Numerical Simulation of Confined Swirling Flows of Oldroyd Fluids

2009 ◽  
Author(s):  
Sahand Majidi ◽  
Ashkan Javadzadegan
Keyword(s):  
Numerical Simulation ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Maxwell Model ◽  
Reynolds Numbers ◽  
Weissenberg Number ◽  
Swirling Flows ◽  
Breakdown Phenomenon ◽  
Volume Method ◽  
Upper Convected Maxwell Model

The effect of a fluid’s elasticity has been investigated on the vortex breakdown phenomenon in confined swirling flow. Assuming that the fluid obeys upper-convected Maxwell model as its constitutive equation, the finite volume method together with a collocated mesh was used to calculate the velocity profiles and streamline pattern inside a typical lid-driven swirling flow at different Reynolds and Weissenberg numbers. The flow was to be steady and axisymmetric. Based on the results obtained in this work, it can be concluded that fluid’s elasticity has a strong effect on the secondary flow completely reversing its direction of rotation depending on the Weissenberg number. Even in swirling flows with low ratio of elasticity to inertia, vortex breakdown is postponed to higher Reynolds numbers. Also, the effect of retardation ratio on the flow structure of viscoelastic fluid with the Weissenberg number being constant was surveyed. Based on our results, by decreasing the retardation ratio the flow becomes Newtonian like.

scholarly journals Anisotropic Characteristics of Turbulence Dissipation in Swirling Flow: A Direct Numerical Simulation Study

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Xingtuan Yang ◽  
Nan Gui ◽  
Gongnan Xie ◽  
Jie Yan ◽  
Jiyuan Tu ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Energy Dissipation ◽  
Direct Numerical Simulation ◽  
Large Scale ◽  
Isotropic Turbulence ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Turbulent Energy ◽  
Swirling Flows ◽  
Small Scale

This study investigates the anisotropic characteristics of turbulent energy dissipation rate in a rotating jet flow via direct numerical simulation. The turbulent energy dissipation tensor, including its eigenvalues in the swirling flows with different rotating velocities, is analyzed to investigate the anisotropic characteristics of turbulence and dissipation. In addition, the probability density function of the eigenvalues of turbulence dissipation tensor is presented. The isotropic subrange of PDF always exists in swirling flows relevant to small-scale vortex structure. Thus, with remarkable large-scale vortex breakdown, the isotropic subrange of PDF is reduced in strongly swirling flows, and anisotropic energy dissipation is proven to exist in the core region of the vortex breakdown. More specifically, strong anisotropic turbulence dissipation occurs concentratively in the vortex breakdown region, whereas nearly isotropic turbulence dissipation occurs dispersively in the peripheral region of the strong swirling flows.

Analysis and Numerical Simulation of no Reacting Swirling Flow by Using URANS Approach

2021 ◽  
Vol 57 ◽  
pp. 67-79
Author(s):  
Merouane Habib ◽  
Senouci Mohammed
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Swirling Flow ◽  
Navier Stokes ◽  
Governing Equations ◽  
Simulation Based ◽  
Classical Models ◽  
Recirculation Zones ◽  
Computational Fluid Dynamics Cfd ◽  
Volume Method

In this paper, we investigate the no-reacting swirling flow by using the numerical simulation based to the unsteady Reynolds-averaged Navier-Stokes approach. The numerical simulation was realized by using a computational fluid dynamics CFD code. The governing equations are solved by using the finite volume method with two classical models of turbulence K-epsilon and Shear Stress K-ω. The objective of this paper is therefore to evaluate the performance of the two models in predicting the recirculation zones in a swirled turbulent flow. The current models are validated by comparing the numerical results of the axial, radial and tangential velocities to the experimental data from literature.

The evolution of a perturbed vortex in a pipe to axisymmetric vortex breakdown

1998 ◽  
Vol 366 ◽  
pp. 211-237 ◽  
Author(s):  
Z. RUSAK ◽  
S. WANG ◽  
C. H. WHITING
Keyword(s):  
Vortex Breakdown ◽  
Swirling Flow ◽  
Nonlinear Ordinary Differential Equation ◽  
Swirling Flows ◽  
Axisymmetric Vortex ◽  
Burgers Vortex ◽  
Theoretical Predictions ◽  
Necessary And Sufficient Criteria ◽  
High Reynolds ◽  
Necessary And Sufficient

