Multi-resolution analysis of the large-scale coherent structure in a turbulent separation bubble affected by an unsteady wake

The flow feature of the jet issuing from the circular pipe with the rotating inclined section has been investigated by the method of the flow visualization and the image processing. It has been found that the jet diffusion is affected by the inclined angle and the rotating speed. The coherent structure of the jet has been also studied by using the wavelet multi-resolution analysis. The multi-scale turbulent structures were visualized and the core and edge of the vortex were identified at different broad scales.

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A Visual-Thermal Image Sequence Registration Method Based on Motion Status Statistic Feature Multi-Resolution Analysis

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.267.867 ◽

2011 ◽

Vol 267 ◽

pp. 867-872

Author(s):

Xiu Wei Zhang ◽

Yan Ning Zhang ◽

Jing Zhao

Keyword(s):

Large Scale ◽

Image Sequence ◽

Image Sensor ◽

Difficult Problem ◽

Thermal Image ◽

Registration Method ◽

Multi Resolution Analysis ◽

Sensor Registration ◽

Resolution Analysis ◽

Lm Algorithm

Multi-sensor registration is an important and basic problem of intelligent surveillance. A novel visual-thermal image sequence registration method based on motion statistics feature multi-resolution analysis is proposed. In this method, motion statistics feature is utilized to select corresponding point pairs from visual-thermal synchronous video sequence. Then, multi-resolution analysis of motion statistic feature is done to choose proper scale. Finally, outliners are removed by RANSAC, and the geometry transformation parameters are optimized by LM algorithm. By using motion statistics feature, this method avoids the difficult problem of extracting invariant feature from two different image sensor and doesn’t depend on precise motion detection. Through multi-resolution analysis, the proposed approach can resolve the registration under the change of large scale. The performance was demonstrated on three groups of dataset, the results showed that our algorithm carried out precise image registration under the change of translation, scale and rotation.

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WAVELET MULTI-RESOLUTION ANALYSIS ON LARGE-EDDY SIMULATION OF TURBURLENT FLOW BEHIND A VEHICLE EXERNAL MIRROR

International Journal of Wavelets Multiresolution and Information Processing ◽

10.1142/s0219691313600072 ◽

2013 ◽

Vol 11 (04) ◽

pp. 1360007 ◽

Cited By ~ 7

Author(s):

A. RINOSHIKA ◽

Y. ZHENG ◽

E. SHISHIDO

Keyword(s):

Large Eddy Simulation ◽

Large Scale ◽

Three Dimensional ◽

Wake Flow ◽

Small Scale ◽

Three Dimensional Flow ◽

Eddy Simulation ◽

Multi Resolution Analysis ◽

Large Eddy ◽

Resolution Analysis

The three-dimensional orthogonal wavelet multi-resolution technique was applied to analyze flow structures of various scales around an externally mounted vehicle mirror. Firstly, the three-dimensional flow of mirror wake was numerically analyzed at a Reynolds number of 105 by using the large-eddy simulation (LES). Then the instantaneous velocity and vorticity were decomposed into the large-, intermediate- and relatively small-scale components by the wavelet multi-resolution technique. It was found that a three-dimensional large-scale vertical vortex dominates the mirror wake flow and makes a main contribution to vorticity concentration. Some intermediate- and relatively small-scale vortices were extracted from the LES and were clearly identifiable.

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Three-dimensional wavelet analysis on turbulent structure of dune wake flow

International Journal of Wavelets Multiresolution and Information Processing ◽

10.1142/s0219691315500459 ◽

2015 ◽

Vol 13 (06) ◽

pp. 1550045 ◽

Cited By ~ 3

Author(s):

Yan Zheng ◽

Akira Rinoshika ◽

Shun Fujimoto

Keyword(s):

Coherent Structure ◽

Large Scale ◽

Separation Bubble ◽

Three Dimensional ◽

Turbulent Structure ◽

Wake Flow ◽

Small Scale ◽

Intermediate Scale ◽

Numerical Result ◽

Scale Structures

The three-dimensional (3D) turbulent structure was simulated by large eddy simulation (LES), and then the numerical result was validated by PIV experiment. In order to give a detailed description of dune wake flow, the instantaneous velocity, vorticity, and pressure were decomposed into the large-, intermediate- and relatively small-scale components by 3D wavelet multi-resolution technique. To get a further understanding of coherent structure, the decomposed wavelet components were employed to calculate Q-criterion. It was found that the rollers and horse-shoe structures in the separation bubble were mainly contributed from large-scale structures and it made the most significance to the vorticity concentration. The observations of intermediate-scale horse-shoe structures indicated that the coherent structure was the combined effect of large- and intermediate-scale structures. Besides, from the visualization of 3D streamlines and pressure iso-surfaces, the separation bubble and pressure distribution are found to be dominated by large-scale structure.

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Structure of a turbulent separation bubble

Journal of Fluid Mechanics ◽

10.1017/s002211208300230x ◽

1983 ◽

Vol 137 ◽

pp. 83-113 ◽

Cited By ~ 302

Author(s):

Masaru Kiya ◽

Kyuro Sasaki

Keyword(s):

Surface Pressure ◽

Vortex Structure ◽

Large Scale ◽

Separation Bubble ◽

Pressure Fluctuations ◽

Velocity Fluctuations ◽

Turbulent Separation ◽

Large Scale Vortex ◽

Cross Correlations ◽

The Cross

Flow in the separation bubble formed along the sides of a blunt flat plate with right-angled corners has been studied in terms of extensive single- and two-point measurements of velocity and surface-pressure fluctuations. The cross-correlations between the surface-pressure and velocity fluctuations are found to be useful for the study of large-scale vortex structure in the bubble. Large-scale vortices are shed downstream from the separation bubble with a frequency of about 0.6U∞/xR, where U∞ is the approaching velocity and xR is the time-mean length of the bubble. On top of this regular vortex shedding, there exists a large-scale unsteadiness in the bubble. Vortices which are much larger than the regular vortices are shed with frequencies less than about 0.2U∞/xR. The large-scale unsteadiness is accompanied by enlargement and shrinkage of the bubble and also by a flapping motion of the shear layer near the separation line. The intermittent nature of the flow in the bubble is clarified in some detail. The distributions of the cross-correlations between the pressure and velocity fluctuations demonstrate the vortex structure in the reattaching zone. The longitudinal distance between the vortices is estimated to be (0.7–0.8) xR and their convection velocity is about 0.5U∞ near the reattachment line. The cross-correlations also suggest the existence of a longitudinal counter-rotating system in the bubble. The distance between the axes of the rotation is of the order of 0.6xR. Variations of timescales, lengthscales and phase velocities of the vortices are presented and discussed.

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