And by adding Al₂O₃ nanofluid, thermal performance improves in channels, but it should be considered that the use of nanofluid causes a pressure drop in the channel.

Alumina/water nanofluid with the pulsating flow was investigated and compared in three different cross-sectional channel geometries (circular, hexagonal and triangular). The effect of different volume percentages (0 per cent [pure water], 3 per cent and 5 per cent) of Al₂O₃ nanofluid on temperature, velocity and pressure are studied.

The purpose of this paper is to propose a prediction method of gas-liquid two-phase flow patterns and reveal the flow characteristics in the suction chamber of a centrifugal pump.

A transparent model pump was experimentally studied, and the gas-liquid two-phase flow in the pump was numerically simulated based on the Eulerian–Eulerian heterogeneous flow model. The numerical simulation method was verified from three aspects: the flow pattern in the suction chamber, the gas spiral length and the external characteristics of the pump. The two-phase flow in the suction chamber was studied in detail by using the numerical simulation method.

There are up to eight flow patterns in the suction chamber. However, at a certain rotational speed, only six flow patterns are observed at the most. At some rotational speeds, only four flow patterns appear. The gas spiral length has little relationship with the gas flow rate. It decreases with the increase of the liquid flow rate and increases with the increase of the rotational speed. The spiral flow greatly increases the turbulence intensity in the suction chamber.

A method for predicting the flow pattern was proposed. Eight flow patterns in the suction chamber were identified. The mechanism of gas-liquid two-phase flow in the suction chamber was revealed. The research results have reference values for the stable operation of two-phase flow pumps and the optimization of suction chambers.

A numerical investigation aimed at understanding the flow and heat transfer characteristics of pulsating turbulent flow in an abrupt pipe expansion was carried out. The flow patterns are classified by four parameters; the Reynolds number, the Prandtl number, the abrupt expansion ratio and the pulsation frequency. The influence of these parameters on the flow was studied in the range 10⁴<Re<5×10⁴, 0.7<Pr<7.0, 0.2<d/D<0.6 and 5<f<35. It was found that the influence of pulsation on the mean time‐averaged Nusselt number is insignificant (around 10 per cent increase) for fluids having a Prandtl number less than unity. This effect is appreciable (around 30 per cent increase) for fluids having Prandtl number greater than unity. For all pulsation frequencies, the variation in the mean time‐averaged Nusselt number, maximum Nusselt number and its location with Reynolds number and diameter ratio exhibit similar characteristics to steady flows.

The purpose of this study is to investigate the coherent structures of pulsed opposing jets by large eddy simulation (LES) model and proper orthogonal decomposition (POD) snapshot method. Flow pulsation as an active flow control method is considered for the enhancement of transport phenomena in impinging jets. The effect of flow pulsation parameters such as pulsation signal shape and frequency on the vortical coherent structures, the energy content of primary modes and their variation are studied numerically.

In this study, flow field of turbulent pulsating opposing jets has been simulated using LES. The result of the simulation in different time steps (snapshots) are stored and POD is applied on the snapshots. In this study, the POD method and calculation of spatial modes has been done using OpenFOAM, and time coefficients have been calculated using a MATLAB code.

The results of this study show that the flow excitation has a great effect on the coherent structure formation and the energy containment of fundamental modes of the flow. When the flow was excited by a harmonic sinusoidal or step function, the turbulent kinetic energy accumulated in the set of primary modes. On the other hand, the pulsed opposing jets had more regularity compared to the steady jets. The shapes, patterns and energy values of dominant modes depended on the inlet pulsation signal. An increase in pulsation frequency leads to an augmentation in energy content of the primary modes.

The predictions may be extended to include various pulsation conditions such as: various amplitudes, Reynolds number and aspect ratio.

The results of this study are a valuable source of information for active control of transport phenomena in opposing jet configurations which is used in different industrial applications such as cooling, combustion, reactors, heating and drying processes.

In this study, the coherent structures and energy content of primary modes was studied for the first time by LES model and POD snapshot method and a comprehensive discussion on numerical results is provided.

