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.

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

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

Abstract The precessing vortex core is a helically-shaped coherent flow structure that occurs in reacting and non-reacting swirling flows undergoing vortex breakdown. In swirl-stabilized combustors, this flow structure affects important phenomena, such as turbulent mixing and thermoacoustic oscillations. In this work, a flow control system is developed 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 actuator is driven in a closed loop to achieve phase-opposition control of the PVC. The flow control system is characterized from pressure measurements and particle image velocimetry 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. This is a very important requirement 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 budget remains unchanged. The destabilization of other modes, such as the axisymmetric mode, may have some implications on thermoacoustic instability.

Impact of the Precessing Vortex Core on NOx Emissions in Premixed Swirl-Stabilized Flames: An Experimental Study

2020 ◽  
Author(s):  
Finn Lückoff ◽  
Moritz Sieber ◽  
Christian Oliver Paschereit ◽  
Kilian Oberleithner
Keyword(s):  
Flow Control ◽  
Large Scale ◽  
Active Flow Control ◽  
Premixed Flame ◽  
Nox Emissions ◽  
Precessing Vortex Core ◽  
Flame Dynamics ◽  
Swirl Flows ◽  
Active Flow ◽  
The Impact

Abstract The reduction of polluting NOx emission remains a driving factor in the design process of swirl-stabilized combustion systems, to meet strict legislative restrictions. In reacting swirl flows, hydrodynamic coherent structures, such as periodic large-scale vortices in the shear layer, induce zones with increased heat release rate fluctuations in connection with temperature peaks, which lead to an increase of NOx emissions. Such large-scale vortices can be induced by the helical coherent structure known as precessing vortex core (PVC), which influences the flow and flame dynamics of reacting swirl flows under certain operating conditions. We developed an active flow control system, which allows for a targeted actuation of the PVC, to investigate its impact on important combustion properties. In this study, the direct active flow control is used to actuate a PVC of arbitrary frequency and amplitude, which facilitates a systematic study of the impact of the PVC on NOx emissions. In the course of the present work, a perfectly premixed flame, which slightly damps the PVC, is studied in detail. Since the PVC is slightly damped, it can be precisely excited by means of open-loop flow control. In connection with time-resolved OH*-chemiluminescence and stereoscopic PIV measurements, the flame and flow response to PVC actuation as well as the impact of the actuated PVC on flow and flame dynamics are characterized. It turns out that the PVC rolls up the inner shear layer, which results in an interaction of PVC-induced vortices and flame. This interaction considerably influences the measured level of NOx emissions, which grow with increasing PVC amplitude in a perfectly premixed flame. Nearly the same increase is to be seen for a partially premixed flame. This in contrast to previous studies, where the PVC is assumed to reduce the NOx emissions due to vortex-enhanced mixing.

scholarly journals Design of a Fluidic Actuator with Independent Frequency and Amplitude Modulation for Control of Swirl Flame Dynamics

Fluids ◽  
2021 ◽  
Vol 6 (3) ◽  
pp. 128
Author(s):  
Amrit Adhikari ◽  
Thorge Schweitzer ◽  
Finn Lückoff ◽  
Kilian Oberleithner
Keyword(s):  
Flow Control ◽  
Large Scale ◽  
Combustion Process ◽  
Precessing Vortex Core ◽  
Flame Dynamics ◽  
Efficient Combustion ◽  
Control Authority ◽  
Swirl Flame ◽  
Actuator Design ◽  
The Impact

Fluidic actuators are designed to control the oscillatory helical mode, called a precessing vortex core (PVC), which is often observed in gas turbine combustors. The PVC induces large-scale hydrodynamic coherent structures, which can considerably affect flow and flame dynamics. Therefore, appropriate control of this structure can lead to a more stable and efficient combustion process. Currently available flow control systems are designed to control the PVC in laboratory-scale setups. To further develop these systems and find an approach applicable to the industrial scale, a new actuator design based on fluidic oscillators is presented and studied in this paper. This actuator allows for independently adjusting forcing frequency and amplitude, which is necessary to effectively target the dynamics of the PVC. The functionality and flow control of this actuator design are studied based on numerical simulations and experimental measurements. To verify the flow control authority, the actuator is built into a prototype combustor test rig, which allows for investigating the impact of the actuator’s forcing on the PVC at isothermal conditions. The studies conducted in this work prove the desired functionality and flow control authority of the 3D-printed actuator. Accordingly, a two-part stainless steel design is derived for future test conditions with flame.

Impact of the Precessing Vortex Core on NOx Emissions in Premixed Swirl-Stabilized Flames—An Experimental Study

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Finn Lückoff ◽  
Moritz Sieber ◽  
Christian Oliver Paschereit ◽  
Kilian Oberleithner
Keyword(s):  
Flow Control ◽  
Shear Layer ◽  
Vortex Core ◽  
Large Scale ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Premixed Flame ◽  
Nox Emissions ◽  
Precessing Vortex Core ◽  
Flame Dynamics

Abstract The reduction of NOx emissions remains a driving factor in the design process of swirl-stabilized combustion systems, to meet legislative restrictions. In reacting swirl flows, hydrodynamic coherent structures, such as periodic large-scale vortices in the shear layer, induce zones with increased heat release rate fluctuations in connection with temperature peaks, which lead to an increase of NOx emissions. Such large-scale vortices can be induced by the helical coherent structure known as precessing vortex core (PVC), which influences the flow and flame dynamics under certain operating conditions. We developed an active flow control system, allowing for a targeted actuation of the PVC, to investigate its impact on combustion properties such as NOx emissions. In this work, a perfectly premixed flame, which slightly damps the PVC, is studied in detail. Since the PVC is slightly damped, it can be precisely excited by means of open-loop flow control. In connection with time-resolved OH*-chemiluminescence and stereoscopic particle image velocimetry (PIV) measurements, the impact of the actuated PVC on flow and flame dynamics is characterized. It turns out that the PVC rolls up the inner shear layer, which results in an interaction of PVC-induced vortices and flame. This interaction considerably influences the measured level of NOx emissions, which grows with increasing PVC amplitude in a perfectly premixed flame. Nearly, the same increase is measured for partially premixed conditions. This is in contrast to previous studies, where the PVC is assumed to reduce the NOx emissions due to vortex-enhanced mixing.

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.

Object-Oriented Modeling of Intake Air Flow Control System

2001 ◽  
Author(s):  
T. Carlsson ◽  
A. Sokolov ◽  
A. Idebrant ◽  
M. Jirstrand
Keyword(s):  
Control System ◽  
Flow Control ◽  
Air Flow ◽  
Object Oriented ◽  
Flow Control System ◽  
Air Flow Control
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