The time-resolved natural flow field of a fluidic oscillator

Woszidlo, Rene; Ostermann, Florian; Nayeri, Christian Navid; Paschereit, Christian Oliver

doi:10.1007/s00348-015-1993-8

Cited by 83 publications

(54 citation statements)

References 17 publications

(29 reference statements)

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“…As already presented in many of the studies on FO, see for example [17][18][19][21][22][23]32], the MC and FC internal flow configuration along a complete oscillation period was divided in several equally spaced time steps. In the present study, the streamlines and pressure contour plots at Reynolds number 16,034 are divided into six time steps, which correspond to 1/6 of a typical oscillation period.…”

Section: Original Fluidic Oscillator At Reynolds Number 16034mentioning

confidence: 99%

“…From their applications in flow control, it is interesting to mention their use in combustion control [3], flow deflection and mixing enhancement [4], flow separation modification in airfoils [5], boundary layer modification on hump diffusers used in turbomachinery [6], flow separation control on compressors stator vanes [7], gas turbine cooling [8], drag reduction on lorries [9], and noise reduction in cavities [10].Despite the existence of particular fluidic oscillator configurations, like the one introduced by Uzol and Camci [11], which was based on two elliptical cross-sections placed transversally and an afterbody located in front of them, or the one proposed by Huang and Chang [12], which was a V-shaped fluidic oscillator, most of the recent studies on oscillators focused on two main, very similar, canonical geometries, which Ostermann et al [13] called the angled and the curved oscillator geometries. Some very recent studies on the angled geometry are [13][14][15][16][17][18][19][20][21][22][23], while the curved geometry was studied by [4,10,13,[23][24][25][26][27][28][29][30][31][32][33]. Ostermann et al [13], compared both geometries, concluding that the curved one was energetically the most efficient.One of the first analyses of the internal flow on an angled fluidic oscillator was undertaken by Bobusch et al [17].…”

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confidence: 99%

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Analysis of the Forces Driving the Oscillations in 3D Fluidic Oscillators

Baghaei

Bergadà

2019

Energies

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One of the main advantages of fluidic oscillators is that they do not have moving parts, which brings high reliability whenever being used in real applications. To use these devices in real applications, it is necessary to evaluate their performance, since each application requires a particular injected fluid momentum and frequency. In this paper, the performance of a given fluidic oscillator is evaluated at different Reynolds numbers via a 3D-computational fluid dynamics (CFD) analysis. The net momentum applied to the incoming jet is compared with the dynamic maximum stagnation pressure in the mixing chamber, to the dynamic output mass flow, to the dynamic feedback channels mass flow, to the pressure acting to both feedback channels outlets, and to the mixing chamber inlet jet oscillation angle. A perfect correlation between these parameters is obtained, therefore indicating the oscillation is triggered by the pressure momentum term applied to the jet at the feedback channels outlets. The paper proves that the stagnation pressure fluctuations appearing at the mixing chamber inclined walls are responsible for the pressure momentum term acting at the feedback channels outlets. Until now it was thought that the oscillations were driven by the mass flow flowing along the feedback channels, however in this paper it is proved that the oscillations are pressure driven. The peak to peak stagnation pressure fluctuations increase with increasing Reynolds number, and so does the pressure momentum term acting onto the mixing chamber inlet incoming jet.Original fluidic oscillators design goes back to the 60 s and 70 s. Their outlet frequency ranges from several Hz to KHz and the flow rate is usually of a few dm 3 /min. From their applications in flow control, it is interesting to mention their use in combustion control [3], flow deflection and mixing enhancement [4], flow separation modification in airfoils [5], boundary layer modification on hump diffusers used in turbomachinery [6], flow separation control on compressors stator vanes [7], gas turbine cooling [8], drag reduction on lorries [9], and noise reduction in cavities [10].Despite the existence of particular fluidic oscillator configurations, like the one introduced by Uzol and Camci [11], which was based on two elliptical cross-sections placed transversally and an afterbody located in front of them, or the one proposed by Huang and Chang [12], which was a V-shaped fluidic oscillator, most of the recent studies on oscillators focused on two main, very similar, canonical geometries, which Ostermann et al. [13] called the angled and the curved oscillator geometries. Some very recent studies on the angled geometry are [13][14][15][16][17][18][19][20][21][22][23], while the curved geometry was studied by [4,10,13,[23][24][25][26][27][28][29][30][31][32][33]. Ostermann et al. [13], compared both geometries, concluding that the curved one was energetically the most efficient.One of the first analyses of the internal flow on an angled fluidic oscillator was undertaken by B...

