Squeeze flow testing of glass mat thermoplastic material

The anisotropic flow behaviour of glass fibre/polypropylene glass mat thermoplastic (GMT) has been investigated using axisymmetric squeeze flow testing between parallel circular plates. The material has a continuous swirled fibre mat construction and is manufactured by the melt-impregnation technique. Constant plate velocity squeeze flow tests have been carried out under isothermal conditions to cover a range of strain rates. Modelling of squeeze flow behaviour has been based on two simple expressions: one assumes pure shear flow during testing, while the other assumes pure biaxial extension (plug flow). The modelling results suggest that biaxial extension dominates the isothermal squeeze flow process, with apparently negligible shear flow effects.     

Numerical investigation of laminar separated flow through a channel with symmetric double expansion

Summary Two-dimensional Navier-Stokes equations have been solved numerically by a finite difference technique on a staggered grid for investigating the laminar flow of an incompressible viscous fluid through a channel with symmetric double expansion. A coordinate transformation has been employed to map the infinite irregular domain into a finite regular computational domain. At higher Reynolds numbers the flow becomes time-dependent and asymmetric. Such unsteadiness and asymmetry remains in the flow even up to turbulent flow conditions. The Pressure-Poisson equation has been solved and a pressure-velocity correction scheme has been invoked. Depending on the geometry and Reynolds number, secondary separation has been observed.     

Reorganization of the Poiseuille profile in nonisothermal flows in the reactor

The change in the temperature and velocity profile of the gas flow in a cylindrical reactor with variation in the reactor-wall temperature has numerically been investigated. It has been shown that the use of the Poiseuille profile in calculating the transient temperature profile of such a flow is quite justified. The appearance of two extrema of the radial velocity of the indicated flow on its heating (cooling) has been predicted. The maximum radial flow velocity reaches several percent of its initial average velocity.     

On the mass transfer in a sprinkled biofilter

The mass transfer from a water film to fixed fill grains (Rashig ring) has been investigated. It has been revealed that the film regime of flow is characterized by incomplete flow over the surface of Raschig rings. The mass transfer coefficient and the portion of the washed surface depending on the flow rate of water have been measured. The process of mass transfer in a freely falling film has been simulated, and a comparison between the theoretical and measured values of the mass transfer coefficient has been made.     

Supersonic flow over cylindrical afterbodies with base bleed

Computations of supersonic flow over two cylindrical afterbodies have been made using a thin-layer Navier-Stokes base flow code. The capability to compute the base flow with base bleed at supersonic speeds has been developed and used to show the effect of mass injection on the base pressure or base drag. Solutions have been obtained for a projectile and a missile configuration having cylindrical afterbodies. Numerical results show the effect of base bleed on the near wake flow field. The rise in base pressure or reduction in base drag has been clearly predicted for various mass injection rates and comparison with experimental data shows generally good agreement.     

An experimental study of rivulet flow in low-boiling liquid driven by gas flow in a minichannel

Flow regimes in a low-boiling dielectric liquid driven by gas flow in a minichannel have been experimentally studied, and a map of regimes involving 11 varieties has been constructed. It is established that a rectilinear rivulet flow is observed in a restricted range of liquid and gas flow rates.     

Three-dimensional effects of wave-like flow in horizontal pipelines

Wave-like gas-solid flow in a horizontal pipe has been investigated experimentally. The aim of the investigation was to develop a non-intrusive measuring technique for monitoring the transition from a dilute phase flow to wave-like flow and to measure the properties of wave-like flow. When a gas-solid mixture flows in a wave-like manner though the pipeline of a pneumatic conveying system the solids concentration varies, both axially and radially, with time. As a result, the pressure measured at any location will fluctuate and the difference between measuring points, both axially and radially, can be used to determine the nature of the flow. Previous workers have concentrated on individual pressure measurements and axial pressure differences. In this work the radial pressure difference has been examined. This has been compared with axial pressure measurements and those obtained using capacitance sensors. These techniques have been used to determine both wavelength and velocity. A three-dimensonal numerical model, which is based on the two-fluid theory, was also used to obtain a better understanding of the flow field characteristics.     

