Showing papers on "Pipe flow published in 1981"
TL;DR: In this paper, a reasonably uniform mean temperature gradient has been superimposed upon a nearly homogeneous turbulent shear flow in a wind tunnel, and measurements of several moments, one-and two-point correlation functions, spectra, integral scales, microscales, probability densities, and joint probability density of the turbulent velocities, temperature fluctuations, and temperature-velocity products are reported.
Abstract: A reasonably uniform mean temperature gradient has been superimposed upon a nearly homogeneous turbulent shear flow in a wind tunnel. The overheat is small enough to have negligible effect on the turbulence. Away from the wind-tunnel entrance, the transverse statistical homogeneity is good and the temperature fluctuations and their integral scales grow monotonically like the corresponding velocity fluctuations (Harris, Graham & Corrsin 1977). Measurements of several moments, one- and two-point correlation functions, spectra, integral scales, microscales, probability densities, and joint probability densities of the turbulent velocities, temperature fluctuations, and temperature-velocity products are reported. The heat-transport characteristics are much like those of momentum transport, with the turbulent Prandtl number nearly 1. The temperature fluctuation is better correlated with the streamwise than the transverse velocity component, and the cross-component D12 of the turbulent diffusivity tensor has sign opposite to and about twice the magnitude of the diagonal component D22. Some resemblance of directional properties (relative magnitudes of correlation functions, integral scales, microscales) of the temperature with those of the streamwise velocity is also observed. Comparisons of the present data with measurements in the inner part of a heated boundary layer and a fully turbulent pipe flow (x2/d = 0·25) show comparable magnitudes of temperature-velocity correlation coefficients, turbulent Prandtl numbers and ratios of turbulent diffusivities, and show similar shapes of two-point correlation functions.
524 citations
01 Jan 1981
268 citations
TL;DR: A non-orthogonal helical co-ordinate system is introduced and it is found that both curvature and torsion induce non-negligible effects when the Reynolds number is less than about 40.
Abstract: A non-orthogonal helical co-ordinate system is introduced to study the effect of curvature and torsion on the flow in a helical pipe. It is found that both curvature and torsion induce non-negligible effects when the Reynolds number is less than about 40. When the Reynolds number is of order unity, torsion induces a secondary flow consisting of one single recirculating cell while curvature causes an increased flow rate. These effects are quite different from the two recirculating cells and decreased flow rate at high Reynolds numbers.
192 citations
01 Jan 1981
TL;DR: In this article, a theoretical model for core-annular flow of a very viscous oil core and a water annulus through a horizontal pipe was developed, where the core is assumed to be solid and the interface to be a solid/liquid interface.
Abstract: Abstract A theoretical model has been developed for core-annular flow of a very viscous oil core and a water annulus through a horizontal pipe. Special attention was paid to understanding how the buoyancy force on the core, resulting from any density difference between the oil and water, is counterbalanced. This problem was simplified by assuming the oil viscosity to be so high that any flow inside the core may be neglected and hence that there is no variation of the profile of the oil-water interface with time. In the model the core is assumed to be solid and the interface to be a solid/liquid interface. By means of the hydrodynamic lubrication theory it has been shown that the ripples on the interface moving with respect to the pipe wall can generate pressure variations in the annular layer. These result in a force acting perpendicularly on the core, which can counterbalance the buoyancy effect. To check the validity of the model, oil-water core-annular flow experiments have been carried out in a 5.08 cm and an 20.32-cm pipeline. Pressure drops measured have been compared with those calculated with the aid of the model. The agreement is satisfactory.
106 citations
TL;DR: In this article, an analysis of the flow and heat transfer in an interrupted-plate passage, which is an idealization of the offset-fin heat exchanger, is presented, where the plates are considered to be of finite thickness.
102 citations
TL;DR: In this paper, the stability of pipe flow to axisymmetric disturbances is studied by direct numerical simulation of the incompressible Navier-Stokes equations, and no evidence of finite-amplitude equilibria at any of the wavenumber/Reynolds number combinations investigated, with all perturbations decaying on a time scale much shorter than the diffusive (viscous) time scale.
Abstract: The stability of pipe flow to axisymmetric disturbances is studied by direct numerical simulation of the incompressible Navier-Stokes equations. There is no evidence of finite-amplitude equilibria at any of the wavenumber/Reynolds number combinations investigated, with all perturbations decaying on a time scale much shorter than the diffusive (viscous) time scale. In particular, decay is obtained where amplitude-expansion perturbation techniques predict equilibria, indicating that these methods are not valid away from the neutral curve of linear stability theory.
