Flow In Circular Pipe Research Articles

A driving mechanism of a turbulent puff in pipe flow

A turbulent puff is numerically realized in a circular pipe flow driven by a constant uniform external force. The periodic boundary condition is imposed in the axial direction with a period of 16π pipe radius. The Reynolds number based on the pipe radius, the centerline velocity of the Hagen–Poiseuille flow corresponding to the external force, is 3000. Starting with the Hagen–Poiseuille flow superposed by a disturbance of finite amplitude, an equilibrium puff of about 11π pipe radius in length emerges and advects with nearly the mean flow velocity. Turbulence in the puff generates a number of low-speed streaks accompanied by streamwise vortices along the pipe wall. These low-speed streaks move upstream relative to the puff, across the trailing edge and create strong thin vortex layers, arched above the streaks, together with the laminar flow coming from upstream. The vortex layers, whose thickness is typically a few times smaller than the width, are unstable to roll up, through the Kelvin–Helmholtz instability, and induce velocity fluctuations that propagate downstream faster than the puff itself and enhance the turbulent activity in it. This self-sustenance cycle of an equilibrium puff is numerically verified.

Experimental Investigation of the Jets in Crossflow: Nonswirling Flow Case

The mixing of eight isothermal jets issuing in a fully developed circular pipe flow is investigated by means of laser Doppler anemometry, particle image velocimetry, and planar laser induced fluorescence techniques. Two values of the momentum ratio are considered. Unsteady and steady flow patterns are analyzed. Characteristic frequencies are deduced from spectral analysis. Velocity and scalar concentration fields are compared. The mean centerline concentration decay is characterized. The analysis of the flow instabilities is focused on the wake-type structures downstream of the jets and the shear layer structures appearing between the jet and the main flow. The results on the wake-type structures are consistent with previous observations done on a single jet. In particular, the influence of the velocity ratio on the signal-to-noise ratio is confirmed. The Strouhal number associated with the shear layer structure depends on the velocity ratio and on the Reynolds number. The comparison between the velocity and concentration fields confirms the difference in the jet trajectories deduced from these two fields. The detailed analysis of the concentration field gives useful information on the influence of the confinement on the jets' behavior.

Meshless local boundary integral equation (LBIE) method for the unsteady magnetohydrodynamic (MHD) flow in rectangular and circular pipes

The meshless local boundary integral equation (LBIE) method is given to obtain the numerical solution of the coupled equations in velocity and magnetic field for unsteady magnetohydrodynamic (MHD) flow through a pipe of rectangular and circular sections with non-conducting walls. Computations have been carried out for different Hartmann numbers and at various time levels. The method is based on the local boundary integral equation with moving least squares (MLS) approximation. For the MLS, nodal points spread over the analyzed domain, are utilized to approximate the interior and boundary variables. A time stepping method is employed to deal with the time derivative. Finally, numerical results are presented to show the behaviour of velocity and induced magnetic field.

Hydraulic analysis of averaged parameters of turbulent flows in circular pipes and plane channels

Variation in the position of three characteristic (conditional) layers of a flow is investigated.

Nanofluids forced convection heat transfer inside circular tubes

Two-dimensional turbulent convective heat transfer behaviour of alumina (Al2O3) nanoparticle dispersion in water flow in a horizontal circular pipe at constant wall temperature is investigated numerically. The computational procedure is based on the finite-volume technique. Three stream velocities corresponding to 5,000 < Re < 4 × 106 and five different concentrations of nanoparticle (0%, 1%, 2%, 4% and 6%) are studied. The full range of flow at the entrance length and the fully developed are considered. The shear stress are observed to increase at any x station along the pipe as the concentration of nanoparticle increase and it attains its higher value at the beginning of the pipe at the entrance region and then drops to an asymptotic value at the fully developed region. However, the case is reversed for Nusselt numbers along the pipe wall where they decrease as the concentration increase at each specific velocity value and in general as the velocity increases both Nusselt number and the shear stress increase. Different envelopes are obtained for Nusselt numbers and the shear stress in terms of Reynolds number. Finally, Reynolds number is observed to decrease as the concentration increase at fixed inlet velocity.

