scholarly journals Excitation of the precessing vortex core by active flow control to suppress thermoacoustic instabilities in swirl flames

2019 ◽  
Vol 11 ◽  
pp. 175682771985623 ◽  
Author(s):  
Finn Lückoff ◽  
Kilian Oberleithner
Keyword(s):  
Vortex Core ◽  
Oscillation Amplitude ◽  
Premixed Flames ◽  
Current Control ◽  
Minor Effect ◽  
Continuous Increase ◽  
Combustion Dynamics ◽  
Thermoacoustic Instabilities ◽  
Precessing Vortex Core ◽  
The Impact

In this study, we apply periodic flow excitation of the precessing vortex core at the centerbody of a swirl-stabilized combustor to investigate the impact of the precessing vortex core on flame shape, flame dynamics, and especially thermoacoustic instabilities. The current control scheme is based on results from linear stability theory that determine the precessing vortex core as a global hydrodynamic instability with its maximum receptivity to open-loop actuation located near the center of the combustor inlet. The control concept is first validated at isothermal conditions. This is of utmost importance for the proceeding studies that focus on the exclusive impact of the precessing vortex core on the combustion dynamics. Subsequently, the control is applied to reacting conditions considering lean premixed turbulent swirl flames. Considering thermoacoustically stable flames first, it is shown that the actuation locks onto the precessing vortex core when it is naturally present in the flame, which allows the precessing vortex core frequency to be controlled. Moreover, the control allows the precessing vortex core to be excited in conditions where it is naturally suppressed by the flame, which yields a very effective possibility to control the precessing vortex core amplitude. The control is then applied to thermoacoustically unstable conditions. Considering perfectly premixed flames first, it is shown that the precessing vortex core actuation has only a minor effect on the thermoacoustic oscillation amplitude. However, we observe a continuous increase of the thermoacoustic frequency with increasing precessing vortex core amplitude due to an upstream displacement of the mean flame and resulting reduction of the convective time delay. Considering partially premixed flames, the precessing vortex core actuation shows a dramatic reduction of the thermoacoustic oscillation amplitude. In consideration of the perfectly premixed cases, we suspect that this is caused by the precessing vortex core-enhanced mixing of equivalence ratio fluctuations at the flame root and due to a reduction of time delays due to mean flame displacement.

The Effects of Exit Boundary Condition on Precessing Vortex Core Dynamics

2019 ◽  
Author(s):  
Danielle Mason ◽  
Sean Clees ◽  
Mark Frederick ◽  
Jacqueline O’Connor
Keyword(s):  
Boundary Condition ◽  
Vortex Core ◽  
Gas Turbines ◽  
Vortex Breakdown ◽  
Base Flow ◽  
Eigenvalue Decomposition ◽  
Precessing Vortex Core ◽  
Swirling Jet ◽  
Exit Boundary ◽  
The Impact

Abstract Many industrial combustion systems, especially power generation gas turbines, use fuel-lean combustion to reduce NOx emissions. However, these systems are highly susceptible to combustion instability, the coupling between combustor acoustics and heat release rate oscillations of the flame. It has been shown in previous work by the authors that a precessing vortex core (PVC) can suppress shear layer receptivity to external perturbations, reducing the potential for thermoacoustic coupling. The goal of this study is to understand the effect of combustor exit boundary condition on the flow structure of a swirling jet to increase fundamental understanding of how combustor design impacts PVC dynamics. The swirling jet is generated with a radial-entry, variable-angle swirler, and a quartz cylinder is fixed on the dump plane for confinement. Combustor exit constriction plates of different diameters are used to determine the impact of exit boundary condition on the flow field. Particle image velocimetry (PIV) is used to capture the velocity field inside the combustor. Spectral proper orthogonal decomposition, a frequency-resolved eigenvalue decomposition that can identify energetic structures in the flow, is implemented to identify the PVC at each condition in both energy and frequency space. We find that exit boundary diameter affects both the structure of the flow and the dynamics of the PVC. Higher levels of constriction (smaller diameters) force the downstream stagnation point of the vortex breakdown bubble upstream, resulting in greater divergence of the swirling jet. Further, as the exit diameter decreases, the PVC becomes less energetic and less spatially defined. Despite these changes in the base flow and PVC coherence, the PVC frequency is not altered by the exit boundary constriction. These trends will help inform our understanding of the impact of boundary conditions on both static and dynamic flame stability.