The evolution of a perturbed vortex in a pipe to axisymmetric vortex breakdown is studied through numerical computations. These unique simulations are guided by a recent rigorous theory on this subject presented by Wang & Rusak (1997a). Using the unsteady and axisymmetric Euler equations, the nonlinear dynamics of both small- and large-amplitude disturbances in a swirling flow are described and the transition to axisymmetric breakdown is demonstrated. The simulations clarify the relation between our linear stability analyses of swirling flows (Wang & Rusak 1996a, b) and the time-asymptotic behaviour of the flow as described by steady-state solutions of the problem presented in Wang & Rusak (1997a). The numerical calculations support the theoretical predictions and shed light on the mechanism leading to the breakdown process in swirling flows. It has also been demonstrated that the fundamental characteristics which lead to vortex instability and breakdown in high-Reynolds-number flows may be calculated from considerations of a single, reduced-order, nonlinear ordinary differential equation, representing a columnar flow problem. Necessary and sufficient criteria for the onset of vortex breakdown in a Burgers vortex are presented.

Significance of the Vortex Breakdown Phenomenon

1965 ◽  
Vol 87 (2) ◽  
pp. 518-522 ◽  
Author(s):  
T. B. Benjamin
Keyword(s):  
Vortex Breakdown ◽  
Swirling Flows ◽  
Longitudinal Vortex ◽  
Vortex Flows ◽  
Breakdown Phenomenon ◽  
Physical Principles

The essential points in the author’s published theory of this phenomenon are summarized, and their implications with regard to longitudinal vortex flows in general are reviewed. The primary aim is to emphasize the physical principles which underlie the theory, and most of the mathematical details are passed over here. It is proposed that these principles serve to rationalize a wide variety of possible behavior in swirling flows.

Effects of Swirling Flows on Pneumatic Transport of Solids in Pipes (Keynote)

2003 ◽  
Author(s):  
Yuji Tomita
Keyword(s):  
Numerical Simulation ◽  
Pressure Drop ◽  
Kinetic Energy ◽  
Total Pressure ◽  
Swirling Flow ◽  
Swirling Flows ◽  
Pneumatic Transport ◽  
Air Velocity ◽  
Low Velocity ◽  
Wall Collision

By applying swirling air flow, particles can be transported with smaller air velocity as compared to the conventional flow without swirl in both horizontal and vertical flows. The total pressure drop along the pipeline is generally larger than that of the flow without swirl, but becomes small and even smaller than that of conventional one when the air velocity decreases. Thus, the swirling flow is effective in low velocity pneumatic transport of suspension mode. By using weak swirl as compared to the previous one, also decreases the particle breakage when the air velocity is low. A numerical simulation shows that the kinetic energy of particles at the wall collision becomes smaller than that in flow without swirl when the breakage is decreased.

scholarly journals Axisymmetric vortex breakdown Part 1. Confined swirling flow

1990 ◽  
Vol 221 ◽  
pp. 533-552 ◽  
Author(s):  
J. M. Lopez
Keyword(s):  
Oscillatory Flow ◽  
Stokes Equations ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Swirling Flows ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Axisymmetric Vortex ◽  
Recirculation Zones ◽  
Visualization Experiments

A comparison between the experimental visualization and numerical simulations of the occurrence of vortex breakdown in laminar swirling flows produced by a rotating endwall is presented. The experimental visualizations of Escudier (1984) were the first to detect the presence of multiple recirculation zones and the numerical model presented here, consisting of a numerical solution of the unsteady axisymmetric Navier-Stokes equations, faithfully reproduces these phenomena and all other observed characteristics of the flow. Further, the numerical calculations elucidate the onset of oscillatory flow, an aspect of the flow that was not clearly resolved by the flow visualization experiments. Part 2 of the paper examines the underlying physics of these vortex flows.

The stability of a trailing line vortex. Part 2. Viscous theory

1974 ◽  
Vol 65 (4) ◽  
pp. 769-779 ◽  
Author(s):  
Martin Lessen ◽  
Frederick Paillet
Keyword(s):  
Critical Reynolds Number ◽  
Swirling Flow ◽  
Reynolds Numbers ◽  
Neutral Curve ◽  
Swirling Flows ◽  
Velocity Defect ◽  
The Stability ◽  
Far Wake ◽  
Disturbance Growth ◽  
Swirl Parameter

