Sensitivity of a fluidic oscillator to modifications of feedback channel and mixing chamber geometry

Abstract

This experimental study investigates the effects of internal geometry modifications on the performance of a curved Sweeping Jet actuator. The modifications are applied to the geometry of the feedback channel and the mixing chamber Coanda surface, and the resulting actuator properties are evaluated using time-resolved static pressure measurements inside the actuator and hot-wire measurements of the external flow. The major result is that small, localized modifications of the curved sweeping jet actuator geometry can lead to a complete change in the external flow regime, making the jet velocity distribution homogeneous, similar to the angled variant of the actuator. The Coanda surface shape is identified as the primary cause of the external jet adopting the bifurcated or homogeneous flow regime. The relationships between the sweeping frequency, jet deflection angle, required supply pressure, and pressure fluctuations are analyzed and discussed in detail. External flow behavior and coherence are characterized by phase-averaged, phase-locked velocity profiles and auto-correlation of the velocity signals. Graphical abstract

The Influence of Exit Nozzle Geometry on Sweeping Jet Actuator Performance

“…Then, four different shapes with length adjustments were studied to understand the effect on the oscillation frequency and external flow fields, such as the mean flow velocity and pressure distribution of the SWJA. The FFT analysis result showed that the oscillation frequency was not dependent on the external geometry; it varied with the internal geometry as observed in a previous study [26]. However, for the curvature case, the mean velocity downstream of the exit nozzle was 51.98% higher than the baseline at x/h = 5 due to the Coanda effect at the exit nozzle.…”

Raster Angle Impact on Fdm-Based Additive Manufactured Fluidic Oscillator

“…5b depicts the PSDs of 𝑈 ′ (𝑡, 2.36) for 3D printer actuators versus raster angle, for ṁ = 3 g∕s at 𝑥 * = 2.52. The amplitude and definition of the oscillation frequency peaks are directly related to the jet deflection angle [51]. We can note that for printed actuators, the fundamental and first harmonic frequency peaks are not as sharply defined as in the case of the milled sample, more noticeably for raster angles 45 and 90 • .…”

“…Regardless of the surface roughness values and the raster angle, for all printers, the mean velocity profiles feature a bifurcated profile typical for this type of SWJ actuator, albeit with a drastic reduction in jet spreading for 45 and 90 • , more pronounced for 𝑃 90 2 and 𝑃 45 3 . Thus, the raster angle and associated increased surface roughness do not change the jet's external flow regime [51].…”

“…As shown in Fig. 3, we had to shorten the entrance length 𝐿 𝑒 to 9.58 from 19.35 [51]. Therefore, before discussing the performance of the printed actuator, we characterize the milled sample.…”

“…The time-averaged required supply pressure is expressed as 𝑝 𝑠 = 𝑝 𝑖𝑛 −𝑝 ∞ and is often used as an indicator of the actuator's overall energy consumption [51,53]. The standard deviation of 𝑝 𝑠 is less than ±3%, regardless of the mass flow rate.…”