Laminar two-dimensional entrance region flow of power-law fluids

Summary An approximate solution for the prediction of the power-law fluid flow behaviour in the entrance region of a straight channel has been presented. This has been achieved by solving a hydrodynamically equivalent model of developing two-dimensional Newtonian flow in a channel by momentum integral method. The analysis leads to closed form expressions for the flow characteristics. A comparison of the predictions with other solutions has also been incorporated.With 3 Figures     

Influence of the Curvature of an Airfoil on the Structure of Transonic Flow

A study is made of the dependence of the pattern of transonic flow about an airfoil on the change in its shape and in the parameters of the incoming air flow. Consideration is given to a family of airfoils in a channel modeling the working section of a wind tunnel. The formation and propagation of weak shock waves in local supersonic regions near the central part of the airfoil has been investigated numerically. The finite-difference method based on a substantially nonoscillatory scheme of second order of accuracy has been employed to solve the Euler equations describing nonviscous gas flow. It has been shown that the sensitivity of the flow pattern to a change in the Mach number of the free flow substantially increases with decrease in the curvature of the airfoil.     

Investigation of a Flow around Cavities

A supersonic flow around a ring cavity on a cylindrical body has been experimentally investigated in wide ranges of relative lengths of the cavity and Mach numbers. The influence of these parameters on the pressure distribution, the structure of the flow, and the regimes of flow around the cavity has been determined.     

Electric discharge control of flow separation on oblique airfoil

The possibility of controlling flow separation on an oblique airfoil using dielectric-barrier discharge has been experimentally studied. The experiments were performed at subsonic flow velocities in a broad range of the angle of attack. The results of measurements of the velocity and surface pressure fields and an analysis of the flow patterns show that the application of electric discharge allows the interval of the angles of attack for separation-free flow past the airfoil to be significantly increased. Various discharge regimes have been studied, including those with continuous activation by single voltage pulses with a frequency of 0.5–5 kHz and by pulse trains at a repetition rate of 1–100 Hz. The efficiency of the flow separation control has been studied as dependent on the electrical parameters, frequency characteristics, and position of the discharge relative to the flow separation line.     

The Effect of Fluid Properties on Two-Phase Regimes of Flow in a Wide Rectangular Microchannel

We have experimentally studied a two-phase flow in a microchannel with a height of 150 μm and a width of 20 mm. Different liquids have been used, namely, a purified Milli-Q water, an 50% aqueous-ethanol solution, and FC-72. Before and after the experiment, the height of the microchannel was controlled, as well as the wettability of its walls and surface tension of liquids. Using the schlieren method, the main characteristics of two-phase flow in wide ranges of gas- and liquid-flow rates have been revealed. The flow regime-formation mechanism has been found to depend on the properties of the liquid used. The flow regime has been registered when the droplets moving along the microchannel are vertical liquid bridges. It has been shown that, when using FC-72 liquid, a film of liquid is formed on the upper channel wall in the whole range of gas- and liquid-flow rates.     

Simulation studies of the hydrodynamics in high-temperature solutions for crystal growth. III. flow rates in the presence of free and forced convections proceeding in opposite directions

An experimental simulation study has been carried out on the convection flow rate under the crystal during its growth from a high-temperature solution by the TSSG method or from a melt by the Czochralski method when periphery heating of the crucible is prevailing and simultaneous free and forced convections with opposite directions are present. It has been established that with increasing proportion of forced convection the resultant flow direction changes from downward to upward. Immediately before the direction change, the flow is instable with respect to time. The direction change has been found to occur at a definite ratio of the determining dimensionless numbers, which only depends on the crystal diameter. A correlation allowing determination of the flow rate in the upflow region has been obtained.     

Nonsteady flow of non-Newtonian fluids through a porous medium

In this paper, the nonsteady flow of power-law fluids with a yield stress through a porous medium is investigated. In order to illustrate the rheological behaviour effects on pressure and flow rate distributions, a flow system of practical interest was analysed. The approximate solutions in a closed form were obtained by using the integral method. For a short time, these have been formulated in terms of a moving boundary problem. The flow deviation from Newtonian behaviour was emphasized by means of several dimensionless groups. These have been found to be relevant in evaluating the rheological effects on steady and nonsteady flow behaviour through a porous medium.     