Characterization of Different Actuator Designs for the Control of the Precessing Vortex Core in a Swirl-Stabilized Combustor

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Finn Lückoff ◽  
Moritz Sieber ◽  
Christian Oliver Paschereit ◽  
Kilian Oberleithner
Keyword(s):  
Feedback Control ◽  
Vortex Core ◽  
Pressure Sensors ◽  
Pollutant Emissions ◽  
Mean Flow ◽  
Thermoacoustic Instabilities ◽  
Precessing Vortex Core ◽  
System A ◽  
Excellent Control ◽  
Lock In

The precessing vortex core (PVC) represents a helical-shaped coherent flow structure typically occurring in both reacting and nonreacting swirling flows. Until now, the fundamental impact of the PVC on flame dynamics, thermoacoustic instabilities, and pollutant emissions is still unclear. In order to identify and investigate these mechanisms, the PVC needs to be controlled effectively with a feedback control system. A previous study successfully applied feedback control in a generic swirling jet setup. The next step is to transfer this approach into a swirl-stabilized combustor, which poses big challenges on the actuator and sensor design and placement. In this paper, different actuator designs are investigated with the goal of controlling the PVC dynamics. The actuation strategy aims to force the flow near the origin of the instability—the so-called wavemaker. To monitor the PVC dynamics, arrays of pressure sensors are flush-mounted at the combustor inlet and the combustion chamber walls. The best sensor placement is evaluated with respect to the prediction of the PVC dynamics. Particle image velocimetry (PIV) is used to evaluate the passive impact of the actuator shape on the mean flow field. The performance of each actuator design is evaluated from lock-in experiments showing excellent control authority for two out of seven actuators. All measurements are conducted at isothermal conditions in a prototype of a swirl-stabilized combustor.

Phase-Opposition Control of the Precessing Vortex Core in Turbulent Swirl Flames for Investigation of Mixing and Flame Stability

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Finn Lückoff ◽  
Moritz Sieber ◽  
Christian Oliver Paschereit ◽  
Kilian Oberleithner
Keyword(s):  
Control System ◽  
Flow Control ◽  
Turbulent Mixing ◽  
Vortex Core ◽  
Small Scale ◽  
Precessing Vortex Core ◽  
Flame Dynamics ◽  
Flow Control System ◽  
The Impact ◽  
Opposition Control

Abstract The precessing vortex core (PVC) is a helically shaped coherent flow structure that occurs in reacting and nonreacting swirling flows undergoing vortex breakdown. In swirl-stabilized combustors, the PVC affects important phenomena, such as turbulent mixing and thermoacoustic oscillations. In this work, a closed-loop flow control system is developed, which allows for phase-opposition control of the PVC, to achieve appropriate conditions to systematically investigate the influence of the PVC on turbulent flames. The control consists of a zero-net-mass-flux actuator placed in the mixing section of the combustor, where the PVC is most receptive to periodic forcing. The flow control system is characterized from pressure measurements and particle image velocimetry (PIV) and the impact on flame dynamics is extracted from OH*-chemiluminescence measurements. The data reveal that the PVC amplitude is considerably suppressed by the phase-opposition control without changing the overall characteristics of flow and flame, which is crucial to study the exclusive effect of the PVC on combustion processes. Moreover, the control allows the PVC amplitude to be adjusted gradually to investigate the PVC impact on turbulent mixing and flame dynamics. It is revealed that the PVC-induced flow fluctuations mainly affect the large-scale mixing, while the small scale mixing remains unchanged. This is because the suppression of the PVC allows other modes to become more dominant and the overall turbulent kinetic energy (TKE) budget remains unchanged. The destabilization of other modes, such as the axisymmetric mode, may have some implications on thermoacoustic instability.

The Research of the Swirling Flow of the Power Fluid during its Passing through the Hydrodynamic Cavitator

2020 ◽  
pp. 53-71
Author(s):  
Ya. Ya. Yakymechko ◽  
Ya. М. Femiak
Keyword(s):  
Flow Rate ◽  
Vibration Frequency ◽  
Vortex Core ◽  
Swirling Flow ◽  
Theoretical Research ◽  
Theoretical Dependence ◽  
Flow Swirl ◽  
Precessing Vortex Core ◽  
Speed Fluctuation ◽  
The Impact

