The Role of the Centerbody Wake on the Precessing Vortex Core Dynamics of a Swirl Nozzle

Experimental investigations have been carried out to examine the effect of downstream pipework configurations on the precessing vortex core (PVC) generated within the exhaust region of a cyclone dust separator. Characterization of the PVC using a non-dimensionalized frequency parameter (NDFP) was used to determine the relationship between Reynolds number and geometrical swirl number of the cyclone. The results show that the NDFP tends towards an asymptotic value for Reynolds numbers of about 50 000 and high swirl numbers (> 3.043). This value is reached earlier with lower swirl numbers. It was concluded that any exhaust pipework configuration produced a significant drop in the PVC frequency, and certain configurations either delayed or promoted the development of the PVC.

Download Full-text

Spin wave mediated unidirectional vortex core reversal by two orthogonal monopolar field pulses: The essential role of three-dimensional magnetization dynamics

Journal of Applied Physics ◽

10.1063/1.4948354 ◽

2016 ◽

Vol 119 (17) ◽

pp. 173901 ◽

Cited By ~ 7

Author(s):

Matthias Noske ◽

Hermann Stoll ◽

Manfred Fähnle ◽

Ajay Gangwar ◽

Georg Woltersdorf ◽

...

Keyword(s):

Spin Wave ◽

Vortex Core ◽

Essential Role ◽

Three Dimensional ◽

Magnetization Dynamics

Download Full-text

Impact of Precessing Vortex Core Dynamics on Shear Layer Response in a Swirling Jet

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4038324 ◽

2018 ◽

Vol 140 (6) ◽

Cited By ~ 6

Author(s):

Mark Frederick ◽

Kiran Manoharan ◽

Joshua Dudash ◽

Brian Brubaker ◽

Santosh Hemchandra ◽

...

Keyword(s):

Stability Analysis ◽

Shear Layer ◽

Linear Stability ◽

Linear Stability Analysis ◽

Vortex Core ◽

Combustion Instability ◽

Forced Response ◽

Longitudinal Acoustic ◽

Precessing Vortex Core ◽

Acoustic Forcing

Combustion instability, the coupling between flame heat release rate oscillations and combustor acoustics, is a significant issue in the operation of gas turbine combustors. This coupling is often driven by oscillations in the flow field. Shear layer roll-up, in particular, has been shown to drive longitudinal combustion instability in a number of systems, including both laboratory and industrial combustors. One method for suppressing combustion instability would be to suppress the receptivity of the shear layer to acoustic oscillations, severing the coupling mechanism between the acoustics and the flame. Previous work suggested that the existence of a precessing vortex core (PVC) may suppress the receptivity of the shear layer, and the goal of this study is to first, confirm that this suppression is occurring, and second, understand the mechanism by which the PVC suppresses the shear layer receptivity. In this paper, we couple experiment with linear stability analysis to determine whether a PVC can suppress shear layer receptivity to longitudinal acoustic modes in a nonreacting swirling flow at a range of swirl numbers. The shear layer response to the longitudinal acoustic forcing manifests as an m = 0 mode since the acoustic field is axisymmetric. The PVC has been shown both in experiment and linear stability analysis to have m = 1 and m = −1 modal content. By comparing the relative magnitude of the m = 0 and m = −1,1 modes, we quantify the impact that the PVC has on the shear layer response. The mechanism for shear layer response is determined using companion forced response analysis, where the shear layer disturbance growth rates mirror the experimental results. Differences in shear layer thickness and azimuthal velocity profiles drive the suppression of the shear layer receptivity to acoustic forcing.

Download Full-text

Why Non-Uniform Density Suppresses the Precessing Vortex Core

Volume 1B: Combustion, Fuels and Emissions ◽

10.1115/gt2013-95509 ◽

2013 ◽

Cited By ~ 5

Author(s):

Kilian Oberleithner ◽

Steffen Terhaar ◽

Lothar Rukes ◽

Christian Oliver Paschereit

Keyword(s):