89 citations
TL;DR: In this article, the plane motion of a cantilevered pipe conveying fluid is examined when the flow velocity is in the neighborhood of that generating flutter in contrast to previous studies, the velocity is not prescribed as a constant, but is determined from the laws of motion.
Abstract: The plane motion of a cantilevered pipe conveying fluid is examined when the flow velocity is in the neighborhood of that generating flutter In contrast to previous studies, the flow velocity is not prescribed as a constant, but is determined from the laws of motion A system of two nonlinear partial differential equations which are coupled through the nonlinear terms is thereby obtained The solution is found by the use of the Krylov-Bogoliubov averaging method and the results are discussed indicating the effect of nonlinearities
54 citations
TL;DR: In this paper, a review of existing experimental information on the flow around, and the fluctuating loads on, fixed circular cylinders in uniform streams, including in particular the effects of free-stream turbulence and surface roughness, is presented.
Abstract: A review is presented of existing experimental information on the flow around, and the fluctuating loads on, fixed circular cylinders in uniform streams, including in particular the effects of free-stream turbulence and surface roughness. Dependent parameters examined are the Strouhal number, the root mean square drag, lift, and pressure coefficients, and the correlations and spectra of the fluctuations. The characterization and definition of the various flow regimes (subcritical, critical, supercritical, and transcritical), and the manner of transition between regimes are analyzed, with due regard to the possible three-dimensional nature of the flow and the effect of the inherent flow unsteadiness. Free-stream turbulence effects are examined in the various flow regimes; a limited review of theoretical results is also presented.
47 citations
TL;DR: In this article, a semi-empirical model for adiabatic two-phase annular flow is extended to predict the critical heat flux (CHF) in a vertical pipe, and the model exhibits a sharply declining curve of CHF versus steam quality at low X, and is relatively independent of the heat flux distribution.
41 citations
TL;DR: In this paper, an algorithm is presented for automatically constructing and solving equations describing the behavior of water distribution networks when some pipe characteristics are unknown, based on loop equations and therefore appropriate for implementation on minicomputers.
Abstract: Unknown pipe characteristics may be helpful in the design and operation of water distribution networks. By using unknown pipe characteristics it becomes easier to select appropriate pipes, to choose boosters, and to regulate the flow through pumps using regulating valves. An algorithm is presented for automatically constructing and solving equations describing the behavior of water distribution networks when some pipe characteristics are unknown. It is based on loop equations and is therefore appropriate for implementation on minicomputers. Several applications and experiments are described.
TL;DR: In this paper, the authors introduced four characteristic parameters defined for a pulsating turbulent pipe flow, and the pattern diagrams for pulsating laminar pipe flow were shown, where flow patterns were classified into three types, i.e., quasi-steady, intermediate, and inertia dominant ones with respect to the dimensionless frequency ω' and the limits between these three regions were determined.
Abstract: By introducing four characteristic parameters defined for a pulsating turbulent pipe flow, the pattern diagrams for a pulsating laminar pipe flow are shown. The flow patterns are classified into three types, i. e., quasi-steady, intermediate, and inertia dominant ones with respect to the dimensionless frequency ω' and the limits between these three regions are determined. An alternative analytical representation for wall shear stress τw including acceleration term and its approximation are proposed. Various approximate representations for τw reported previously or proposed here are compared with the analytical one by means of the four characteristic parameters and their applicability is examined.
DOI•
01 Aug 1981TL;DR: In this paper, six different flows involving coherent structures are discussed with varying amounts of detail, including the puff in a pipe, the turbulent spot, the spiral turbulence, the vortex ring, vortex street, and the mixing layer.
Abstract: Six different flows involving coherent structures are discussed with varying amounts of detail. These are the puff in a pipe, the turbulent spot, the spiral turbulence, the vortex ring, the vortex street, and the mixing layer. One central theme is that non-steady similarity arguments and topology are of the essence of coherent structure. Another is that the Reynolds equations, which are sterile when applied to a structureless mean flow, may be quite productive when applied to a single structure. A third theme is the prospect for at least partial control of technically important flows by exploiting the concept of coherent structure.
