Computational Characterization of the Feedback Free Fluidic Oscillator

Abstract

The feedback free fluidic oscillator uses the unsteady nature of two colliding jets to create a single oscillating outlet jet with a wide sweep angle. These devices have the potential to increase mixing in combustion applications and provide additional combustion control. The work presented in this paper uses two-dimensional computational fluid dynamics, CFD, to analyze the jet oscillation frequency over a range of operating conditions and to determine the effect that geometric changes in the oscillator design have on the frequency. In addition, microphone data gathered from six 3D printed fluidic oscillators is used to validate the CFD and correlate the 2D analysis to several oscillator aspect ratios. Results presented in this paper illustrate the changes in jet oscillation frequency with gas type, gas temperature, operating pressure, pressure ratio across the oscillator, aspect ratio of the oscillator, and the frequency trends with various changes to the oscillator geometry.

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

“…with decomposed hydrogen peroxide frequencies compared to the equivalent room temperature nitrogen gas oscillation frequency. 32 The decomposed hydrogen peroxide was simulated using a mixture of 57.65% H 2 O and 42.35% O 2 by mass at the experimentally measured oscillator manifold temperature of 400 • F. The lower density and higher speed of sound give the decomposed peroxide a frequency increase over the room temperature nitrogen gas. The low frequency chamber pressure transducer and the fluidic injector manifold pressure measurements were used to determine the operating pressure ratio for this estimate.…”

“…This trend matches microphone data from prior fluidic oscillator designs and testing. 32 The fluidic oscillator injector supply line was directly connected to the main oxidizer manifold such that the fluidic oscillators were running when the main oxidizer valve was open. Due to the inability to turn the fluidic injectors off in this setup, the results are compared against identical flow rate conditions with the baseline CVRC chamber.…”

“…30 The feedback free fluidic oscillator works at frequencies as low as a few hundred hertz with liquids to over 20 kHz with gaseous fluids with the frequency depending on the geometry, fluid type and density, and the operating pressure ratio. [31][32][33][34][35] Building off of the previously discussed open loop control experiments which found that propellant modulation at frequencies away from the chamber acoustic harmonics suppressed combustion instabilities, the feedback free fluidic oscillator can be tailored to specific frequencies for open loop combustion instability control. This paper describes an experimental study using the feedback free fluidic oscillator for oxidizer flow control to assess performance of the fluidic oscillator.…”