Development of Accelerating Pipe Flow Starting From Rest

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Ivar Annus ◽  
Tiit Koppel ◽  
Laur Sarv ◽  
Leo Ainola
Keyword(s):  
Pipe Flow ◽  
Large Scale ◽  
Transformation Method ◽  
Transition To Turbulence ◽  
Navier Stokes ◽  
Axial Velocity Component ◽  
Flow Equations ◽  
Continuity Equations ◽  
Start Up ◽  
Experimental Findings

A uniformly accelerated laminar flow in a pipe, initially at rest, is analyzed. One-dimensional unsteady flow equations for start-up flow were derived from the Navier–Stokes and continuity equations. The dynamical boundary layer in a pipe is described theoretically with the Laplace transformation method for small values of time. A mathematical model describing the development of the velocity profile for accelerating flow starting from rest up to the point of transition to turbulence is given. The theoretical results are compared with experimental findings gained in a large-scale pipeline. Particle image velocimetry (PIV) technique is used to deduce the development of accelerating pipe flow starting from rest. The measured values of the axial velocity component are found to be in a good agreement with the analytical values.

Identification of Transition to Turbulence in a Highly Accelerated Start-Up Pipe Flow

2005 ◽  
Vol 128 (4) ◽  
pp. 680-686 ◽  
Author(s):  
T. Koppel ◽  
L. Ainola
Keyword(s):  
Pipe Flow ◽  
Laplace Transformation ◽  
Transformation Method ◽  
Transition To Turbulence ◽  
Unsteady Boundary Layer ◽  
Physical Explanation ◽  
Pipe Flows ◽  
Flow Parameters ◽  
Start Up ◽  
Laplace Transformation Method

The transition from a laminar to a turbulent flow in highly accelerated start-up pipe flows is described. In these flows, turbulence springs up simultaneously over the entire length of the pipe near the wall. The unsteady boundary layer in the pipe was analyzed theoretically with the Laplace transformation method and the asymptotic method for small values of time. From the experimental results available, relationships between the flow parameters and the transition time were derived. These relationships are characterized by the analytical forms. A physical explanation for the regularities in the turbulence spring-up time is proposed.

Stability of Hagen-Poiseuille flow with superimposed rigid rotation

1976 ◽  
Vol 73 (1) ◽  
pp. 153-164 ◽  
Author(s):  
P.-A. Mackrodt
Keyword(s):  
Poiseuille Flow ◽  
Pipe Flow ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Neutral Curve ◽  
Rigid Rotation ◽  
Transition To Turbulence ◽  
Navier Stokes ◽  
Navier Stokes Equations

The linear stability of Hagen-Poiseuille flow (Poiseuille pipe flow) with superimposed rigid rotation against small three-dimensional disturbances is examined at finite and infinite axial Reynolds numbers. The neutral curve, which is obtained by numerical solution of the system of perturbation equations (derived from the Navier-Stokes equations), has been confirmed for finite axial Reynolds numbers by a few simple experiments. The results suggest that, at high axial Reynolds numbers, the amount of rotation required for destabilization could be small enough to have escaped notice in experiments on the transition to turbulence in (nominally) non-rotating pipe flow.

Disturbance energy growth in core–annular flow

2014 ◽  
Vol 747 ◽  
pp. 44-72 ◽  
Author(s):  
A. Orazzo ◽  
G. Coppola ◽  
L. de Luca
Keyword(s):  
Pipe Flow ◽  
Annular Flow ◽  
Three Dimensional ◽  
Point Of View ◽  
Transition To Turbulence ◽  
Navier Stokes ◽  
Water Mixture ◽  
Horizontal Pipe ◽  
Transient Phenomena ◽  
Modal Theory

AbstractThe linear stability of the horizontal pipe flow of an equal density oil–water mixture, arranged as acore–annular flow(CAF), is here reconsidered from the point of view of non-modal analysis in order to assess the effects of non-normality of the linearized Navier–Stokes operator on the transient evolution of small disturbances. The aim of this investigation is to give insight into physical situations in which poor agreement occurs between the predictions of linear modal theory and classical experiments. The results exhibit high transient amplifications of the energy of three-dimensional perturbations and, in analogy with single-fluid pipe flow, the largest amplifications arise for non-axisymmetric disturbances of vanishing axial wavenumber. Energy analysis shows that the mechanisms leading to these transient phenomena mostly occur in the annulus, occupied by the less viscous fluid. Consequently, higher values of energy amplifications are obtained by increasing the gap between the core and the pipe wall and the annular Reynolds number. It is argued that these linear transient mechanisms of disturbance amplification play a key role in explaining the transition to turbulence of CAF.