Modelling hot deformation of Inconel 718 using state variables

Abstract

A dislocation density based state variable model has been developed to describe the characteristic flow stress behaviour during hot deformation of polycrystalline superalloy Inconel 718. Model equations have been formulated to describe the role of the evolving microstructures on the macroscopic flow stress response to deformation. Following a peak in the flow stress associated with strain hardening, the model utilises mechanisms associated with dynamic recovery and recrystallisation to explain the gradual decrease in flow stress with continued deformation. Incorporation of these microstructure based state variables also enables prediction of microstructures associated with a range of hot deformation conditions. Model flow stress predictions have been validated against isothermal uniaxial compression tests conducted over a range of temperatures and strain rates relevant to industrial forging conditions.     

Rarefied gas flow through channels of finite length at various pressure ratios

A rarefied gas flow through channels (i.e. flow through parallel plates) of finite length has been modeled based on the direct simulation Monte Carlo method. The reduced flow rate and the flow field have been calculated as function of the gas rarefaction, the length-to-height ratio and the pressure ratio upstream and downstream of the channel. The whole range of the gas rarefaction including the free-molecular, transitional and hydrodynamic regimes and a wide range of the length-to-height ratio representing both short and long channels have been considered. Several values of the pressure ratio between 0 and 0.5 have been used in the calculations. It is shown that the rarefaction parameter has the most significant effect on the flow field characteristics and patterns, followed by the pressure ratio, while the length-to-height ratio has a rather modest impact. The Mach belt phenomenon is discussed in detail.     

Asymptotic analysis of the small-scale structure of the laminar boundary layer with suction

The features of the gas flow in the working section of a transonic wind tunnel have been considered. On the basis of the method of joining asymptotic expansions and the theory of detached zones mathematical models of the flow are proposed. The flow over a perforation and transverse and longitudinal slots has been investigated. In the latter case, a nonstationary and a stationary analogy with a two-dimensional flow are stated. A deflector — a new device for reflecting shocks — is proposed. The problems are discussed.     

脉冲管制冷机蓄冷器中交变流动过程理论分析

建立了交变流动蓄冷器热力学模型,分析了蓄冷器中气体微团的热力学变化过程,经计算得出了一周期内总热量和压力波与质量流之间相位的关系,对蓄冷器在制冷系统中的作用提出了新的认识,并通过对脉冲管蓄冷器中交变流动热力学特性的分析,对比一典型的双向进气型脉冲管制冷机的实验测量结果,分析了双向进气环流产生的直流分量对蓄冷器的影响,对脉冲管双向进气产生的直流分量对脉冲管制冷性能的影响提出了新的解释。     

Analysis of flow in the spiral casing using a streamline upwind Petrov Galerkin method

Numerical simulation of complex three‐dimensional flow through the spiral casing has been accomplished using a finite element method. An explicit Eulerian velocity correction scheme has been deployed to solve the Reynolds average Navier–Stokes equations. The simulation has been performed to describe the flow in high Reynolds number (10⁶) regime. For spatial discretization, a streamline upwind Petrov Galerkin technique has been used. The velocity field and the pressure distribution inside the spiral casing corroborate the results available in literature. The flow structure reveals the fact that very strong secondary flow is evolved on the cross‐stream planes. Copyright © 1999 John Wiley & Sons, Ltd.     

Realization of high pressures and temperatures in the gas phase of a bubble liquid flowing through a nozzle

A steady flow of a bubble gas-liquid mixture in a nozzle having a circular cross section has been investigated. The possibility of realization of superhigh temperatures and pressures in the gas phase of the mixture in the region near the smallest cross section of the nozzle has been analyzed. The influence of the initial radius of the flow and the volume content of bubbles, determining the volumetric rate of flow of the liquid supplied to the nozzle, on the pattern of the flow has been considered. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 6, pp. 134–137, November–December, 2007.