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.

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.

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.

scholarly journals The impedance boundary condition for acoustics in swirling ducted flow

2018 ◽  
Vol 849 ◽  
pp. 645-675 ◽  
Author(s):  
Vianney Masson ◽  
James R. Mathews ◽  
Stéphane Moreau ◽  
Hélène Posson ◽  
Edward J. Brambley
Keyword(s):  
Boundary Condition ◽  
Surface Waves ◽  
Swirling Flow ◽  
Swirling Flows ◽  
Impedance Boundary Condition ◽  
Mean Flow ◽  
Thin Boundary Layer ◽  
Impedance Boundary ◽  
Unstable Surface ◽  
The Stability

The acoustics of a straight annular lined duct containing a swirling mean flow is considered. The classical Ingard–Myers impedance boundary condition is shown not to be correct for swirling flow. By considering behaviour within the thin boundary layers at the duct walls, the correct impedance boundary condition for an infinitely thin boundary layer with swirl is derived, which reduces to the Ingard–Myers condition when the swirl is set to zero. The correct boundary condition contains a spring-like term due to centrifugal acceleration at the walls, and consequently has a different sign at the inner (hub) and outer (tip) walls. Examples are given for mean flows relevant to the interstage region of aeroengines. Surface waves in swirling flows are also considered, and are shown to obey a more complicated dispersion relation than for non-swirling flows. The stability of the surface waves is also investigated, and as in the non-swirling case, one unstable surface wave per wall is found.

Flashback in a Swirl Burner With Cylindrical Premixing Zone

2001 ◽  
Author(s):  
Jassin Fritz ◽  
Martin Kröner ◽  
Thomas Sattelmayer
Keyword(s):  
Flame Propagation ◽  
Gas Turbines ◽  
High Speed ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Laser Doppler Anemometry ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Measurement Techniques ◽  
Mean Flow

Flame flashback from the combustion chamber into the mixing zone is one of the inherent problems of lean premixed combustion and essentially determines the reliability of low NOx burners. Generally, flashback can be initiated by one of the following four phenomena: flashback due to the conditions in the boundary layer, flashback due to turbulent flame propagation in the core flow, flashback induced by combustion instabilities and flashback caused by combustion induced vortex breakdown. In this study, flashback in a swirling tubular flow was investigated. In order to draw maximum benefit from the tests with respect to the application in gas turbines, the radial distribution of the axial and circumferential momentum in the tube was selected such that the typical character of a flow in mixing zones of premix burners without centerbody was obtained. A single burner test rig has been designed to provoke flashback with the preheating temperature, the equivalence ratio and the mean flow rate being the influencing parameters. The flame position within the mixing section is detected by a special optical flame sensor array, which allows the control of the experiment and furthermore the triggering of the measurement techniques. The burning velocity of the fuel has been varied by using natural gas or hydrogen. The characteristics of the flashback, the unsteady swirling flow during the flame propagation, the flame dynamics and the reaction zones have been investigated by applying High Speed Video recordings, the Laser Doppler Anemometry and the Laser Induced Fluorescence. The presented results show that a combustion induced vortex breakdown is the dominating mechansim of the observed flashback. This mechanism is very sensitive to the momentum distribution in the vortex core. By adding axial momentum around the mixing tube axis, the circumferential velocity gradient is reduced and flashback can be prevented.

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 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.

Flashback in a Swirl Burner With Cylindrical Premixing Zone

2004 ◽  
Vol 126 (2) ◽  
pp. 276-283 ◽  
Author(s):  
J. Fritz ◽  
M. Kro¨ner ◽  
T. Sattelmayer
Keyword(s):  
Flame Propagation ◽  
Gas Turbines ◽  
High Speed ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Laser Doppler Anemometry ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Measurement Techniques ◽  
Mean Flow

Flame flashback from the combustion chamber into the mixing zone is one of the inherent problems of lean premixed combustion and essentially determines the reliability of low NOx burners. Generally, flashback can be initiated by one of the following four phenomena: flashback due to the conditions in the boundary layer, flashback due to turbulent flame propagation in the core flow, flashback induced by combustion instabilities and flashback caused by combustion induced vortex breakdown. In this study, flashback in a swirling tubular flow was investigated. In order to draw maximum benefit from the tests with respect to the application in gas turbines, the radial distribution of the axial and circumferential momentum in the tube was selected such that the typical character of a flow in mixing zones of premix burners without centerbody was obtained. A single burner test rig has been designed to provoke flashback with the preheating temperature, the equivalence ratio and the mean flow rate being the influencing parameters. The flame position within the mixing section is detected by a special optical flame sensor array, which allows the control of the experiment and furthermore the triggering of the measurement techniques. The burning velocity of the fuel has been varied by using natural gas or hydrogen. The characteristics of the flashback, the unsteady swirling flow during the flame propagation, the flame dynamics and the reaction zones have been investigated by applying high-speed video recordings, the laser Doppler anemometry and the laser induced fluorescence. The presented results show that a combustion induced vortex breakdown is the dominating mechanism of the observed flashback. This mechanism is very sensitive to the momentum distribution in the vortex core. By adding axial momentum around the mixing tube axis, the circumferential velocity gradient is reduced and flashback can be prevented.