Estimation of Unknown Boundary Heat Flux in Laminar Circular Pipe Flow Using Functional Optimization Approach: Effects of Reynolds Number

An inverse forced convection problem was studied in this paper. The unknown space-dependent heat flux at the outer boundary of a circular pipe was identified from the temperature measurements within the flow using the algorithm based on an improved conjugate gradient method, which is a combination of the modified inverse algorithm proposed by Ozisik et al. (Huang and Ozisik, 1992, “Inverse Problem of Determining Unknown Wall Heat Flux in Laminar Flow Through a Parallel Plate Duct,” Numer. Heat Transfer, Part A 21, pp. 2615–2618) and the general inverse algorithm based on the conjugate gradient method. The effects of the convection intensity, the number of thermocouples, the location of the thermocouples, and the measurement error on the performance of the modified inverse algorithm method and the improved inverse algorithm were studied thoroughly through three examples. It is shown that the improved inverse algorithm can greatly improve the solution accuracy in the entire computation domain. The accuracy and stability of both the modified inverse algorithm method and the improved inverse algorithm are strongly influenced by the Reynolds number and the shape of the unknown heat flux. Those functions, which contain more high-frequency components of Fourier series, are more sensitive to the increase in the Reynolds number.

Structure of a Turbulent Puff in Pipe Flow

The flow in a circular pipe of radius a driven by a constant and uniform axial force is investigated over a range of Reynolds numbers, including the critical value for laminar–turbulent transition. The Navier–Stokes equation for an incompressible viscous fluid is solved numerically by a spectral method as the initial value problem with the no-slip boundary condition on the pipe wall and periodic boundary conditions with period 16π a in the axial direction. The initial condition is given by the Hagen–Poiseuille flow (corresponding to the external force) superimposed with perturbations of finite amplitude. The long-term behaviour of the flow is qualitatively different depending on the Reynolds number Re = U a /ν, where U is the centerline velocity of the above Hagen–Poiseuille flow and ν is the kinematic viscosity of the fluid. For intermediate Reynolds numbers (3300≤ Re ≤4000) we find a locally turbulent region, called a “puff”, which is advected downstream with velocity close to the mean axial velocity. T...

Instantaneous Liquid Flow Rate Measurement Utilizing the Dynamics of Laminar Pipe Flow

This paper deals with the utilization of the dynamic characteristics of laminar flow in circular pipes for the indirect measurement of flow rates. A discrete-time state space realization of the transmission line dynamics is computed via inverse Laplace transform and an identification and model reduction method based on the singular value decomposition. This dynamic system is used for the computation of the flow rate at one end of a pipe section. Special attention is paid to the identification of the speed of sound and the dimensionless dissipation number of the pipe section, since exact knowledge of these parameters is crucial for the reliability of the measurement results. First, experimental validation results are given in a limited range of operating frequencies between 100 Hz and 2000 Hz. Flow rate variations within ±1.2 l/min have been measured with an uncertainty of ±0.07 l/min at the 95% confidence level. The test fluid was mineral oil.

Lifetime statistics in transitional pipe flow

Several experimental and numerical studies have shown that turbulent motions in circular pipe flow near transitional Reynolds numbers may not persist forever, but may decay. We study the properties of these decaying states within direct numerical simulations for Reynolds numbers up to 2200 and in pipes with lengths equal to 5, 9, and 15 times the diameter. We show that the choice of the ensemble of initial conditions affects the short time parts of lifetime distributions, but does not change the characteristic decay rate for long times. Comparing lifetimes for pipes of different length we notice a linear increase in the characteristic lifetime with length, which reproduces the experimental results when extrapolated to 30 diameters, the length of an equilibrium turbulent puff at these Reynolds numbers.

On the rate of spatial predictability in near-wall turbulence

Spatial evolution of small perturbations introduced into an inlet cross-section of fully developed turbulent flow in a long straight circular pipe is investigated via direct numerical simulation (DNS). The turbulent inflow field is extracted from an auxiliary streamwise-periodic simulation running in parallel with the main spatial simulation. It is shown that mean perturbation amplitude ϵ increases exponentially with distance downstream. The growth rate is found to be constant when normalized by viscous length, ϵ ~ exp(0.0021x+) over the considered Reynolds-number range 140 ≤ Reτ ≤ 320. The universal character of perturbation growth is confirmed by channel-flow simulations.

