Impact of non-symmetric confinement on the flame dynamics of a lean-premixed swirl flame

The effects of Nanosecond Repetitively Pulsed (NRP) plasma discharges on the dynamics of a swirl-stabilized lean premixed flame are investigated experimentally. Voltage pulses of 8-kV amplitude and 10-ns duration are applied at a repetition rate of 30 kHz. The average electric power deposited by the plasma is limited to 40 W, corresponding to less than 1 % of the thermal power of 4 kW released by the flame. The investigation is carried out with a dedicated experimental setup that allows for studies of the flame dynamics with applied plasma discharges. A loudspeaker is used to perturb the flame acoustically, and the discharges are generated between a central pin electrode and the rim of the injection tube. Velocity and CH* chemiluminescence signals are used to determine the flame transfer function assuming that plasma discharges do not affect the correlation between CH* emission and heat release rate fluctuations. Phase-locked images of the CH* emission were recorded to assess the effect of the plasma on the oscillation of the flame. The results show a strong influence of the NRP discharges on the flame response to acoustic perturbations, thus opening interesting perspectives for combustion control. An interpretation of the modifications observed in the transfer function of the flame is proposed by taking into account the thermal and chemical effects of the discharges. It is then demonstrated that by applying NRP discharges at unstable conditions, the oscillation amplitudes can be reduced by an order of magnitude, thus effectively stabilizing the system.

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

Fluids ◽

10.3390/fluids6030128 ◽

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.

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