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Topology and intelligent data analysis
 IDA03 (International Symposium on Intelligent Data Analysis
, 2003
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VISUALIZATION OF MULTISCALE TURBULENT STRUCTURE IN LOBED MIXING JET USING WAVELETS
, 2000
"... vortex, twodimensional orthogonal wavelet transform The twodimensional orthogonal wavelet transform was applied to the LIF image of lobed mixing jet for identifying the multiscale turbulent structures. The digital imaging slice photographs at x/D=16 and 24 with Re=3000 were respectively decompose ..."
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vortex, twodimensional orthogonal wavelet transform The twodimensional orthogonal wavelet transform was applied to the LIF image of lobed mixing jet for identifying the multiscale turbulent structures. The digital imaging slice photographs at x/D=16 and 24 with Re=3000 were respectively decomposed into seven image components with different broader scales. These image components provide visualized information on the multiscale structures in a lobed mixing turbulent jet. The coherent structure and edges of the vortices at different resolutions or scales can be easily extracted. It was found that the scale range of the coherent structure becomes small along the downstream direction, and the size of the intermediateand smallscale structures does not vary significantly with downstream distance.
On coherent structures in a separated/reattached flow
"... Abstract: It is well known that largescale organised motions, usually called coherent structures, exist in many transitional and turbulent flows. The topology and range of scales of coherent structures change widely in different flows. However, it is not well established what kind of largescale co ..."
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Abstract: It is well known that largescale organised motions, usually called coherent structures, exist in many transitional and turbulent flows. The topology and range of scales of coherent structures change widely in different flows. However, it is not well established what kind of largescale coherent structures exists in separated/reattached transitional flows. Large Eddy Simulation (LES) with a dynamic subgridscale model is employed to investigate a separated boundary layer transition under 2 % free stream turbulence level and without free stream turbulence on a flat plate with a blunt leading edge. Flow visualization is employed to show the entire transition process leading to breakdown to turbulence and largescale coherent structures have been identified at various stages of the transition process. However, there are some noticeable difference between the flow case with and without free stream turbulence. The KelvinHelmholtz rolls, which are clearly visible under no free stream turbulence (NFST), are not so clearly visible under 2 % free steam turbulence (FST) case. The Lambdashaped vortical structures which can be clearly seen in the NFST case can hardly be identified in the FST case. Generally speaking, the effects of freestream turbulence have led to an early breakdown of the separated boundary layer and hence increased the randomisation in the vortical structures, degraded the spanwise coherence of those largescale structures. KeyWords: Largeeddy simulation; largescale coherent structures; free stream turbulence; transition 1
INVESTIGATION OF THE ROTATING STALL IN A CENTRIFUGAL COMPRESSOR
"... ABSTRACT Instability of the compressor operation is manifested in two forms: by mild or deep surge. Both of them should be avoided as they lead to reduced performance or serious damage to the machine and its driving system. One of the presurge symptoms is rotating stall that appears mainly in the ..."
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ABSTRACT Instability of the compressor operation is manifested in two forms: by mild or deep surge. Both of them should be avoided as they lead to reduced performance or serious damage to the machine and its driving system. One of the presurge symptoms is rotating stall that appears mainly in the impeller and transfers to other parts of the compressor. This phenomenon can be described as a rotating pressure wave arising and decaying intermittently. Such an irregularly changing object needs an analyzing tool that allows for a spectrum fluctuation study. The authors used the signal timefrequency representation with progressive wavelets to analyze the static pressure signals acquired during a few deep surge cycles. The rotating stall was identified with the crosscorrelation of the continuous wavelet transform. The same method allowed for calculation of the time lag between oscillatory pressure signals coming from the diffuser and the inlet of the compressor, which estimates the reverse flow velocity.
unknown title
, 2007
"... Crosswavelet analysis of wall pressure fluctuations beneath incompressible turbulent boundary layers ..."
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Crosswavelet analysis of wall pressure fluctuations beneath incompressible turbulent boundary layers
Analysis Of Turbulent Structure Using Discrete Wavelet Transform
"... To evaluate coherent structures in the dimension of time and scale, a new procedure based on the multiresolution analysis and multiresolution autocorrelation analysis is developed in this paper. By analyzing u and vcomponents of fluctuating velocity, the coherent structure and its scales can be ..."
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To evaluate coherent structures in the dimension of time and scale, a new procedure based on the multiresolution analysis and multiresolution autocorrelation analysis is developed in this paper. By analyzing u and vcomponents of fluctuating velocity, the coherent structure and its scales can be identified when larger amplitude fluctuation and stronger autocorrelation are appeared at same wavelet level. For a turbulent jet at position of x/d=6, the larger coherent structures with frequency 39Hz can be deduced around times 0.29, 0.53, 0.6 and 0.67s. This also represent the passing of eddies through the shear layer and concentration of the energy of the flow at these instants. Key Words: Discrete Wavelet Transform, Eddy, Jet, Multiresolution Correlation Analysis, Turbulence INTRODUCTION There exist many different elementary structures in turbulent flows. One of important structure is called coherent structure, and it is usually defined as a region of the flow over which at le...
Structure Evaluation Of Unsteady Turbulent Flow With Continuous And Discrete Wavelet Transforms
, 1999
"... To evaluate eddy structures of a plane turbulent jet in the dimension of time and scale, the velocity signals were analyzed using the continuous and discrete wavelet transforms in this paper. From the distribution of coefficients of continuous wavelet transform, localized nearly periodic eddy motion ..."
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To evaluate eddy structures of a plane turbulent jet in the dimension of time and scale, the velocity signals were analyzed using the continuous and discrete wavelet transforms in this paper. From the distribution of coefficients of continuous wavelet transform, localized nearly periodic eddy motions with a=64ms, 100ms and 180ms were respectively observed in the shear layer of x/d=8.5 in the time range of t=0~220ms, 280~600ms and 680~1000ms, although the local scale of motion always changes with time in unsteady turbulent jet. From multiresolution analysis or discrete wavelet transform, the peak that appears in the component of fluctuating velocity represents the passing of eddy through the shear layer and concentration of the energy of the flow at instant. The intermittent eddy phenomenon or zero components of fluctuating velocity can be observed at higher levels or smaller scales. INTRODUCTION The largescale eddy motion in a plane turbulent jet exhibits an symmetric, periodic and ...
Extraction of a Multiscale Structure of a Turbulent Lobed Jet from PIV Results Using a Vector Wavelet Multiresolution Technique
, 2001
"... The waveletbased vector multiresolution technique was applied to the postprocessing of PIV results for identifying the multiscale turbulent structures of a lobed jet. By analyzing the instantaneous streamlines and vorticity fields of various scales, we obtained important information on the multisca ..."
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The waveletbased vector multiresolution technique was applied to the postprocessing of PIV results for identifying the multiscale turbulent structures of a lobed jet. By analyzing the instantaneous streamlines and vorticity fields of various scales, we obtained important information on the multiscale flow structures. The largescale vortices or coherent structures with a central scale of a = 15.36 mm were easily extracted from PIV measurement results. The intermediateand smallscale vortices embedded within the largescale vortices were separated and visualized.
• Wavelet Transform and Wavelet Correlation Function • Applications of Wavelet CrossCorrelation Analysis. Synthetic and Experimental data
"... • Images of the first and second shear modes and the Scholte wave ..."