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Section: Original Fluidic Oscillator At Reynolds Number 16034mentioning

confidence: 99%

mentioning

confidence: 99%

Analysis of the Forces Driving the Oscillations in 3D Fluidic Oscillators

Baghaei

Bergadà

2019

Energies

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“…These devices are used for active flow control applications, where the sweeping motion of the jet allows a much wider actuator spacing, resulting in less energy consumption (Woszidlo et al 2014). The data presented here stem from an experimental set-up investigating the spreading and entrainment of sweeping jets (Ostermann et al 2015b;Woszidlo et al 2015). The data are recorded at a Reynolds number of 37 000 based on the nozzle diameter D and the mean velocity in the nozzle.…”

Section: Fluidic Oscillatormentioning

confidence: 99%

Spectral proper orthogonal decomposition

2016

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The identification of coherent structures from experimental or numerical data is an essential task when conducting research in fluid dynamics. This typically involves the construction of an empirical mode base that appropriately captures the dominant flow structures. The most prominent candidates are the energy-ranked proper orthogonal decomposition (POD) and the frequency-ranked Fourier decomposition and dynamic mode decomposition (DMD). However, these methods are not suitable when the relevant coherent structures occur at low energies or at multiple frequencies, which is often the case. To overcome the deficit of these 'rigid' approaches, we propose a new method termed spectral proper orthogonal decomposition (SPOD). It is based on classical POD and it can be applied to spatially and temporally resolved data. The new method involves an additional temporal constraint that enables a clear separation of phenomena that occur at multiple frequencies and energies. SPOD allows for a continuous shifting from the energetically optimal POD to the spectrally pure Fourier decomposition by changing a single parameter. In this article, SPOD is motivated from phenomenological considerations of the POD autocorrelation matrix and justified from dynamical systems theory. The new method is further applied to three sets of PIV measurements of flows from very different engineering problems. We consider the flow of a swirl-stabilized combustor, the wake of an airfoil with a Gurney flap and the flow field of the sweeping jet behind a fluidic oscillator. For these examples, the commonly used methods fail to assign the relevant coherent structures to single modes. The SPOD, however, achieves a proper separation of spatially and temporally coherent structures, which are either hidden in stochastic turbulent fluctuations or spread over a wide frequency range. The SPOD requires only one additional parameter, which can be estimated from the basic time scales of the flow. In spite of all these benefits, the algorithmic complexity and computational cost of the SPOD are only marginally greater than those of the snapshot POD.

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“…A linear regression line emphasizes the linear dependency between the oscillation frequency and the jet velocity. This linear dependency is a consequence of the oscillator's internal flow dynamics, which is discussed in detail by Woszidlo et al (2015). The linear relationship is limited to the subsonic flow regime as it is present for all supply rates in this study.…”

Section: Relationship Between Velocity Ratio and Strouhal Numbermentioning

confidence: 76%

“…One type of a fluidic oscillator, similar to that used in this study for generating a spatially oscillating jet, is shown in figure 2. More details on the working principle of this design of fluidic oscillators are provided by Woszidlo et al (2015) and Sieber et al (2016). It is noteworthy that several modifications of this concept exist.…”

Section: Introductionmentioning

confidence: 99%

The interaction between a spatially oscillating jet emitted by a fluidic oscillator and a cross-flow

et al. 2019

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This experimental study investigates the fundamental flow field of a spatially oscillating jet emitted by a fluidic oscillator into an attached cross-flow. Dominant flow structures, such as the jet trajectory and dynamics of streamwise vortices, are discussed in detail with the aim of understanding the interaction between the spatially oscillating jet and the cross-flow. The oscillating jet is ejected perpendicular to the cross-flow. A moveable stereoscopic particle image velocimetry (PIV) system is employed for the plane-by-plane acquisition of the flow field. The three-dimensional, time-resolved flow field is obtained by phase averaging the PIV results based on a pressure signal from inside the fluidic oscillator. The influence of velocity ratio and Strouhal number is assessed. Compared to a common steady wall-normal jet, the spatially oscillating jet penetrates to a lesser extent into the cross-flow’s wall-normal direction in favour of a considerable spanwise penetration. The flow field is dominated by streamwise-oriented vortices, which are convected downstream at the speed of the cross-flow. The vortex dynamics exhibits a strong dependence on the Strouhal number. For small Strouhal numbers, the spatially oscillating jet acts similar to a vortex-generating jet with a time-dependent deflection angle. Accordingly, it forms time-dependent streamwise vortices. For higher Strouhal numbers, the cross-flow is not able to follow the motion of the jet, which results in a quasi-steady wake that forms downstream of the jet. The results suggest that the flow field approaches a quasi-steady behaviour when further increasing the Strouhal number.

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The time-resolved natural flow field of a fluidic oscillator

Abstract: the results infer that the jet's oscillation pattern is approximately sinusoidal with comparable residence and switching times.

Cited by 83 publications

References 17 publications

Analysis of the Forces Driving the Oscillations in 3D Fluidic Oscillators

Analysis of the Forces Driving the Oscillations in 3D Fluidic Oscillators

Spectral proper orthogonal decomposition

The interaction between a spatially oscillating jet emitted by a fluidic oscillator and a cross-flow

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