Experimental study of the flow in helical circular pipes: Torsion effect on the flow velocity and turbulence

An objective of the present paper is to experimentally clarify the torsion effect on the flow in helical circular pipes. We have made six helical circular pipes having different pitches and common non-dimensional curvature δ of about 0.1. The torsion parameter β0, which is defined by β0 = τ/(2δ)1/2 with non-dimensional torsion τ, are taken to be 0.02, 0.45, 0.69, 1.01, 1.38 and 1.89 covering from small to very large pitch. The velocity distributions and the turbulence of the flow are measured using an X-type hot-wire anemometer in the range of the Reynolds number from 200 to 20000. The results obtained are summarized as follows: The mean secondary flow pattern in a cross section of the pipe changes from an ordinary twin-vortex type as is seen in a curved pipe without torsion (toroidal pipe) to a single vortex type after one of the twin-vortex gradually disappears as β0 increases. The circulation direction of the single vortex is the same as the direction of torsion of the pipe. The mean velocity distribution of the axial flow is similar to that of the toroidal pipe at small β0, but changes its shape as β0 increases, and attains the shape similar to that in a straight circular pipe when β0 = 1.89. It is also found that the critical Reynolds number, at which the flow shows a marginal behavior to turbulence, decreases as β0 increases for small β0, and then increases after taking a minimum at β0 ≈ 1.4 as β0 increases. The minimum of the critical Reynolds number experimentally obtained is about 400 at β0 ≈ 1.4.

Modeling particle segregation in dilute particle/fluid circular pipe flows

Simulation of the particle segregation phenomenon observed in pipe flows of solid particle/liquid dispersions is carried out using a two fluid model of dilute fully developed flow. Both analytical and numerical results are reported and a new shear lift model is proposed which is capable of predicting a variety of observed phenomena.

Simplification of formulas for compression wave and oscillating flow in circular pipe

We had already obtained the analytical solutions for the compression wave and steady-state oscillating flow in a pipe with a circular cross section [Sato Y, Kanki H. Formulas for compression wave and oscillating flow in circular pipe. To be published in Appl Acoust [accepted 11 Sept. 2006]]. This work contains three key-components. The first key is to simplify the formulas using the unique mathematic technique without losing the accuracy. Simplifying the formulas is the one of the most important factors for formulas used in engineering use. The results will enable us to greatly reduce the work and computation costs. The second is to verify the flow distribution calculated by our formulas. The third is to study the possibility of application of our method to the analysis in turbulent flow region. Kawata et al. have represented the validity of one-dimensional quasi-analysis in turbulent flow region, using the method of D’Souza et al. and the shear viscosity. Therefore, in this paper the validity of the analysis in a turbulence region was verified by proving theoretically that the methods of D’Souza et al. and ours are intrinsically equivalent. The proof of equivalence was accomplished using the formulas simplified in this paper.

Numerical tests of a new molecule-dependent momentum transport equation

It is shown that a new incompressible fluid equation is obtained by inclusion of a new dimensionless coupling parameter in the momentum transport equation derived in [L. Jirkovsky, L. Bo-ot, Momentum transport equation for the fluids using projection–perturbation formalism and onset of turbulence, Physica A 352 (2005) 241–251] from the Boltzmann kinetic equation where the Boltzmann collision integral includes inelastic interactions of quantum origin among the particles of the fluid. Numerical results from the equation for the plane and circular Poiseuille flows are consistent with the observations. The numerical tests also manifest a difference in the onset of turbulence between the flat plates and the circular pipe flow systems. Although all obtained velocity profiles are flattened at the center–a feature of turbulence–the results demonstrate greater stability of the velocity profiles in the circular pipe flow.

Modeling of Unsteady Laminar Flow Based on Steady Solution in Jetting Dispensing Process

This paper proposes a new approach to model unsteady laminar flows of dispenser systems in the semiconductor packaging industry. The approach is based on the exact steady solution. After an overview of dispensing technology and historical modeling of the unsteady flows, a new modeling approach of the unsteady laminar flow in a circular pipe and annular duct is developed. From the proposed model, the modeling results of unsteady flow in an arbitrary circular pipe and annular duct are obtained and compared with the spectral solution. In addition, a comparative work between the proposed analytical dynamic model and the finite-element model is undertaken in order to demonstrate the effectiveness of the proposed modeling methodology.

