Characterisation of acoustically linked oscillations in cyclone separators

2015 ◽  
Vol 780 ◽  
pp. 45-59 ◽  
Author(s):  
T. A. Grimble ◽  
A. Agarwal
Keyword(s):  
Strouhal Number ◽  
Vortex Core ◽  
Internal Flow ◽  
Simple Relationship ◽  
Swirl Number ◽  
Precessing Vortex Core ◽  
Scaling Parameters ◽  
Invasive Method ◽  
Dimensional Parameters ◽  
Flow Oscillations

The hydrodynamic oscillations of a cyclone separator – in particular the precessing vortex core (PVC) phenomena – are investigated by measuring their radiated sound spectra. Strong coherence was observed between internal flow oscillations measured via hot wire anemometry and the external acoustic field measured via microphone. This means that the oscillations can be characterised by using acoustics as a proxy. The oscillations cause narrow-band noise, referred to as cyclone hum. System characterisation by dimensional analysis used velocity and length scales of the vortex core region as scaling parameters. The relevant non-dimensional parameters are a Strouhal number for the cyclone hum centre frequency, a Reynolds number, a geometry based swirl number and numerous geometric scales defining the shape of the device. Cyclones with multiple sizes of inlets and outlets were tested at different flow rates using external microphones to detect the cyclone hum. The results produce an excellent collapse of the data, yielding a simple relationship for Strouhal number as a function of swirl number and the outlet diameter ratio. The non-invasive method of examining oscillations that is presented in this paper could be applied to other swirling systems.

scholarly journals The unsteady swirling jet in a model of radial burner

2021 ◽  
Vol 2119 (1) ◽  
pp. 012106
Author(s):  
I V Litvinov ◽  
E U Gorelikov ◽  
S I Shtork
Keyword(s):  
Experimental Study ◽  
Unsteady Flow ◽  
Strouhal Number ◽  
Vortex Core ◽  
Guide Vane ◽  
Swirl Flow ◽  
Acoustic Sensors ◽  
Swirl Number ◽  
Precessing Vortex Core ◽  
Vane Angle

Abstract The experimental study of an isothermal swirl flow with the formation of a precessing vortex core in the radial swirler upon non-confinement and confinement conditions is carried out. Velocity profiles are obtained with varying Re and guide vane angle, changing the swirl number S. Four acoustic sensors and LDA system are used to measure Strouhal number as the function of the integral swirl number in the range from 0.5 <S <0.8. It is shown that the unsteady flow with PVC effect significantly changes upon non-confinement and confinement conditions.

Investigations into the Precessing Vortex Core Phenomenon in Cyclone Dust Separators

1994 ◽  
Vol 208 (2) ◽  
pp. 147-154 ◽  
Author(s):  
P Yazdabadi ◽  
A J Griffiths ◽  
N Syred
Keyword(s):  
Vortex Core ◽  
Reynolds Numbers ◽  
Frequency Parameter ◽  
Experimental Investigations ◽  
Swirl Number ◽  
Significant Drop ◽  
Precessing Vortex Core ◽  
Dust Separator ◽  
The Relationship

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.

Why Non-Uniform Density Suppresses the Precessing Vortex Core

2013 ◽  
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.

Why Nonuniform Density Suppresses the Precessing Vortex Core

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
Kilian Oberleithner ◽  
Steffen Terhaar ◽  
Lothar Rukes ◽  
Christian Oliver Paschereit
Keyword(s):  
Linear Stability ◽  
Vortex Core ◽  
Hydrodynamic Instability ◽  
Density Field ◽  
Sufficient Evidence ◽  
Reacting Flow ◽  
Global Instability ◽  
Global Mode ◽  
Precessing Vortex Core ◽  
Flow Oscillations