This paper aims to compare the performance of flow pulsation versus flow stirring in the context of mixing of a passive scalar at moderate Reynolds numbers in confined flows. This comparison has been undertaken in two limits: diffusion can be neglected as compared to convection (very large Peclet) and diffusion and convection effects are comparable. The comparison was performed both in terms of global parameters: pumping power and mixing efficiency and local flow topology.

The study has been addressed by setting up a common conceptual three-dimensional problem that consisted of the mixing of two parallel streams in a square section channel past a square section prism. Stirring and pulsation frequencies and amplitudes were changed and combined at an inlet Reynolds number of 200. The numerical model was solved using a finite volume formulation by adapting a series of open-source OpenFOAM computational fluid dynamic (CFD) libraries. For cases with flow pulsation, the icoFoam solver for laminar incompressible transient flows was used. For cases with stirring, the icoDyMFoam solver, which uses the arbitrary Lagrangian–Eulerian method for the description of the moving dynamical mesh, was used to model the prism motion. At the local flow topology level, a new method was proposed to analyze mixing. Time evolution of folding and wrinkling of sheets made up of virtual particles that travel along streak lines was quantified by generating lower rank projections of the sheets onto the spaces spanned by the main eigenvectors of an appropriate space-temporal data decomposition.

In the limit when convection is dominant, the results showed the superior performance of stirring versus flow pulsation both in terms of mixing and required pumping power. In the cases with finite Peclet, the mixing parameters by stirring and flow pulsation were comparable, but pulsation required larger pumping power than stirring. For some precise synchronization of stirring and pulsation, the mixing parameter reached its maximum, although at the expense of higher pumping power. At the local flow topology level, the new method proposed to quantify mixing has been found to correlate well with the global mixing parameter.

A new systematic comparative study of two methods, stirring and pulsation, to achieve mixing of passive scalars in the mini scale for confined flows has been presented. The main value, apart from the conclusions, is that both methods have been tested against the same flow configuration, which allows for a self-consistent comparison. Of particular interest is the fact that it has been found that accurate synchronization of both methods yields mixing parameters higher than those associated to both methods taken separately. This suggests that it is possible to synchronize mixing methods of a different nature to achieve optimum designs. The new theoretical method that has been proposed to understand the mixing performance at the local level has shown promising results, and it is the intention of the authors to test its validity in a broader range of flow parameters. All these findings could be taken as potential guidelines for the design of mixing processes in the mini scale in the process industry.

The purpose of this paper is to present a numerical investigation on pulsating heat pipe (PHP) to study the slug velocities as a function of various parameters.

The governing equation of PHP is solved using explicit embedded Runge‐Kutta method, the Dormand–Prince pair in conjunction with MATLAB with the nomenclature 45 for the determination of displacement and the velocity of the slug.

The results show that lower fill ratio, higher diameter, higher operating temperature and higher temperature difference between evaporator and condenser for a given working fluid results in higher slug velocities, indicating higher momentum transfer and hence better heat transport.

Under steady state conditions, the design of a PHP is facilitated through the introduction of non‐dimensional numbers.

The displacement and slug velocities for additional working fluids, namely ethanol and methanol, are determined for the first time. The behaviour of non‐dimensional numbers, i.e. Poiseuille number, capillary number and Eckert number in a PHP as a function of various parameters have been studied for the first time.

THE greater part of the development of the components of a complicated mechanism, such as an aircraft engine, can with advantage be done apart from the mechanism as a whole. The study of any part can be more complete and improvements in operation effected more readily when it is not necessary to keep the whole working. A carburettor is in many respects a complete unit whose action may be studied with advantage apart from the engine with which it will be used. While the ultimate criterion of the performance of a carburettor is its behaviour on an engine, a great deal can be learned from suitable bench tests in which the engine is replaced by a suction plant; more use could be made of such testing methods than is done at present.

THE past two years have seen a notable increase in the number of services on aircraft for which some form of power is required. First, retractable undercarriages, followed by wing flaps, gun turrets, and automatic pilots, have demanded a light and compact source of power, capable of being transmitted to remote points on the machine. As suitable power units have become available, so have other applications presented themselves, with the consequent freeing of the pilot and crew from irksome manual effort.