Sensor-based estimation of the velocity in the wake of a low-aspect-ratio pyramid

Hosseini, Zahra; Martinuzzi, Robert J.; Noack, Bernd R.

doi:10.1007/s00348-014-1880-8

Cited by 43 publications

(46 citation statements)

References 24 publications

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“…The most energetic mode (not inspected here) corresponds to a low-frequency, large-wavelength fluctuation, as indicated by the SPOD. Such slow changes of the mean flow are usually called shift modes (Luchtenburg et al 2009;Hosseini et al 2015). In this particular case the shift mode stems from weak movements of the vortex breakdown bubble.…”

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confidence: 99%

“…In recent extensions of linear stochastic estimation, the use of time delays between the different sensors and also the use of one sensor at multiple time instances are pursued to separate periodic coherent structures from turbulent fluctuations (Durgesh & Naughton 2010;Lasagna, Orazi & Iuso 2013). This approach was also used to improve the determination of harmonic POD modes from few pressure sensors (Hosseini, Martinuzzi & Noack 2015). These utilizations of data from various time instances are also related to the temporal constraint used for the POD extension proposed in this article.…”

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confidence: 99%

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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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confidence: 99%

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confidence: 99%

Spectral proper orthogonal decomposition

2016

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“…Note that, while convenient, the mathematical method does not require similarity between POD and temporal Fourier modes. Further improvements to this technique can be achieved by considering the quadratic nature of the relationship between the first pressure (sensor) harmonic and higher velocity harmonics as detailed in [4].…”

Section: Results and Concluding Remarksmentioning

confidence: 99%

Three-Dimensional Instabilities in the Wake of a Wall-Mounted Low-Aspect-Ratio Pyramid

Hosseini

Martinuzzi

2016

Springer Proceedings in Physics

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The turbulent wake dynamics of a wall-mounted low-aspect ratio squarebased pyramid protruding a nominally thin turbulent boundary layer are investigated for a moderate Reynolds number of 28000. The three-component velocity data are measured using planar stereoscopic Particle Image Velocimetry (PIV), from which the coherent global velocity field dynamics are reconstructed using a surface-pressure sensor-based estimation. An estimation technique is implemented which improves on classical EPOD by accounting for phase delay information between the sensor and velocity data. It is shown that the energy exchange between a slow-varying global and harmonic shedding modes characterise the coherent wake dynamics.

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“…R² is a measure of the unresolved fluctuations and has been used for instance by Clark et al [19] and Hosseini et al [20]. It is calculated as follows:…”

Section: Error Criteriamentioning

confidence: 99%

“…In 2015, Hosseini [20] proposed a new approach based on EPOD symmetry decomposition and time-delayed signals to reconstruct the wake of a wall-mounted pyramid. He showed that the use of an orthonormal velocity basis, composed of an antisymmetric part, a slow symmetric contribution and a fast symmetric residual, and multi-time pressure signal reduces its residual by 30-50% compare to a straightforward LSE.…”

Section: Introductionmentioning

confidence: 99%