In a previous paper, the inviscid stability of a swirling far wake was investigated, and the superposition of a swirling flow on the axisymmetric wake was shown to be initially destabilizing, although all modes investigated eventually become more stable at sufficiently large swirl. The most unstable disturbances were non-axisymmetric modes with negative azimuthal wavenumber n representing helical wave paths opposite in sense to the wake rotation. The disturbance growth rate appeared to increase continuously with |n|, while all modes with |n| > 1 represented disturbances which are completely stable for the non-swirling wake. In the present analysis, both timewise and spacewise growth rates are calculated for the lowest three negative non-axisymmetric modes (n = −1, −2 and −3). Vortex intensity is characterized by a swirl parameter q proportional to the ratio of the maximum swirling velocity to the maximum axial velocity defect. The large wavenumbers associated with the disturbances at large |n| allow the n = −1 mode to have the minimum critical Reynolds number of 16 (q ≃ 0·40). The other two modes investigated have minimum Reynolds numbers on the neutral curve of 31 (n = −2, q = 0·60) and 57 (n = −3, q = 0·80). For each mode, the neutralstability curve is shown to shift rapidly towards infinite Reynolds numbers once the swirl becomes sufficiently large. Some of the most unstable swirling flows are shown to possess spacewise amplification factors almost ten times that for the most unstable wavenumber for the non-swirling wake at moderate Reynolds numbers.

Application of Laser Velocimetry for Characterization of Confined Swirling Flow

1989 ◽  
Vol 111 (1) ◽  
pp. 36-45 ◽  
Author(s):  
A. S. Nejad ◽  
S. P. Vanka ◽  
S. C. Favaloro ◽  
M. Samimy ◽  
C. Langenfeld
Keyword(s):  
Vortex Breakdown ◽  
Swirling Flow ◽  
Swirling Flows ◽  
Interarrival Time ◽  
Mean Flow ◽  
Third Order ◽  
Cold Flow ◽  
Large Samples ◽  
Turbulence Data

A two-component LDV was used in a cold flow dump combustor model to obtain detailed mean and turbulence data for both swirling and nonswirling inlet flows. Large samples were collected to resolve the second and third-order products of turbulent fluctuations with good accuracy. Particle interarrival time weighting was used to remove velocity bias from the data. The swirling flows, with and without vortex breakdown, exhibited significantly different mean flow and turbulent field behavior. A numerical scheme with the k–ε closure model was used to predict the flow fields. Comparison of the numerical and experimental results showed that the k–ε turbulence model is inadequate in representing the complex turbulent structure of confined swirling flows.

Near-critical swirling flow of a viscoelastic fluid in a circular pipe

2017 ◽  
Vol 814 ◽  
pp. 325-360
Author(s):  
Zvi Rusak ◽  
Nguyen Ly ◽  
John A. Tichy ◽  
Shixiao Wang
Keyword(s):  
Reynolds Number ◽  
Viscoelastic Fluid ◽  
Vortex Breakdown ◽  
Shear Thinning ◽  
Weissenberg Number ◽  
Swirling Flows ◽  
Circular Pipe ◽  
Viscoelastic Characteristic ◽  
Mobility Parameter ◽  
Flow Inertia

The interaction between flow inertia and elasticity in high-Reynolds-number, axisymmetric and near-critical swirling flows of an incompressible and viscoelastic fluid in an open finite-length straight circular pipe is studied at the limit of low elasticity. The stresses of the viscoelastic fluid are described by the generalized Giesekus constitutive model. This model helps to focus the analysis on low fluid elastic effects with shear thinning of the viscosity. The application of the Giesekus model to columnar streamwise vortices is first investigated. Then, a nonlinear small-disturbance analysis is developed from the governing equations of motion. It reveals the complicated interactions between flow inertia, swirl and fluid rheology. An effective Reynolds number that links between steady states of swirling flows of a viscoelastic fluid and those of a Newtonian fluid is revealed. The effects of the fluid viscosity, relaxation time, retardation time and mobility parameter on the flow development in the pipe and on the critical swirl for the appearance of vortex breakdown are explored. It is found that in vortex flows with either an axial jet or an axial wake profile, increasing the shear thinning by decreasing the ratio of the viscoelastic characteristic times from one (with fixed values of the Weissenberg number and the mobility parameter) increases the critical swirl ratio for breakdown. Increasing the fluid elasticity by increasing the Weissenberg number from zero (with a fixed ratio of the viscoelastic characteristic times and a fixed value of the mobility parameter) or increasing the fluid mobility parameter from zero (with fixed values of the Weissenberg number and the ratio of viscoelastic times) causes a similar effect. The results may explain the trend of changes in the appearance of breakdown zones as a function of swirl level that were observed in the experiments by Stokes et al. (J. Fluid Mech., vol. 429, 2001, pp. 67–115), where Boger fluids were used. This work extends for the first time the theory of vortex breakdown to include effects of non-Newtonian fluids.

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