Broadband reconstruction of inhomogeneous turbulence using spectral proper orthogonal decomposition and Gabor modes

Ghate, Aditya S.; Towne, Aaron; Lele, Sanjiva K.

doi:10.1017/jfm.2020.78

Cited by 27 publications

(19 citation statements)

References 20 publications

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“…2020) flows, (iv) flow reconstruction (Nekkanti & Schmidt 2021) and low-order modelling (Chu & Schmidt 2021), (v) wakes of actuator disks in turbulent environments (Ghate et al. 2018; Ghate, Towne & Lele 2020), etc.…”

Section: Introductionmentioning

confidence: 99%

Analysis of coherence in turbulent stratified wakes using spectral proper orthogonal decomposition

2022

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We use spectral proper orthogonal decomposition (SPOD) to extract and analyse coherent structures in the turbulent wake of a disk at Reynolds number $ {\textit {Re}} = 5 \times 10^{4}$ and Froude numbers $ {\textit {Fr}} = 2$ , 10. We find that the SPOD eigenspectra of both wakes exhibit a low-rank behaviour and the relative contribution of low-rank modes to total fluctuation energy increases with $x/D$ . The vortex shedding (VS) mechanism, which corresponds to $ {\textit {St}} \approx 0.11 - 0.13$ in both wakes, is active and dominant throughout the domain in both wakes. The continual downstream decay of the SPOD eigenspectrum peak at the VS mode, which is a prominent feature of the unstratified wake, is inhibited by buoyancy, particularly for $ {\textit {Fr}} = 2$ . The energy at and near the VS frequency is found to appear in the outer region of the wake when the downstream distance exceeds $Nt = Nx/U = 6 - 8$ . Visualizations show that unsteady internal gravity waves (IGWs) emerge at the same $Nt = 6 - 8$ . A causal link between the VS mechanism and the unsteady IGW generation is also established using the SPOD-based reconstruction and analysis of the pressure transport term. These IGWs are also picked up in SPOD analysis as a structural change in the shape of the leading SPOD eigenmode. The $ {\textit {Fr}} = 2$ wake shows layering in the wake core at $Nt > 15$ which is captured by the leading SPOD eigenmodes of the VS frequency at downstream locations $x/D > 30$ . The VS mode of the $ {\textit {Fr}} = 2$ wake is streamwise coherent, consisting of $V$ -shaped structures at $x/D \gtrsim 30$ . Overall, we find that the coherence of wakes, initiated by the VS mode at the body, is prolonged by buoyancy to far downstream. Also, this coherence is spatially modified by buoyancy into horizontal layers and IGWs. Low-order truncations of SPOD modes are shown to efficiently reconstruct important second-order statistics.

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Section: Introductionmentioning

confidence: 99%

Analysis of coherence in turbulent stratified wakes using spectral proper orthogonal decomposition

2022

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“…Rendering can either be done at point locations or a subset of the physical domain without having to evaluate the fields in the entire domain at each simulation time step. This computational efficiency of the algorithm can facilitate its use in applications beyond LES enrichment such as inflow generation as was done recently in Ghate, Towne & Lele (2020).…”

Section: Discussionmentioning

confidence: 83%

Gabor mode enrichment in large eddy simulations of turbulent flow

Ghate

Lele

2020

J. Fluid Mech.

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“…(2008 b ) and, more recently, Ghate et al. (2020). We demonstrate low-rank reconstruction using two approaches.…”

Section: Introductionmentioning

confidence: 95%

“…2018; Pickering et al. 2019; Nekkanti & Schmidt 2021), the wake behind a disk (Johansson, George & Woodward 2002; Johansson & George 2006 a , b ; Tutkun, Johansson & George 2008; Ghate, Towne & Lele 2020; Nidhan et al. 2020), pipe flows (Hellström & Smits 2014; Hellström, Ganapathisubramani & Smits 2015; Hellström, Marusic & Smits 2016; Hellström & Smits 2017) and channel flows (Muralidhar et al.…”

Section: Introductionmentioning

confidence: 99%

Frequency–time analysis, low-rank reconstruction and denoising of turbulent flows using SPOD

Nekkanti

Schmidt

2021

J. Fluid Mech.

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Four different applications of spectral proper orthogonal decomposition (SPOD) are demonstrated on large-eddy simulation data of a turbulent jet. These are: low-rank reconstruction, denoising, frequency–time analysis and prewhitening. We demonstrate SPOD-based flow-field reconstruction using direct inversion of the SPOD algorithm (frequency-domain approach) and propose an alternative approach based on projection of the time series data onto the modes (time-domain approach). We further present a SPOD-based denoising strategy that is based on hard thresholding of the SPOD eigenvalues. The proposed strategy achieves significant noise reduction while facilitating drastic data compression. In contrast to standard methods of frequency–time analysis such as wavelet transform, a proposed SPOD-based approach yields a spectrogram that characterises the temporal evolution of spatially coherent flow structures. A convolution-based strategy is proposed to compute the time-continuous expansion coefficients. When applied to the turbulent jet data, SPOD-based frequency–time analysis reveals that the intermittent occurrence of large-scale coherent structures is directly associated with high-energy events. This work suggests that the time-domain approach is preferable for low-rank reconstruction of individual snapshots, and the frequency-domain approach for denoising and frequency–time analysis.

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Broadband reconstruction of inhomogeneous turbulence using spectral proper orthogonal decomposition and Gabor modes

Cited by 27 publications

References 20 publications

Analysis of coherence in turbulent stratified wakes using spectral proper orthogonal decomposition

Analysis of coherence in turbulent stratified wakes using spectral proper orthogonal decomposition

Gabor mode enrichment in large eddy simulations of turbulent flow

Frequency–time analysis, low-rank reconstruction and denoising of turbulent flows using SPOD

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