Micro-PIV Measurements in Micro-Tubes and Proboscis of Mosquito

Effects of the relative size of a particle to the diameter of a micro-tube on velocity profiles obtained by the micro-PIV measurement of the flow through the micro-tube were investigated to achieve the accuracy of measurements of the flow in a proboscis of a mosquito. The velocity profiles obtained for different diameter-ratios of a fluorescent particle and fused silica micro-tube were compared with the exact solution of the velocity profile of flow through a circular pipe at a low Reynolds number. A suitable diameter-ratio was found to be less than 0.04. The velocity profile of flow through the proboscis of a mosquito measured by using the suitable micro-PIV method satisfying the above condition was found to be different from the exact solution of the circular-pipe flow near the center of the proboscis. The velocity profile in the proboscis was similar to that of a rectangular cross section which was verified by a SEM observation.

Modelling of stratified gas–liquid two-phase flow in horizontal circular pipes

This paper reports numerical and experimental investigation of stratified gas–liquid two-phase flow in horizontal circular pipes. The Reynolds averaged Navier–Stokes equations (RANS) with the k– ω turbulence model for a fully developed stratified gas–liquid two-phase flow are solved by using the finite element method. A smooth interface surface is assumed without considering the effects of the interfacial waves. The continuity of the shear stress across the interface is enforced with the continuity of the velocity being automatically satisfied by the variational formulation. For each given interface position and longitudinal pressure gradient, an inner iteration loop runs to solve the non-linear equations. The Newton–Raphson scheme is used to solve the transcendental equations by an outer iteration to determine the interface position and pressure gradient for a given pair of volumetric flow rates. Favorable comparison of the numerical results with available experimental results indicates that the k– ω model can be applied for the numerical simulation of stratified gas–liquid two-phase flow.

Heat Transfer Performance for High Prandtl and High Temperature Molten Salt Flow in Sphere-Packed Pipes

Heat transfer performance for high Prandtl number and high temperature molten salt flow in a circular pipe and in sphere-packed pipes are evaluated with modified Tohoku-NIFS Thermofluid Loop (TNT loop) using high-temperature molten salt HTS (KNO3 : NaNO2 : NaNO3 = 53 : 40 : 7), as a stimulant of Flibe (LiF : BeF2 = 66 : 34). The modified TNT loop has much longer entrance region to develop a thermal boundary layer, which enable us to obtain more precise heat transfer data.In the modified TNT loop experiments, the heat transfer characteristics in a circular pipe flow have good agreements with the representative correlations. It is obvious that the analogy for heat and momentum transfer is also valid for high-temperature and high-Prandtl-number molten salt flow. It is also confirmed that the heat transfer performance of sphere-packed pipes increases up to about 4 times higher than that of circular pipe, in case of relatively low flow rate. This can be effective in the Flibe blanket system from the viewpoints of moderating MHD effect and electrolysis.

Spatial periodicity of spatially evolving turbulent flow caused by inflow boundary condition

Space-time evolution of a flow in a semi-infinite circular pipe {x⩾0,y2+z2⩽R2} is investigated via direct numerical simulations. The unsteady turbulent inflow velocity u∣x=0 is extracted from a streamwise-periodic auxiliary simulation. It is shown that at t≫0 spatially evolving flow does not depend on initial state u∣t=0. It takes the form of spatially periodic flow of the auxiliary simulation with superimposed spatially growing perturbation. The amplitude of the perturbation increases exponentially with distance from the inlet. The growth rate is estimated for the considered Reynolds number. The obtained results suggest that the memory of the inflow boundary condition in spatial simulations is evident for a significant distance from the inlet. In the considered case an almost periodic flow is established (with less than 1% relative deviation from the periodicity) over a distance as large as 70 pipe radii.

비이온계 계면활성제 첨가수에 대한 관내 유동저항 감소 및 열전달 촉진에 관한 연구

This paper has dealt with the effect of non ionized surfactant and water mixture on drag reduction and heat transfer enhancement in a circular pipe flow with experimentally. The test section was consisted of stainless steel pipe with inside diameter of 16mm. The wire coil was used to increase heat transfer in a pipe and the non ionized surfactant(Oleyl Dihydroxyethyl Amine Oxide, ODEAO) was used to reduce the drag force of water mixture with surfactant. The main parameters of this experiment were diameter and pitch of wire coil and the ratio of test section length and horizontal wire coil length. In this experiment, the acquired results were 1) Drag reduction effect existed in this ODEAO-water mixture, 2) Friction factor and heat transfer were increased with insertion the heat transfer enhancement coil, 3) With increasing of pitch ratio, heat transfer was decreased, and 4) Heat transfer was decreased by the decreasing of inserting coil diameter.