Experimental study of the internal flow structures inside a fluidic oscillator

Abstract

The internal flow characteristics of a fluidic oscillator were investigated experimentally. Particle image velocimetry and time-resolved pressure measurements were employed in water to visualize and quantify the internal flow patterns. The method of proper orthogonal decomposition was applied to random flow field snap shots for phase reconstruction of one oscillation cycle. The resulting phase-averaged information provides detailed insight into the oscillation mechanism as well as into the interaction between the main chamber of the oscillator and its feedback channels. A growing recirculation bubble between the main jet and the attachment wall is identified as an underlying mechanism that causes the main jet to oscillate. The flow field measurements are complemented by time-resolved pressure measurements at various internal locations which yield additional comprehension of the switching behavior and accompanying timescales. Geometrical features, in particular at the inlet and outlet of the mixing chamber, are found to have a crucial impact on important flow characteristics such as oscillation frequency and jet deflection.Peer ReviewedPostprint (published version

The time-resolved natural flow field of a fluidic oscillator

“…However, the relative impact of either effect cannot be quantified with the existing data set and oscillator geometry. Similar oscillations in the jet's properties were observed by Bobusch et al (2013a) with water as a working fluid. These findings may affect the oscillator's applications, especially if an even distribution of fluid is desired.…”

“…The method of proper orthogonal decomposition was employed to obtain time-resolved information on the internal flow field only. Despite limited temporal and spatial resolution, Bobusch et al (2013a) provided insight into the internal dynamics for the first time. A novel approach to obtaining timeresolved data on a fluidic oscillator with one feedback channel was documented by Wassermann et al (2013) who employed phase-locked three-dimensional threecomponent magnetic resonance velocimetry.…”

“…However, with this system, the oscillations were not controlled by the natural internal dynamics. A design similar to the one utilized in the current study was investigated by Bobusch et al (2013a) with water as a working fluid. Using water lowers the oscillation frequency and exit velocity for a given Reynolds number and circumvents compressibility effects.…”

Investigation of Fluidic Devices for Mixing Enhancement for the Shockless Explosion Combustion Process

“…Since the range of flow rates is defined by the dye pump, the two different oscillators were manufactured with 3 different aspect ratios each. From literature, it is known that the frequency of these oscillators scales linearly with the volumetric flow rate [14,17]. Accordingly, the dependency of the frequency on the jet in crossflow momentum ratio J is of quadratic nature.…”

“…From literature [11], it is known that these devices can enhance the spa- tial mixing, especially close to the injection position. The oscillatores used were described in detail in [14]. The oscillatory parameters of these devices were determined by numerical simulations, which were carried out with a validated numerical model [15].…”