TL;DR: In this article, an experimental investigation was performed in order to observe the effect of the inclination angle on the transport behavior of a closed two-phase thermosyphon, where a vertical or inclined steel pipe was used; this was electrically heated at the lower part (heating zone) and it was cooled by water at constant temperature along the upper part (cooling zone).
TL;DR: In this paper, the relationship between frictional losses and dimensionless frequency in an incompressible pulsating laminar pipe flow is investigated in terms of three kinds of friction factors.
Abstract: Relations between frictional losses and dimensionless frequency in an incompressible pulsating laminar pipe flow are investigated in terms of three kinds of friction factors. Furthermore, the frictional losses calculated from previously reported various approximate representations for wall shear stress are compared with those calculated from an analytical one in order to examine the validity of approximations. It becomes evident that the behaviours of instantaneous and time average friction factors in the quasi-steady, the intermediate, and the inertia dominant regions are qualitatively similar to those in a pulsating turbulent pipe flow and that the time average friction factor and the root mean square friction factor proposed here can be correlated to time-averaged cross-sectional mean viscous dissipation, while the instantaneous friction factor cannot represent the instantaneous cross-sectional mean viscous dissipation except for the quasi-steady region.
TL;DR: In this paper, a framework for the detailed understanding of two-phase flow multidimensional void distribution mechanisms from the point of view of momentum conservation is provided, and a basis with which experimental data can be compared and interpreted.
Abstract: The purpose of this paper is to provide a framework for the detailed understanding of two-phase flow multidimensional void distribution mechanisms from the point of view of momentum conservation, and thus to provide a basis with which experimental data can be compared and interpreted. An analytical model for the phase distribution mechanisms in fully developed turbulent two-phase flow in channels of arbitrary cross sections is derived. The model has been applied to the special case of cylindrical pipe flow, and compared with existing data. 7 refs.
01 Feb 1981
TL;DR: In this paper, the authors developed a theory for the rate of particulate deposition from turbulent gas streams onto surfaces, where three characteristic times (the particle relaxation time, the turbulent fluctuation time and the particle residence time) controlled the deposition mode.
Abstract: A theory is developed for the rate of particulate deposition from turbulent gas streams onto surfaces. Three characteristic times—the particle relaxation time, the turbulent fluctuation time, and the particle residence time—control the deposition mode. Two phenomena are primarily responsible for transport of the particles across the laminar sublayer and deposition: (1) the momentum imparted to the particle by the fluid turbulence; and (2) the thermospheresis caused by the temperature gradient near the wall. Interaction of the three characteristic times with these two phenomena is analyzed, and the particle deposition rate in turbulent pipe flow is computed. The findings are found to be in close agreement with available experimental data.
TL;DR: In this article, structural features associated with the Reynolds-number dependence of an axisymmetric jet were studied and it was found that transition in the unbounded jet is in the nature of transition in Couette flow and occurs at specific critical values of the Reynolds number rather than in some range over which small disturbances are amplified.
Abstract: Unsteady particle trajectories are used to study structural features associated with the Reynolds-number dependence of an axisymmetric jet It is found that transition in the unbounded jet is in the nature of transition in Couette flow and occurs at specific critical values of the Reynolds number rather than in some range over which small disturbances are amplified In the case of the creeping-flow solution, the particle-path pattern exhibits a structure which is not easily discerned in any of the other variables that govern the flow For sufficiently small Reynolds number, the particle paths converge to a single stable node which lies on the axis of the jet At a Reynolds number of 67806, the pattern bifurcates to a saddle and two stable nodes; at a Reynolds number of 1009089, it bifurcates a second time to form a saddle and two stable foci
TL;DR: In this article, an exact method for obtaining a closure relationship for the transient shear stress in a laminar flow submitted to an arbitrary transient pressure gradient is proposed, and extensive comparisons are given for a step or a harmonic pressure gradient between the approximate solution derived from this method, some results of the literature and exact solutions of the Navier-Stokes equations.
Abstract: The problem of describing an unsteady cylindrical pipe flow with one-dimensional equations is investigated, and an exact method for obtaining a closure relationship is proposed for the transient shear stress in a laminar flow submitted to an arbitrary transient pressure gradient. Extensive comparisons are given for a step or a harmonic pressure gradient between the approximate solution derived from this method, some results of the literature and exact solutions of the Navier–Stokes equations.
