Coherent Hydrodynamic Waves and Trailing-edge Noise

Abreu, Leandra I.; Cavalieri, André V. G.; Wolf, William

doi:10.2514/6.2017-3173

Cited by 23 publications

(19 citation statements)

References 25 publications

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“…The resolvent modes in this range are those of interest, as they correspond to activity within the boundary layer. These findings are similar to the observations by Abreu et al 23 in the resolvent analysis of the turbulent boundary layer over an airfoil. Figure 15 shows how the phase speed of perturbations described by the leading SPOD mode have phase speed that varies across the boundary layer.…”

Section: Local Resolvent Analysis Of the Nozzle Mean Flowsupporting

confidence: 92%

“…Wavepackets are clearly present both in the NBL and the jet, indicating a coupling between these two regions. Similar boundary-layer structures have been observed in a turbulent flow over an airfoil by Abreu et al 23 Reliable detection of structures proves to be difficult at low frequencies (e.g. St = 0.2), for which wavelengths exceed the length of the nozzle domain.…”

Section: A Coherent Structures In the Nozzlesupporting

confidence: 72%

“…Correlation coefficient β acquires values between 0 and 1, where β = 1 for a given SPOD mode indicates a satisfactory convergence, i.e the SPOD mode preserves its shape with increasing number of realisations. 23,24 Figure 2 shows the correlation map obtained for varying frequencies. It demonstrates that both 'Jet-Weighted' and 'Nozzle-Weighted' SPOD analyses are reasonably converged as far as the leading modes are concerned, providing values of β larger than 0.8.…”

Section: A Coherent Structures In the Nozzlementioning

confidence: 99%

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Dynamics of turbulent boundary layers exciting wavepackets in subsonic jets

Kaplan

Jordan

Cavalieri

et al. 2019

25th AIAA/CEAS Aeroacoustics Conference

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Section: Local Resolvent Analysis Of the Nozzle Mean Flowsupporting

confidence: 92%

Section: A Coherent Structures In the Nozzlesupporting

confidence: 72%

Section: A Coherent Structures In the Nozzlementioning

confidence: 99%

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Dynamics of turbulent boundary layers exciting wavepackets in subsonic jets

Kaplan

Jordan

Cavalieri

et al. 2019

25th AIAA/CEAS Aeroacoustics Conference

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“…Recent works have explored the connection between SPOD modes and the flow responses to stochastic forcing successfully (Abreu et al 2017;Towne et al 2018;Lesshafft et al 2019). To relate mathematically SPOD and resolvent analysis we can write the relation between the flow realizationsq and the resolvent operator R for a problem with harmonic forcingf asq = Rf .…”

Section: Spod Versus Resolvent Analysismentioning

confidence: 99%

Spectral proper orthogonal decomposition and resolvent analysis of near-wall coherent structures in turbulent pipe flows

et al. 2020

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“…Doing so, the nonlinear forcing is treated as an unknown, and the most amplified flow responses to such forcings are sought. The resolvent operator is then used to extract information from the flow and it has been shown to reproduce relevant features, such as the spectral proper orthogonal decomposition (SPOD) modes of the streamwise velocity fluctuations of a turbulent boundary layer over and airfoil and in a turbulent free jet (Abreu, Cavalieri & Wolf 2017;Towne, Schmidt & Colonius 2018).…”

Section: K Sasaki and Othersmentioning

confidence: 99%

Transfer functions for flow predictions in wall-bounded turbulence

et al. 2019

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Three methods are evaluated to estimate the streamwise velocity fluctuations of a zero-pressure-gradient turbulent boundary layer of momentum-thickness-based Reynolds number up to $Re_{\unicode[STIX]{x1D703}}\simeq 8200$, using as input velocity fluctuations at different wall-normal positions. A system identification approach is considered where large-eddy simulation data are used to build single and multiple-input linear and nonlinear transfer functions. Such transfer functions are then treated as convolution kernels and may be used as models for the prediction of the fluctuations. Good agreement between predicted and reference data is observed when the streamwise velocity in the near-wall region is estimated from fluctuations in the outer region. Both the unsteady behaviour of the fluctuations and the spectral content of the data are properly predicted. It is shown that approximately 45 % of the energy in the near-wall peak is linearly correlated with the outer-layer structures, for the reference case $Re_{\unicode[STIX]{x1D703}}=4430$. These identified transfer functions allow insight into the causality between the different wall-normal locations in a turbulent boundary layer along with an estimation of the tilting angle of the large-scale structures. Differences in accuracy of the methods (single- and multiple-input linear and nonlinear) are assessed by evaluating the coherence of the structures between wall-normally separated positions. It is shown that the large-scale fluctuations are coherent between the outer and inner layers, by means of an interactions which strengthens with increasing Reynolds number, whereas the finer-scale fluctuations are only coherent within the near-wall region. This enables the possibility of considering the wall-shear stress as an input measurement, which would more easily allow the implementation of these methods in experimental applications. A parametric study was also performed by evaluating the effect of the Reynolds number, wall-normal positions and input quantities considered in the model. Since the methods vary in terms of their complexity for implementation, computational expense and accuracy, the technique of choice will depend on the application under consideration. We also assessed the possibility of designing and testing the models at different Reynolds numbers, where it is shown that the prediction of the near-wall peak from wall-shear-stress measurements is practically unaffected even for a one order of magnitude change in the corresponding Reynolds number of the design and test, indicating that the interaction between the near-wall peak fluctuations and the wall is approximately Reynolds-number independent. Furthermore, given the performance of such methods in the prediction of flow features in turbulent boundary layers, they have a good potential for implementation in experiments and realistic flow control applications, where the prediction of the near-wall peak led to correlations above 0.80 when wall-shear stress was used in a multiple-input or nonlinear scheme. Errors of the order of 20 % were also observed in the determination of the near-wall spectral peak, depending on the employed method.

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Coherent Hydrodynamic Waves and Trailing-edge Noise

Cited by 23 publications

References 25 publications

Dynamics of turbulent boundary layers exciting wavepackets in subsonic jets

Dynamics of turbulent boundary layers exciting wavepackets in subsonic jets

Spectral proper orthogonal decomposition and resolvent analysis of near-wall coherent structures in turbulent pipe flows

Transfer functions for flow predictions in wall-bounded turbulence

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