Identification of Coherent Structure Dynamics in Wall-Bounded Sprays using Proper Orthogonal Decomposition

2010 ◽  
Author(s):  
Vinod Narayanan ◽  
Benn Eilers
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Coherent Structure ◽  
Orthogonal Decomposition ◽  
Structure Dynamics ◽  
Proper Orthogonal

Coherent structure in a turbulent jet via a vector implementation of the proper orthogonal decomposition

2007 ◽  
Vol 571 ◽  
pp. 281-326 ◽  
Author(s):  
M. O. IQBAL ◽  
F. O. THOMAS
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Coherent Structure ◽  
Near Field ◽  
Orthogonal Decomposition ◽  
Turbulent Jet ◽  
Mode Number ◽  
Azimuthal Mode ◽  
Proper Orthogonal ◽  
Energy Convergence ◽  
Jet Structure

The coherent structure in the near-field of an axisymmetric turbulent jet at a Reynolds number of 3.8 × 105 and Mach number of 0.3 is experimentally characterized by a vector implementation of the proper orthogonal decomposition (POD). The POD eigenfunctions and associated eigenvalues are extracted at several selected streamwise locations in the initial region. The focus on the near-field is motivated by its importance in numerous technical applications. Results show a rapid energy convergence with POD mode number. Examination of the relative energy contained in the combined azimuthal and radial components of the POD modes reveals that it is comparable to that in the streamwise component. The streamwise evolution of the eigenvalue spectra is characterized by a remarkable variation in the azimuthal mode number energy distribution, leading to the dominance of azimuthal mode m = 1 beyond the end of the jet core. In contrast, a scalar implementation using only the streamwise component shows the dominance of mode m = 2 which is consistent with previous scalar implementations of the POD. For a given azimuthal mode number, the eigenvalue spectra exhibit a broad peak which occurs at a constant value of Strouhal number based on local shear layer momentum thickness and local jet maximum velocity. The phase information required for a local reconstruction of the jet structure is obtained by projecting the POD eigenmodes onto instantaneous realizations of the flow at fixed streamwise locations. The instantaneous realizations are obtained by utilizing cross-stream arrays of multi-sensor probes in conjunction with linear stochastic estimation (LSE). Results clearly show the local dynamic behaviour of each component of the jet structure.

Coherent structure in the turbulent planar jet. Part 1. Extraction of proper orthogonal decomposition eigenmodes and their self-similarity

2000 ◽  
Vol 414 ◽  
pp. 145-194 ◽  
Author(s):  
S. V. GORDEYEV ◽  
F. O. THOMAS
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Strouhal Number ◽  
Coherent Structure ◽  
Orthogonal Decomposition ◽  
Dimensional Structure ◽  
Spanwise Direction ◽  
Self Similarity ◽  
Single Plane ◽  
Planar Jet ◽  
Proper Orthogonal

In this paper the coherent structure in the similarity region of the turbulent planar jet is examined experimentally by application of the proper orthogonal decomposition (POD). In particular, twin cross-stream rakes of X-wire probes are used to take cross-spectral measurements with different spanwise separations between the rakes and at several locations throughout the similarity region. The resulting POD spatial eigenfunctions for each of the three velocity components depend on cross-stream spatial coordinate, Strouhal number, and spanwise wavenumber. Corresponding eigenvalue distributions are obtained in Strouhal number–spanwise wavenumber space. Eigenvalue convergence is demonstrated to be rapid. When properly scaled the eigenfunctions and eigenvalues are shown to exhibit self-similarity though the streamwise location at which this commences depends on the particular velocity component. The results suggest that the flow supports a planar structure aligned in the spanwise direction as well as an essentially three-dimensional structure with asymmetrical shape in the cross-stream direction and pseudo-periodically distributed in the spanwise direction. Comparison of the single- and dual-rake implementations of the POD presented in this paper demonstrate that measurements confined to a single plane are incapable of properly extracting the planar modes. Rather, the single-rake implementation results in modes that appear to be a weighted sum of modes corresponding to different spanwise wavenumbers.

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