TL;DR: In this article, the authors model the flow of a fluid in a pipe by a first order nonlinear hyperbolic system with zero-order nonlinear dissipation, and prove that a unique, global smooth solution exists if the initial data are in an appropriate invariant region and if the first derivatives of the original data are sufficiently small.
Journal Article•
TL;DR: In this paper, the rectilinear pipe flow of a polymeric liquid under a time-dependent pressure drop is considered and perturbation solutions are developed for two integral constitutive equations; both have strain-dependent memory kernels.
Abstract: In this article, the rectilinear pipe flow of a polymeric liquid under a time‐dependent pressure drop is considered. The fluctuating component of the pressure drop is assumed to be of small amplitude and can adequately be represented by a weakly stationary stochastic process. Perturbation solutions are developed for two integral constitutive equations; both have strain‐dependent memory kernels. The first is the recently proposed nonaffine network model and the second is a simplified version of the B‐KBZ constitutive equation. It is shown that both models predict a positive flow rate enhancement. This flow enhancement is a decreasing function of the frequency of the fluctuating pressure drop when the latter is represented by a sinusoidal function of time. Based on the limited data published by Barnes, Townsend, and Walters, it is concluded that both models considered here cannot describe the frequency dependence of the flow enhancement. In this regard, it would appear that an integral model with a strain‐r...
TL;DR: In this paper, the reaction of N2O+X2 Pi with H2 was investigated in flow tubes at room temperature and the reaction ratio of the two components was approximately 5:1.
Abstract: Reactions of HN2O+ have been investigated in flow tubes at room temperature. For the reactions of HN2O+ with both CH4and NO the observations may be described accurately in terms of two components of the reactant ions distinguishable by different reactivities. The ratio of the two components is approximately 5:1. The HN2O+ ions were produced from the reaction of N2O+(X2 Pi ) with H2.
TL;DR: In this paper, the relationship between viscous friction, the energy loss due to the lengthwise rate of change of the kinetic energy coefficient and the total energy loss is investigated and continuous variation of the velocity profile is analyzed by using the concept of a non-Newtonian liquid whose shear sensitivity varies continuously along the pipe.
Abstract: The laminar flow phenomena in the inlet (entrance) region of circular pipe are investigated experimentally. New curves of friction factor versus Reynolds number, for various entry lengths, are obtained and compared with the standard curve for fully developed laminar flow. The relationship between the viscous friction, the energy loss due to the lengthwise rate of change of the kinetic energy coefficient and the total energy loss is investigated. The continuous variation of the velocity profile is analysed by using the concept of a non-Newtonian liquid whose shear sensitivity varies continuously along the pipe.
TL;DR: In this paper, Boussinesq approximated equations for convective heat transfer from a square cavity in a channel with variable inclination were used to investigate the influence of buoyant forces on heat transfer.
TL;DR: In this article, a spatial stability study of the developing flow in a pipe showed that the critical frequency and wavenumber for the Hornbeck profile are larger than those for the Sparrow profile, but the critical Reynolds number is smaller.
Abstract: A spatial stability study of the developing flow in a pipe shows that the critical frequency and wavenumber for the Hornbeck profile are larger than those for the Sparrow profile, but the critical Reynolds number is smaller. Results for the Hornbeck profile are found to be closer to the experimental data.
TL;DR: In this article, extensive spectral measurements of the wall pressure field for flow Mach numbers in the range 0·2-0·5 are presented, and regions where higher order modes are detectable are identified.
TL;DR: The use of jet injections, as contrasted to injections with no momentum, can help to reduce the pipe flow distance required for the mixing of injected and ambient fluids without requiring appurtenances or devices inside the pipe.
Abstract: The use of jet injections, as contrasted to injections with no momentum, can help to reduce the pipe flow distance required for the mixing of injected and ambient fluids without requiring appurtenances or devices inside the pipe. For uniform, turbulent flow, experiments were conducted to determine the optimum injection conditions for a single jet at the pipe wall at 90° to 150° relative to the ambient flow, and for two jets at 90°. Depending on the type of injection and the desired degree of mixing, the required flow distance can be reduced up to 70 percent compared to injection with no momentum. For uniform flow, there are only small benefits from using more than two injection points. However, the two experiments which were conducted with a secondary current in the pipe flow indicated greater benefits from using multiple-point injection.