Oscillating Pipe Flow: High-Resolution Simulation of Nonlinear Mechanisms

2006 ◽  
Author(s):  
Arash Ghasemi
Keyword(s):  
Pipe Flow ◽  
Stokes Equations ◽  
Stationary Flow ◽  
Current Approach ◽  
Laminar Flows ◽  
Transition To Turbulence ◽  
Navier Stokes ◽  
Frequency Change ◽  
Starting Point ◽  
Corner Points

A new perspective suitable for understanding the details of nonlinear pumping (formation of traveling shocks) inside a pressurized cavity is constructed in this paper. Full compressible axisymmetric three-dimensional Navier-Stokes equations are used as the starting point to cover all complexities of the problem that exceedingly increase for particular ranges of Mach, Reynolds and Prandtl numbers. Then a very high-order numerical method is introduced to preserve the user-defined order of accuracy for practical simulations. For removal of spurious waves, higher-order compact filters are derived. All equations are marched in time using the classical Runge-Kutta algorithm which is appropriate for problems involving fine-scale temporal fluctuations. As the most important part of simulation, Navier-Stokes Characteristic Boundary Conditions are used for accurate calculation of wave reflection specially at singular points, i.e., corner points and points across the axis of symmetry. A simultaneous characteristic-decomposition is devised in this paper which completely resolves stability problems arising from problem-dependent treatment of corner points. Numerical experiments are performed for high-Reynolds laminar flows inside the shock region to determine the effect of frequency change on both shock formation (stationary flow) and transient solution. The current approach which favorably compares to the previous experimental data, may be used as a robust tool for understanding the less-understood problem of shock/Stokes-Layer interaction and its consequences on transition to turbulence in Oscillating Pipe Flow.

scholarly journals Efficient Simulations of Large Scale Convective Heat Transfer Problems

2021 ◽  
Vol 22 (4) ◽  
Author(s):  
Damian Goik ◽  
Krzysztof Banaś ◽  
Jan Bielański ◽  
Kazimierz Chłoń
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Large Scale ◽  
Stokes Equations ◽  
Parallel Implementation ◽  
Navier Stokes ◽  
Flow Equations ◽  
Transfer Problems

We describe an approach for efficient solution of large scale convective heat transfer problems, formulated as coupled unsteady heat conduction and incompressible fluid flow equations. The original problem is discretized in time using classical implicit methods, while stabilized finite elements are used for space discretization. The algorithm employed for the discretization of the fluid flow problem uses Picard's iterations to solve the arising nonlinear equations. Both problems, heat transfer and Navier-Stokes quations, give rise to large sparse systems of linear equations. The systems are solved using iterative GMRES solver with suitable preconditioning. For the incompressible flow equations we employ a special preconditioner based on algebraic multigrid (AMG) technique. The paper presents algorithmic and implementation details of the solution procedure, which is suitably tuned, especially for ill conditioned systems arising from discretizations of incompressible Navier-Stokes equations. We describe parallel implementation of the solver using MPI and elements of PETSC library. The scalability of the solver is favourably compared with other methods such as direct solvers and standard GMRES method with ILU preconditioning.  

Pipe flow measurements over a wide range of Reynolds numbers using liquid helium and various gases

2002 ◽  
Vol 461 ◽  
pp. 51-60 ◽  
Author(s):  
CHRIS J. SWANSON ◽  
BRIAN JULIAN ◽  
GARY G. IHAS ◽  
RUSSELL J. DONNELLY
Keyword(s):  
Liquid Helium ◽  
Pipe Flow ◽  
Scaling Laws ◽  
Reynolds Numbers ◽  
Transition To Turbulence ◽  
Navier Stokes ◽  
Flow Measurements ◽  
Wide Range ◽  
Flow Apparatus ◽  
Stokes Fluid

We demonstrate that an unusually small pipe flow apparatus using both liquid helium and room temperature gases can span an enormous range of Reynolds numbers. This paper describes the construction and operation of the apparatus in some detail. A wide range of Reynolds numbers is an advantage in any experiment seeking to establish scaling laws. This experiment also adds to evidence already in hand that the normal phase of liquid helium is a Navier–Stokes fluid. Finally, we explore recent questions concerning the influence of molecular motions on the transition to turbulence (Muriel 1998) and are unable to observe any influence.

RANS-Based VLES of Thermal and Magnetic Convection at Extreme Conditions

2003 ◽  
Author(s):  
K. Hanjalic´ ◽  
S. Kenjeresˇ
Keyword(s):  
Large Scale ◽  
Cell Structure ◽  
Convective Cell ◽  
Navier Stokes ◽  
Stochastic Motion ◽  
Wall Boundary Layer ◽  
Order Of Magnitude ◽  
Magnetic Convection ◽  
Experimental Findings ◽  
Very High

