The Proper Orthogonal Decomposition, wavelets and modal approaches to the dynamics of coherent structures

1994 ◽  
Vol 53 (3-4) ◽  
pp. 321-338 ◽  
Author(s):  
Gal Berkooz ◽  
Juan Elezgaray ◽  
Philip Holmes ◽  
John Lumley ◽  
Andrew Poje
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Coherent Structures ◽  
Orthogonal Decomposition ◽  
Proper Orthogonal

Analysis of Coherent Structures in the Far-Field Region of an Axisymmetric Free Jet Identified Using Particle Image Velocimetry and Proper Orthogonal Decomposition

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
A.-M. Shinneeb ◽  
R. Balachandar ◽  
J. D. Bugg
Keyword(s):  
Particle Image Velocimetry ◽  
Proper Orthogonal Decomposition ◽  
Coherent Structures ◽  
Particle Image ◽  
Axial Direction ◽  
Orthogonal Decomposition ◽  
Far Field ◽  
Field Region ◽  
Image Velocimetry ◽  
Proper Orthogonal

This paper investigates an isothermal free water jet discharging horizontally from a circular nozzle (9mm) into a stationary body of water. The jet exit velocity was 2.5m∕s and the exit Reynolds number was 22,500. The large-scale structures in the far field were investigated by performing a proper orthogonal decomposition (POD) analysis of the velocity field obtained using a particle image velocimetry system. The number of modes used for the POD reconstruction of the velocity fields was selected to recover 40% of the turbulent kinetic energy. A vortex identification algorithm was then employed to quantify the size, circulation, and direction of rotation of the exposed vortices. A statistical analysis of the distribution of number, size, and strength of the identified vortices was carried out to explore the characteristics of the coherent structures. The results clearly reveal that a substantial number of vortical structures of both rotational directions exist in the far-field region of the jet. The number of vortices decreases in the axial direction, while their size increases. The mean circulation magnitude is preserved in the axial direction. The results also indicate that the circulation magnitude is directly proportional to the square of the vortex radius and the constant of proportionality is a function of the axial location.

Advanced Identification of Coherent Structures in Swirl-Stabilized Combustors

2016 ◽  
Author(s):  
Moritz Sieber ◽  
Christian Oliver Paschereit ◽  
Kilian Oberleithner
Keyword(s):  
Heat Release ◽  
Proper Orthogonal Decomposition ◽  
Coherent Structures ◽  
High Speed ◽  
Low Frequency ◽  
Orthogonal Decomposition ◽  
Time Resolved ◽  
Operation Conditions ◽  
Natural Dynamics ◽  
Proper Orthogonal

We present an application of a newly introduced method to analyze the time-resolved experimental data from the flow field of a swirl-stabilized combustor. This method is based on classic proper orthogonal decomposition (POD) extended by a temporal constraint. The filter operation embedded in this method allows for continuous fading from the classic POD to the Fourier mode decomposition. This new method — called spectral proper orthogonal decomposition (SPOD) — allows for a clearer separation of the dominant mechanisms due to a clean spectral separation of phenomena. In this paper, the fundamentals of SPOD are shortly introduced. The actual focus is put on the application to a combustor flow. We analyze high-speed PIV measurements from flow fields in a combustor at different operation conditions. In these measurements, we consider externally actuated, as well as natural dynamics and reveal how the natural and actuated modes interact with each other. As shown in the paper, SPOD provides detailed insight into coherent structures in swirl flames. Two distinct PVC structures are found that are very differently affected by acoustic actuation. The coherent structures are related to heat release fluctuations, which are derived from simultaneously acquired OH* chemiluminescence measurements. Besides the actuated modes, a low frequency mode was found that significantly contribute to the global heat release fluctuations.

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