In recent years it has been demonstrated that direct
microjet injection into the shear layer of the main
jet disrupts the feedback loop inherent in high
speed impinging jet flows, thereby significantly
reducing the adverse effects. The amount of noise
reduced by microjet actuation is known to be
dependent on nozzle operating conditions. In this
book, two active control strategies using microjets
are suggested to maintain a uniform, reliable, and
optimal reduction of these tones over the entire
range of operating conditions.
In order to obtain an optimal performance of the
actuator, a two-mode feedback model that captures
both the low and high-frequency Rossiter mode was
suggested to investigate the role of pulsed microjet
in the feedback loop. Due to the fact that a low
frequency pulsing brought about additional reduction
compared to high frequency pulsing, the presence of
low frequency mode is identified. In the context of
the analytic model, the effect of pulsing is modeled
using a input-shaping controller that accomplishes
noise-reduction through a suitable redistribution of
the acoustic excitation over the high and low
frequencies.
microjet injection into the shear layer of the main
jet disrupts the feedback loop inherent in high
speed impinging jet flows, thereby significantly
reducing the adverse effects. The amount of noise
reduced by microjet actuation is known to be
dependent on nozzle operating conditions. In this
book, two active control strategies using microjets
are suggested to maintain a uniform, reliable, and
optimal reduction of these tones over the entire
range of operating conditions.
In order to obtain an optimal performance of the
actuator, a two-mode feedback model that captures
both the low and high-frequency Rossiter mode was
suggested to investigate the role of pulsed microjet
in the feedback loop. Due to the fact that a low
frequency pulsing brought about additional reduction
compared to high frequency pulsing, the presence of
low frequency mode is identified. In the context of
the analytic model, the effect of pulsing is modeled
using a input-shaping controller that accomplishes
noise-reduction through a suitable redistribution of
the acoustic excitation over the high and low
frequencies.