Flow of an elastico-viscous fluid past an infinite wall with time-dependent suction

Summary Kelley's solution for the incompressible viscous flow past an infinite wall, with time dependent suction, is extended for an idealized elastico-viscous liquid. The effect of the presence of the elasticity on the velocity field and the skin friction is examined. It is found that the back-flow at the wall is enhanced by the elasticity parameter. The phase angle of the skin friction is also found to decrease with increasing the unsteady part of the suction velocity.     

Flow in a rotating slot channel with injection through one wall and compensating suction through the other

The results of calculating the velocity field and integral characteristics for laminar conditions are presented and analyzed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 54, No. 4, pp. 539–543, April, 1988.     

Flow rate measurement in a pipe flow by vortex shedding

The flow rate measurement of liquid, steam, and gas is one of the most important areas of application for today’s field instrumentation. Vortex meters are used in numerous branches of industry to measure the volumetric flow by exploiting the unsteady vortex flow behind a blunt body. The classical Kármán vortex street behind a cylinder shows a decrease in Strouhal number with decreasing Reynolds number. Considering the flow behind a vortex shedding device in a pipe the Strouhal-Reynolds number dependence shows a different behaviour for turbulent flows: a decrease in Reynolds number leads to an increase in Strouhal number. This phenomenon was found in the experimental investigations as well as in the numerical results and has been confirmed theoretically by a stability analysis.     

制冷系统回气管道中的气锤现象

本文通过对冷库制冷系统回气管道的事故原因分析,并与水锤现象进行对比,说明了制冷系统回气管道中出现气锤现象的原因,并提出了解决气锤现象的方法.     

Oblique flow impinging on a wall with suction or blowing

Summary The oblique flow of a viscous fluid impinging on a flat wall with suction or blowing is studied. It is found that when suction is applied the fluid penetrates the wall while blowing causes the shifting of the stagnation point. It is also found that this shifting depends upon the magnitude of the blowing.     

Boundary layer on a permeable wall with suction of gas

The differential model of turbulence, supplemented with transport equation for turbulent heat flux, is used to perform a numerical investigation of the boundary layer on a permeable wall with suction of gas. It is demonstrated that the protraction of transition from laminar to turbulent mode of flow and the laminarization of the initial turbulent boundary layer occur under conditions of suction of gas. This is evidenced both by the behavior of integral and local characteristics of flow and heat transfer and by the degeneracy of turbulence when the suction of laminar turbulent layer becomes asymptotic. The critical values of the suction parameter are determined.     

Stress intensity factors for long axial surface cracks at the outer wall of a pipe loaded by stress gradients

By means of the finite element method crack opening displacements were calculated for long axial surface cracks at the outer wall of a pipe. The wall thickness to inner radius ratio of the pipe was 1 to 10. Following a procedure introduced be Mattheck et al. weight functions were evaluated by means of the finite element results. Using these weight functions it is possible to calculate stress intensity factors for arbitrary radially varying stress distributions. In this paper stress intensity factors were evaluated for a constant hoop stress loading as well as for stress distributions with a linear and a quadratic dependence on the radius.     

制冷系统回气管道中的气锤现象

本文通过对冷库制冷系统回气管道的事故原因分析,并与水锤现象进行对比,说明了制冷系统回气管道中出现气锤现象的原因,并提出了解决气锤现象的方法     

Stress Intensity Factors of partly circumferential surface cracks at the outer wall of a pipe

By means of the finite element method stress intensity factors were calculated for partly circumferential surface cracks at the outer wall of a pipe. The crack shape considered can be described as curved rectangular shape. The cracks considered have crack depths between 20 and 80 percent of the wall thickness of the pipe and crack lengths (defined by the angle of circumference φ) between φ = 10° and φ = 60°. The pipe is loaded by a constant axial tensile stress σ₀ (equal to 136 Nmm^?2 in the numerial calculations), and the wall thickness to inner radius ratio of the pipe was chosen to 0.1. A wall thickness of 20 mm was used for the numerical calculations.     

Flow regimes of a fluid driven granular suspension

We discuss molecular dynamics simulations of a granular suspension driven in a channel by an embedding fluid. The flow has three different regimes: it is disordered at small packing fractions, ${\phi}$ ; above a transition point, ${\phi_m}$ , flows becomes ordered in layers, but only in a fraction of samples; at higher ${\phi}$ , if ordering is avoided, jamming is also encountered. In the disordered flow regime the velocity profile is power law, consistent with an Ostwald-de Waele constitutive relation. In the ordered regime, flow is concentrated in the bulk in a nearly solid plug having a flat velocity profile, with narrow shear regions at the boundaries. Interestingly, velocity fluctuations are approximately linear in the velocity in all regimes.     

Flow analysis in a channel with a moving wall

Numerical results obtained by solving the complete system of Navier-Stokes equations for a channel with one movable surface are evaluated.     

Heat transfer through a porous plate at cooling gas supply in an asymptotic suction regime

The analytical solution is carried out for the one- and two-dimensional problem of the thermal state of a porous plate surrounded by the flow of high-temperature and homogenous cooling gases in a permeable cooling system. Cooling gas flow in a laminar regime of asymptotic suction is considered, which provides effective heat shielding with minimum dependence on the parameters of the permeable wall. Heat exchange from the high-temperature gas is accepted for both laminar and turbulent boundary layers.     