Linear stability analysis is applied to a swirl-stabilized combustor flow with the aim to understand how the flame shape and associated density field affects the manifestation of self-excited flow instabilities. In isothermal swirling jets, self-excited flow oscillations typically manifest in a precessing vortex core and synchronized growth of large-scale spiral-shaped vortical structures. Recent theoretical studies relate these dynamics to a hydrodynamic global instability. 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 inhomogeneities created by the flame. This mechanism is revealed by considering two reacting flow configurations: The first configuration represents a perfectly premixed steam-diluted detached flame featuring a strong precessing vortex core. The second represents a perfectly premixed dry 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 in 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 for relating the flame position and the resulting density field to the emergence of a precessing vortex core.

scholarly journals Effect of Nozzle Confinement in the Axial Swirler

2019 ◽  
Vol 196 ◽  
pp. 00032
Author(s):  
Roman Yusupov ◽  
Ivan Litvinov ◽  
Sergey Shtork
Keyword(s):  
Unsteady Flow ◽  
Strouhal Number ◽  
Vortex Core ◽  
Recirculation Zone ◽  
Averaging Method ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Secondary Vortex ◽  
Precessing Vortex Core ◽  
Swirl Parameter

This work is devoted to the study of unsteady flow with the precessing vortex core (PVC) formed at the exit of a compact vane swirler with varying vanes angle and nozzles diameters. Amplitude-frequency characteristics of the PVC were obtained using two microphones. The modified Strouhal number dependence have showed a good generalization of the data for all nozzle diameters. The averaged and phase-averaged distributions of three components of velocity have been measured via the LDA system. The increasing the recirculation zone at increasing nozzle diameter for the swirl parameter Sg=0.53 and Re=1.5·104 was detected. The degeneration of PVC was detected for all studied nozzle diameters D = 30, 40, 50 mm. In case of smallest diameter D = 30 mm the PVC ceases to be periodic due to the absence of a recirculation zone. The three-dimensional structure of the PVC is reconstructed by the phase averaging method and visualized using the Q-criterion. Formation of the shifted recirculation zone, outer secondary vortex (OSV) and inner secondary vortex (ISV) is observed.

LES of Turbulent Swirling Jets: Study of Jet Precession, Recirculation and Vortex Breakdown

2009 ◽  
Author(s):  
Ranga Dinesh ◽  
Karl Jenkins ◽  
Michael Kirkpatrick
Keyword(s):  
Vortex Core ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Vortex Breakdown ◽  
Low Frequency ◽  
Test Case ◽  
Test Cases ◽  
Swirl Number ◽  
Eddy Viscosity Model ◽  
Precessing Vortex Core

Large eddy simulations (LES) of turbulent isothermal swirling flows have been investigated. The Sydney swirl burner configuration has been used for all simulated test cases from a low to a high swirl and Reynolds numbers. Four test cases based on different swirl numbers have been considered and the influence of the swirl number for producing recirculation, vortex breakdown, precession vortex core and the precession frequencies have been investigated. The governing equations for the continuity and momentum are solved on a structured Cartesian grid, and a Smagorinsky eddy viscosity model with the localised dynamic procedure is used as the subgrid scale turbulence model. The results show that the LES successfully predicts both the upstream first recirculation zone generated by the bluff body and the downstream vortex breakdown bubble (VBB) induced by swirl. The plots reveal that the expansion of the upstream recirculation zone is almost similar for each test case. LES results revealed that the increasing swirl number affect to form the VBB in the downstream region, however it promotes the shear layer instability in the recirculation zones. The frequency spectrums indicate the presence of low frequency oscillations and the existence of a central jet precession. Results demonstrated distinct precession frequencies at the considered spatial jet locator and agreed well with the experimental values. The results also highlight the formation of a precessing vortex core (PVC).

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

2021 ◽  
Author(s):  
Arnab Mukherjee ◽  
Nishanth Muthichur ◽  
Chaitali More ◽  
Saarthak Gupta ◽  
Santosh Hemchandra
Keyword(s):  
Vortex Core ◽  
Precessing Vortex Core ◽  
Core Dynamics

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

2018 ◽  
Vol 140 (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.

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

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

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

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.

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