For thermal and magnetic convection at very high Rayleigh and Hartman numbers, which are inaccessible to the conventional large eddy simulation (LES), we propose a time-dependent Reynolds-average-Navier-Stokes (T-RANS) approach in which the large-scale deterministic motion is fully resolved by time and space solution, whereas the unresolved stochastic motion is modelled by a “subscale” model for which an one-point RANS closure is used. The resolved and modelled contribution to the turbulence moments are of the same order of magnitude and in near-wall regions the modelled heat transport becomes dominant, emphasizing the role of the subscale model. This VLES approach, with an algebraic stress/flux subscale model, verified earlier in comparison with direct numerical simulation (DNS) and experiments in classic Rayleigh-Be´nrad convection, is now expanded to simulate Rayleigh-Be´nard (R-B) convection at very high Ra numbers — at present up to O(1016) — and to magnetic convection in strong uniform magnetic fields. The simulations reproduce the convective cell structure and its reorganization caused by an increase in Ra number and effects of the magnetic field. The T-RANS simulations of classic R-B indicate expected thinning of both the thermal and hydraulic wall boundary layer with an increase in the Ra number and an increase in the exponent of the Nu ∝ Ran correlation in accord with recent experimental findings and Kraichnan asymptotic theory.

scholarly journals Turbulence Model Sensitivity and Scour Gap Effect of Unsteady Flow around Pipe: A CFD Study

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Abbod Ali ◽  
R. K. Sharma ◽  
P. Ganesan ◽  
Shatirah Akib
Keyword(s):  
Transient Flow ◽  
Flow Behavior ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Turbulence Models ◽  
Horizontal Velocity ◽  
Gap Effect ◽  
Navier Stokes ◽  
Flow Equations ◽  
Continuity Equations

A numerical investigation of incompressible and transient flow around circular pipe has been carried out at different five gap phases. Flow equations such as Navier-Stokes and continuity equations have been solved using finite volume method. Unsteady horizontal velocity and kinetic energy square root profiles are plotted using different turbulence models and their sensitivity is checked against published experimental results. Flow parameters such as horizontal velocity under pipe, pressure coefficient, wall shear stress, drag coefficient, and lift coefficient are studied and presented graphically to investigate the flow behavior around an immovable pipe and scoured bed.

Research and Develop on Static Frequency Converter of Pumped Storage Power Plant

2012 ◽  
Vol 608-609 ◽  
pp. 1120-1126 ◽  
Author(s):  
De Shun Wang ◽  
Bo Yang ◽  
Lian Tao Ji
Keyword(s):  
Power Plant ◽  
Control Strategy ◽  
Large Scale ◽  
Frequency Converter ◽  
Position Estimation ◽  
Position Sensor ◽  
Storage Unit ◽  
Rotor Position ◽  
Start Up ◽  
Pumped Storage

A static frequency converter start-up control strategy for pumped-storage power unit is presented. And rotor position detecting without position sensor is realized according to voltage and magnetism equations of ideal synchronous motor mathematics model. The mechanism and implementation method of initial rotor position determination and rotor position estimation under low frequency without position sensor are expounded and validated by simulations. Based on the mentioned control strategy, first set of a static frequency converter start-up device in China for large-scale pumped-storage unit is developed, which is applied to start-up control test in the 90 MW generator/motor of Panjiakou Pumped-storage Power Plant. Test results show that rotor position detecting, pulse commutation, natural commutation, and unit synchronous procedure control of static start-up are all proved. The outcomes have been applied in running equipment, which proves the feasibility of mentioned method.

scholarly journals Effect of an oscillating time-dependent pressure gradient on Dean flow: transient solution

2020 ◽  
Vol 9 (1) ◽  
Author(s):  
Basant K. Jha ◽  
Dauda Gambo
Keyword(s):  
Pressure Gradient ◽  
Initial Conditions ◽  
Fluid Velocity ◽  
Outer Cylinder ◽  
Time Dependent ◽  
Navier Stokes ◽  
Dean Flow ◽  
Continuity Equations ◽  
Riemann Sum ◽  
Flow Formation

Abstract Background Navier-Stokes and continuity equations are utilized to simulate fully developed laminar Dean flow with an oscillating time-dependent pressure gradient. These equations are solved analytically with the appropriate boundary and initial conditions in terms of Laplace domain and inverted to time domain using a numerical inversion technique known as Riemann-Sum Approximation (RSA). The flow is assumed to be triggered by the applied circumferential pressure gradient (azimuthal pressure gradient) and the oscillating time-dependent pressure gradient. The influence of the various flow parameters on the flow formation are depicted graphically. Comparisons with previously established result has been made as a limit case when the frequency of the oscillation is taken as 0 (ω = 0). Results It was revealed that maintaining the frequency of oscillation, the velocity and skin frictions can be made increasing functions of time. An increasing frequency of the oscillating time-dependent pressure gradient and relatively a small amount of time is desirable for a decreasing velocity and skin frictions. The fluid vorticity decreases with further distance towards the outer cylinder as time passes. Conclusion Findings confirm that increasing the frequency of oscillation weakens the fluid velocity and the drag on both walls of the cylinders.

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