scholarly journals Dual vortex breakdown in a two-fluid whirlpool

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sergey G. Skripkin ◽  
Bulat R. Sharifullin ◽  
Igor V. Naumov ◽  
Vladimir N. Shtern
Keyword(s):  
Vortex Breakdown ◽  
Swirling Flow ◽  
Immiscible Fluids ◽  
Swirling Flows ◽  
Disk Drives ◽  
Circulation Cell ◽  
Lower Fluid ◽  
Culture Growth ◽  
Rotation Strength ◽  
Two Fluid

AbstractLooking for an optimal flow shape for culture growth in vortex bioreactors, an intriguing and impressive structure has been observed that mimics the strong swirling flows in the atmosphere (tornado) and ocean (waterspout). To better understand the flow nature and topology, this experimental study explores the development of vortex breakdown (VB) in a lab-scale swirling flow of two immiscible fluids filling a vertical cylindrical container. The rotating bottom disk drives the circulation of both fluids while the sidewall is stationary. The container can be either sealed with the still top disk (SC) or open (OC). As the rotation strength (Re) increases, a new circulation cell occurs in each fluid—the dual VB. In case SC, VB first emerges in the lower fluid at Re = 475 and then in the upper fluid at Re = 746. In case OC, VB first emerges in the upper fluid at Re = 524 and then in the lower fluid at Re = 538. The flow remains steady and axisymmetric with the interface and the free surface being just slightly deformed in the studied range of Re. Such two-VB swirling flows can provide efficient mixing in aerial or two-fluid bioreactors.

Planar Investigation of Outlet Boundary Conditions Effect on Isothermal Flow Fields of a Swirl-Stabilized Burner

2009 ◽  
Author(s):  
Ahmed Emara ◽  
Arnaud Lacarelle ◽  
Christian Oliver Paschereit
Keyword(s):  
Coherent Structures ◽  
Swirling Flow ◽  
Streamwise Velocity ◽  
Flow Conditions ◽  
Mean Flow ◽  
Cold Flow ◽  
Contraction Ratio ◽  
The Mean ◽  
Pod Analysis ◽  
Proper Orthogonal

The swirling flow velocity profiles can be strongly influenced by the outlet conditions of the combustion chamber especially at subcritical flow conditions. The effect of such changes on the mean flow or coherent structures is still unclear. It is investigated in the present work in an industrial swirl inducing burner in cold flow conditions with help of PIV. Proper orthogonal decomposition (POD) as well as acoustic measurements were used to characterize the coherent structures shed from the burner mouth. The combustor length (670, and 2020mm) and the outlet area contraction ratio (1, 0.56, 0.27, and 0.09) are varied. Major changes in the flow field are achieved when using a short combustor and the smallest contraction ratio. For this case, a central jet with streamwise velocity is added to the typical central recirculation zone. The POD analysis of the contraction ratios 1 and 0.09 for the long combustor shows that the first helical mode as well as Kelvin Helmholtz vortices are present with minor changes for both cases. At a contraction ratio of 0.09, some new structures at the jet location and near the combustor wall appear.

Numerical Studies on Trapped-Vortex Concepts for Stable Combustion

1998 ◽  
Vol 120 (1) ◽  
pp. 60-68 ◽  
Author(s):  
V. R. Katta ◽  
W. M. Roquemore
Keyword(s):  
Drag Coefficient ◽  
Reacting Flow ◽  
Flow Conditions ◽  
Third Order ◽  
Cold Flow ◽  
Flow Simulations ◽  
Numerical Studies ◽  
Dynamic Flows ◽  
Experimental Findings ◽  
Trapped Vortex

Spatially locked vortices in the cavities of a combustor aid in stabilizing the flames. On the other hand, these stationary vortices also restrict the entrainment of the main air into the cavity. For obtaining good performance characteristics in a trapped-vortex combustor, a sufficient amount of fuel and air must be injected directly into the cavity. This paper describes a numerical investigation performed to understand better the entrainment and residence-time characteristics of cavity flows for different cavity and spindle sizes. A third-order-accurate time-dependent Computational Fluid Dynamics with Chemistry (CFDC) code was used for simulating the dynamic flows associated with forebody-spindle-disk geometry. It was found from the nonreacting flow simulations that the drag coefficient decreases with cavity length and that an optimum size exists for achieving a minimum value. These observations support the earlier experimental findings of Little and Whipkey (1979). At the optimum disk location, the vortices inside the cavity and behind the disk are spatially locked. It was also found that for cavity sizes slightly larger than the optimum, even though the vortices are spatially locked, the drag coefficient increases significantly. Entrainment of the main flow was observed to be greater into the smaller-than-optimum cavities. The reacting-flow calculations indicate that the dynamic vortices developed inside the cavity with the injection of fuel and air do not shed, even though the cavity size was determined based on cold-flow conditions.

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