The article presents the theoretical research of the use of swirling flows with reverse jets and with developed precessing vortex core in cavitators and other devices. While describing the motion of the vortex core in the free swirling jet of the fluid it is necessary to take into account that according to the experimental data the vortex core can swirl along the length of the jet and moves around the jet axis in the zone between the area of reverse flows and the boundary outer layer. In this case, it is the vortex core which is under the influence of the basic swirling flow. Herewith, it is necessary to take into account that due to commensurate sizes of the vortex core and the jet, the impact on the core will be different owing to non-uniform distribution of speeds in the jet itself. On the basis of the known formulas, the authors have deduced the improved theoretical dependence of the degree of flow swirl on the flow rate, the vortex core vibration frequency and structural parameters under the conditions of the consistency of swirling flow itself. The theoretical dependence shows that the degree of flow swirl is directly proportional to the precessing vortex core vibration frequency and inversely proportional to the square of mass flow rate. Thus, ensuring the consistency of the swirling flow with varying flow-rate requires the corresponding change of the swirl degree or the influence on the frequency of vibrations of the precessing vortex core. On the basis of the deduced theoretical dependences, the authors have developed and implemented in the computer programs the following calculations: the dependence of the coefficient of the flow swirl on the vortex core vibration frequency; the simulation of the precession of the vortex core in the swirling flow; the research of speed fluctuation in the swirling flow; speed fluctuation during the interaction of swirling jets.  

Mean field coupling mechanisms explaining the impact of the precessing vortex core on the flame transfer function

2021 ◽  
Vol 223 ◽  
pp. 254-266
Author(s):  
Finn Lückoff ◽  
Thomas Ludwig Kaiser ◽  
Christian Oliver Paschereit ◽  
Kilian Oberleithner
Keyword(s):  
Transfer Function ◽  
Vortex Core ◽  
Mean Field ◽  
Field Coupling ◽  
Precessing Vortex Core ◽  
The Impact ◽  
Coupling Mechanisms

scholarly journals Experimental investigations of ion current in liquid-fuelled gas turbine combustors

2017 ◽  
Vol 9 (3) ◽  
pp. 172-185 ◽  
Author(s):  
J Christopher Wollgarten ◽  
Nikolaos Zarzalis ◽  
Fabio Turrini ◽  
Antonio Peschiulli
Keyword(s):  
Feedback Control ◽  
Vortex Core ◽  
Ion Current ◽  
Injection System ◽  
Experimental Investigations ◽  
Control Loop ◽  
Combustion Dynamics ◽  
Lean Blowout ◽  
Precessing Vortex Core ◽  
Interaction Mode

This work covers investigations of the static and dynamic behaviour of a confined, co-swirled and liquid-fuelled airblast injection system. The focus lies on the application of ion current sensors for the qualitative measurement of the heat release rate or for flame monitoring purposes in complex technical combustion processes. The ion current sensor is to operate in a feedback control loop in order to react on combustion dynamics in real time. The first part of the work analyses experimental data, which were obtained with different techniques, e.g. dynamic pressure, chemiluminescence, fine-wire thermocouples and ion current. The results show that the thermo-acoustic instability and the precessing vortex core generate an interaction mode. The frequency of this interaction mode is the difference of the other two modes. This has not yet been observed for partially premixed and liquid-fuelled injection systems before and also was not detected by the chemiluminescence of the flame. The ion current measurement technique is able to detect the helical mode of the precessing vortex core as well as the interaction frequency, leading to the conclusion that the chemical reactions are influenced by this helical structure. Contour maps of the frequencies reveal this influence in the outer shear layer. The second part of the study focused on the ion current probe as a method to predict static combustion instabilities, such as lean blowout. According to the results, the ion current is a fast responding method to detect lean blowout, provided that the detector is mounted at a suitable position. Measurements at different positions in the flame were compared with phase-locked chemiluminescence measurements. Precursors in the ion current signal for lean-blowout prediction were found using a statistical approach, which is based on ion peak distance. The precursor events allow for the use of this approach with a feedback control loop in future applications.

Characterization of Different Actuator Designs for the Control of the Precessing Vortex Core in a Swirl-Stabilized Combustor

2017 ◽  
Author(s):  
Finn Lückoff ◽  
Moritz Sieber ◽  
Christian Oliver Paschereit ◽  
Kilian Oberleithner
Keyword(s):  
Feedback Control ◽  
Vortex Core ◽  
Pressure Sensors ◽  
Pollutant Emissions ◽  
Mean Flow ◽  
Thermoacoustic Instabilities ◽  
Precessing Vortex Core ◽  
System A ◽  
Excellent Control ◽  
Lock In