Laminar flow of a non-Newtonian fluid in channels with wall suction or injection

The one-dimensional approximate equation in the rectangular Cartesian coordinates governing flow of a non-Newtonian fluid confined in two large plates separated by a small distance of h, with the upper plate stationary while the lower plate is uniformly porous and moving in the x-direction with constant velocity, is derived by accounting for the order of magnitude of terms as well as the accompanying approximations to the full-blown three-dimensional equations by using scaling arguments, asymptotic techniques and assuming the cross-flow velocity is much less than the axial velocity. The one-dimensional governing equation for a power-law fluid flow confined between parallel plates, with the upper plate is stationary and the bottom plate subjected to sudden acceleration with a constant velocity in the x-direction and uniformly porous, is solved analytically for a Newtonian fluid case (n = 1) and numerically for various values of power-law index to determine the transient velocity and thus the overall transient velocity distribution. The effects of mass suction/injection at the porous bottom plate on the flow of non-Newtonian fluids are examined for various values of time and power-law index. The results obtained from the present analysis are compared with the data available in the literature.     

Diffraction of acoustic waves by a semi-infinite cylindrical impedance pipe of certain wall thickness

An asymptotic high-frequency solution is presented for the problem of diffraction of acoustic waves emanating from a ring source by a semi-infinite cylindrical pipe of certain wall thickness having different internal, external and end surface impedances. Through the application of the Fourier-transform technique in conjunction with the Mode Matching method, the diffraction problem is described by a modified Wiener–Hopf equation of the second kind and then solved approximately. Various numerical results illustrating the effects of the parameters of the problem on the diffraction phenomenon are presented.     

Deposition of microparticles from a turbulent stream onto a pipe wall

An equation for the flux of particles to the inner wall of a pipe, in good agreement with experimental data, is obtained under certain assumptions about the mechanism of transport of solid microparticles in a turbulent gas or liquid stream. The problem of the variation in the density of microparticles along the length of a pipe is also solved.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 61, No. 1, pp. 56–58, July, 1991.     

Flow transport in a microchannel induced by moving wall contractions: a novel micropumping mechanism

A novel micropumping mechanism based on a theoretical model that describes flow transport in a microchannel induced by moving wall contractions in the low Reynolds number flow regime is presented. The channel is assumed to have a length that is much greater than its width (d = W/L << 1{delta = W/L ll 1}) and the upper wall is subjected to prescribed, non-peristaltic, localized moving contractions. Lubrication theory for incompressible viscous flow at low Reynolds number (R _e ~ δ) is used to model the problem mathematically and to derive expressions for the velocity components, pressure gradient, wall shear stress, and net flow produced by the wall contractions. The effect of contraction parameters such as amplitude and phase lag on the time-averaged net flow over a single cycle of wall motions is studied. The results presented here are supported by passive particle tracking simulations to investigate the possibility of using this system as a pumping mechanism. The present study is motivated by collapse mechanisms observed in entomological physiological systems that use multiple contractions to transport fluid, and the emerging novel microfluidic devices that mimic these systems.     

Qualitative motion of a liquid in an accelerating gas stream

Experimental data are examined on the interaction of liquid drops with the gas stream in a Venturi scrubber, the most promising available equipment.     

Drag on a sphere accelerating rectilinearly in an elastico-viscous fluid

The exact solution for the drag on a sphere moving in an arbitrary manner along a rectilinear path in an otherwise-still elastico-viscous fluid of infinite extent is presented. The Fourier transform technique is used to derive the solution. This technique is based on the fact that drag on an accelerating body can be obtained by integrating the drag on an oscillating body over all possible frequencies. The solution is also expressed in terms of infinite series which is suitable for numerical evaluation of the drag. The solution for the drag on a sphere suddenly brought to uniform motion is presented as an example of this study.     

Erosion rate correlations of a pipe protruded in an abrupt pipe contraction

Erosion is one of the most serious problems in various gas and liquid flow passages such as flow in pipes, pumps, turbines, compressors and many other devices. Sand presence causes loss of pipe wall thickness that can lead to pipe erosion, frequent failures and loss of expensive production time. The importance of this problem is mainly due to many related engineering applications, viz. heat exchangers. In order to reduce the frequency of such pipe erosions, caps in the form of replaceable pipes are protruded in the sudden contraction regions which are exposed to most of the serious erosion rates. In the present work, numerical investigation of the erosion of a pipe protruded in a sudden contraction is presented. The turbulent, steady, 2-D axi-symmetric flow inside an axi-symmetric abrupt contraction pipe with a pipe protrusion embedded in it was solved by steady-state time averaged conservation equations of mass and momentum along with two equation model for turbulence. Particles are tracked using Lagrangian particle tracking. An erosion model was employed to investigate the erosion phenomena for the given geometry. The influence of the different parameters such as the inlet flow velocity (3–10 m/s), the particle diameter (10–400 μm), the protruded pipe geometry (thickness T=1–5 mm and depth H=2–5 mm) and the pipe contraction ratio (Cr=0.25–0.5) on the erosion of pipe protrusion was investigated. Correlations for the influence of inlet flow velocity, depth and thickness of the protruded pipe on the erosion rate are presented.