Investigation of Combustion Control in a Dump Combustor Using the Feedback Free Fluidic Oscillator

A feedback free fluidic oscillator was designed and integrated into a single element rocket combustor with
the goal of suppressing longitudinal combustion instabilities. The fluidic oscillator uses internal fluid dynamics
to create an unsteady outlet jet at a specific frequency. An array of nine fluidic oscillators was tested to mimic
modulated secondary oxidizer injection into the combustor dump plane. The combustor has a coaxial injector
that uses gaseous methane and decomposed hydrogen peroxide with an overall O/F ratio of 11.7. A sonic
choke plate on an actuator arm allows for continuous adjustment of the oxidizer post acoustics enabling the
study of a variety of instability magnitudes. The fluidic oscillator unsteady outlet jet performance is compared
against equivalent steady jet injection and a baseline design with no secondary oxidizer injection. At the
most unstable operating conditions, the unsteady outlet jet saw a 67% reduction in the instability pressure
oscillation magnitude when compared to the steady jet and baseline data. Additionally, computational fluid
dynamics analysis of the combustor gives insight into the flow field interaction of the fluidic oscillators. The
results indicate that open loop high frequency propellant modulation for combustion control can be achieved
through fluidic devices that require no moving parts or electrical power to operate.