The precessing vortex core (PVC) represents a helical-shaped coherent flow structure typically occurring in both reacting and non-reacting swirling flows. Until now the fundamental impact of the PVC on flame dynamics, thermoacoustic instabilities and pollutant emissions is still unclear. In order to identify and investigate these mechanisms, the PVC needs to be controlled effectively with a feedback control system. A previous study successfully applied feedback control in a generic swirling jet setup. The next step is to transfer this approach into a swirl-stabilized combustor, which poses big challenges on the actuator and sensor design and placement. In this paper, different actuator designs are investigated with the goal of controlling the PVC dynamics. The actuation strategy aims to force the flow near the origin of the instability — the so-called wavemaker. To monitor the PVC dynamics, arrays of pressure sensors are flush-mounted at the combustor inlet and the combustion chamber walls. The best sensor placement is evaluated with respect to the prediction of the PVC dynamics. Particle image velocimetry is used to evaluate the passive impact of the actuator shape on the mean flow field. The performance of each actautor design is evaluated from lock-in experiments showing excellent control authority for two out of seven actuators. All measurements are conducted at isothermal conditions in a prototype of a swirl-stabilized combustor.

Impact of Hydrogen Addition On the Thermoacoustic Instability and Precessing Vortex Core Dynamics in a CH4/H2/Air Technically Premixed Combustor

2021 ◽  
Author(s):  
Anindya Datta ◽  
Saarthak Gupta ◽  
Ianko Chterev ◽  
Isaac Boxx ◽  
Santosh Hemchandra
Keyword(s):  
Strain Rate ◽  
Vortex Core ◽  
Thermal Power ◽  
Driving Mechanism ◽  
Thermoacoustic Instability ◽  
Operating Modes ◽  
Precessing Vortex Core ◽  
Lift Off ◽  
The Impact ◽  
Thermoacoustic Oscillations

Abstract We study the impact of H2 enrichment on the unsteady flow dynamics and thermoacoustic instability in PRECCINSTA swirl combustor. The experiments were performed at atmospheric conditions with H2/CH4 fuel mixtures at a global equivalence ratio of 0.65 and a constant thermal power of 20 kW. We analyze data with three fuel compositions: 0%, 20% and 50% H2 in two operating modes, premixed (PM) and technically premixed (TPM). A new multi-resolution modal decomposition method, using a combination of wavelet transforms and proper orthogonal decomposition (WPOD) is performed on time resolved flow velocity and OHPLIF measurements. Thermoacoustic oscillations are observed in the TPM operating mode alone, indicating that the primary heat release driving mechanism is due to fuel-air ratio oscillations. WPOD results for the 0% H2 TPM case reveals intermittent helical PVC oscillations along with axisymmetric hydrodynamic flow oscillations due to the thermoacoustic oscillations. These oscillations cause local flame extinction near the nozzle centrebody resulting in liftoff. A precessing vortex core (PVC) then develops in the flow and enables intermittent flame reattachment. In the 0% H2 premixed case, the flame remains lifted off the centrebody despite the presence of PVC oscillations. H2 enrichment results in the suppression of flame lift-off and the PVC in both operating modes. We show from flow strain rate statistics and extinction strain rate calculations that the increase of the latter with H2 addition, allows the flame to stabilize in the region near the centrebody where the pure CH4 cases show lift off.

Open-Loop Control of the Precessing Vortex Core in a Swirl-Stabilized Combustor: Impact on Flame Shape and Flame Stability

2018 ◽  
Author(s):  
Finn Lückoff ◽  
Moritz Sieber ◽  
Kilian Oberleithner
Keyword(s):  
Vortex Core ◽  
Open Loop ◽  
Time Resolved ◽  
Loop Control ◽  
Precessing Vortex Core ◽  
Flame Dynamics ◽  
Combustion Properties ◽  
Flame Shape ◽  
Lift Off ◽  
The Impact

In this study, we apply periodic flow excitation of the PVC at the centerbody of a generic swirl-stabilized combustor to investigate the impact of the precessing vortex core (PVC) on flame shape and flame dynamics. Previous studies revealed considerable influence of the PVC on combustion properties such as flame dynamics and fuel/air mixing. We employ time-resolved OH*-chemiluminescence and pressure measurements to investigate the influence of the PVC on flame dynamics and flame shape transition. The PVC is typically present in flames which are detached from the burner outlet. This lift-off is observed for increasingly lean mixtures in this study. With the help of the PVC actuation, studied in this work, the transition point between attached and detached flame is shifted towards richer mixtures. Moreover, the dynamics of heat release rate fluctuations that are related to PVC and thermoacoustic instabilities are extracted from the OH*-chemiluminescence data. This reveals a considerable damping of the thermoacoustic oscillations due to the PVC actuation under technically premixed conditions and the rise of additional modes due to the interaction of both dynamics.

Sign in / Sign up

Export Citation Format

Share Document