Natural Gas ◽

Vortex Core ◽

Hydrodynamic Instability ◽

Density Field ◽

Density Stratification ◽

Reacting Flow ◽

Global Instability ◽

Global Mode ◽

Precessing Vortex Core ◽

Flow Oscillations

Isothermal swirling jets undergoing vortex breakdown are known to be susceptible to self-excited flow oscillations. They manifest in a precessing vortex core and synchronized growth of large-scale vortical structures. Recent theoretical studies associate these dynamics with the onset of a global hydrodynamic instability mode. These global modes also emerge in reacting flows, thereby crucially affecting the mixing characteristics and the flame dynamics. It is, however, observed that these self-excited flow oscillations are often suppressed in the reacting flow, while they are clearly present at isothermal conditions. This study provides strong evidence that the suppression of the precessing vortex core is caused by density stratification created by the flame. This mechanism is revealed by considering two reacting flow configurations: The first configuration represents a detached steam-diluted natural gas swirl-stabilized flame featuring a strong precessing vortex core. The second represents a natural gas swirl-stabilized flame anchoring near the combustor inlet, which does not exhibit self-excited oscillations. Experiments are conducted in a generic combustor test rig and the flow dynamics are captured using PIV and LDA. The corresponding density fields are approximated from the seeding density using a quantitative light sheet technique. The experimental results are compared to the global instability properties derived from hydrodynamic linear stability theory. Excellent agreement between the theoretically derived global mode frequency and measured precession frequency provide sufficient evidence to conclude that the self-excited oscillations are, indeed, driven by a global hydrodynamic instability. The effect of the density field on the global instability is studied explicitly by performing the analysis with and without density stratification. It turns out that the significant change on instability is caused by the radial density gradients in the inner recirculation zone and not by the change of the mean velocity field. The present work provides a theoretical framework to analyze the global hydrodynamic instability of realistic combustion configurations. It allows relating the flame position and the resulting density field to the emergence of a precessing vortex core.

Download Full-text

Numerical simulation of precessing vortex core dumping by localized nonstationary heat source

10.1063/1.4965381 ◽

2016 ◽

Author(s):

Denis Porfiriev ◽

Anastasiya Gorbunova ◽

Igor Zavershinsky ◽

Semen Sugak ◽

Nonna Molevich

Keyword(s):

Numerical Simulation ◽

Heat Source ◽

Vortex Core ◽

Nonstationary Heat ◽

Precessing Vortex Core

Download Full-text

Direct Determination of Large Spin-Torque Nonadiabaticity in Vortex Core Dynamics

Physical Review Letters ◽

10.1103/physrevlett.105.187203 ◽

2010 ◽

Vol 105 (18) ◽

Cited By ~ 53

Author(s):

L. Heyne ◽

J. Rhensius ◽

D. Ilgaz ◽

A. Bisig ◽

U. Rüdiger ◽

...

Keyword(s):

Vortex Core ◽

Direct Determination ◽

Spin Torque ◽

Core Dynamics ◽

Large Spin

Download Full-text

Stability and Sensitivity Analysis of Hydrodynamic Instabilities in Industrial Swirled Injection Systems

Volume 4A: Combustion, Fuels and Emissions ◽

10.1115/gt2017-63649 ◽

2017 ◽

Author(s):

Thomas L. Kaiser ◽

Thierry Poinsot ◽

Kilian Oberleithner

Keyword(s):

Stability Analysis ◽

Linear Stability ◽

Linear Stability Analysis ◽

Vortex Core ◽

Large Eddy Simulations ◽

Mode Shapes ◽

Mean Flow ◽

Precessing Vortex Core ◽

Large Eddy ◽

Good Agreement

The hydrodynamic instability in an industrial, two-staged, counter-rotative, swirled injector of highly complex geometry is under investigation. Large eddy simulations show that the complicated and strongly nonparallel flow field in the injector is superimposed by a strong precessing vortex core. Mean flow fields of large eddy simulations, validated by experimental particle image velocimetry measurements are used as input for both local and global linear stability analysis. It is shown that the origin of the instability is located at the exit plane of the primary injector. Mode shapes of both global and local linear stability analysis are compared to a dynamic mode decomposition based on large eddy simulation snapshots, showing good agreement. The estimated frequencies for the instability are in good agreement with both the experiment and the simulation. Furthermore, the adjoint mode shapes retrieved by the global approach are used to find the best location for periodic forcing in order to control the precessing vortex core.

Download Full-text