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Multiresolution analysis of density fluctuation in supersonic mixing layer

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Science china(Technological Sciences) 2010年第2期53卷 584-591页

作者： zhao yuxin1. yi shihe, tian lifeng, he lin & cheng zhongyu college of aerospace and material engineering, national university of defense technology, changsha 41.073, china 1. college of aerospace and material engineering National University of Defense Technology Changsha 410073 China

Due to the difficulties in measuring supersonic density field, the multiresolution analysis of supersonic mixing layer based on experimental images is still a formidable challenge. By utilizing the recently developed nanoparticle based planar laser scattering method, the density field of a supersonic mixing layer was measured at high spatiotemporal resolution. According to the dynamic behavior of coherent structures, the multiresolution characteristics of density fluctuation signals and density field images were studied based on Taylor’s hypothesis of space-time conversion and wavelet analysis. The wavelet coefficients reflect the characteristics of density fluctuation signals at different scales, and the detailed coefficients reflect the differences of approximation at adjacent levels. The density fluctuation signals of supersonic mixing layer differ from the periodic sine signal and exhibit similarity to the fractal Koch signal. The similarity at different scales reveals the fractal characteristic of mixing layer flowfield. The two-dimensional wavelet decomposition and reconstruction of density field images extract the approximate and detailed signals at different scales, which effectively resolve the characteristic structures of the flowfield at different scales.

关键词： supersonic mixing layer density fluctuation multiresolution analysis

The fractal measurement of experimental images of supersonic turbulent mixing layer

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Science china(Physics,Mechanics & Astronomy) 2008年第8期51卷 1134-1143页

作者： zhao yuxin yi shihe tian lifeng he lin cheng zhongyu college of aerospace and material engineering National University of Defense TechnologyChangsha 410073China

Flow visualization of supersonic mixing layer has been studied based on the high spatiotemporal resolution Nano-based Planar Laser Scattering(NPLS) method in SML-1 wind tunnel. The corresponding images distinctly reproduced the flow structure of laminar,transitional and turbulent region,with which the fractal measurement can be implemented. Two methods of measuring fractal dimension were introduced and compared. The fractal dimension of the transitional region and the fully developing turbulence region of supersonic mixing layer were measured based on the box-counting method. In the transitional region,the fractal dimension will increase with turbulent intensity. In the fully developing turbulent region,the fractal dimension will not vary apparently for different flow structures,which em-bodies the self-similarity of supersonic turbulence.

关键词： NPLS turbulence mixing layer fractal dimension

A flow control study of a supersonic mixing layer via NPLS

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Science china(Physics,Mechanics & Astronomy) 2009年第12期52卷 2001-2006页

作者： yi shihe he lin zhao yuxin tian lifeng cheng zhongyu college of aerospace and material engineering National University of Defense TechnologyChangsha 410073China

The flow control of a supersonic mixing layer was studied in a supersonic mixing layer wind tunnel with convective Mach number (Mc) at 0.5. The passive control of the mixing layer was achieved by perturbation tapes on the trailing edge of the splitter plate. The control effects of 2D and 3D perturbation tapes with different sizes were compared. The mixing layer was visualized via NPLS,and the transient fine structures were identifiable in NPLS images,which were used to analyze the effects of flow control. The results show that the 2D tapes can enhance the 2D characteristic of the mixing layer,delaying mixing layer transition; and the 3D tapes can enhance the 3D characteristic of the mixing layer,advancing mixing layer transition. 3D structures of the mixing layer were visualized,and the H-type Λ vortexes were found with 3D tapes control.

关键词： supersonic mixing layer NPLS flow control

Study of density field measurement based on NPLS technique in supersonic flow

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Science china(Physics,Mechanics & Astronomy) 2009年第9期52卷 1357-1363页

作者： tian lifeng yi shihe zhao yuxin he lin cheng zhongyu college of aerospace and material engineering National University of Defense TechnologyChangsha 410073China

Due to the influence of shock wave and turbulence, supersonic density field exhibits strongly inhomogeneous and unsteady characteristics. Applying traditional density field measurement techniques to supersonic flows yields three problems: low spatiotemporal resolution, limitation of measuring 3D density field, and low signal to noise ratio (SNR). A new method based on Nano-based Planar Laser Scattering (NPLS) technique is proposed in this paper to measure supersonic density field. This method measures planar transient density field in 3D supersonic flow by calibrating the relationship between density and concentration of tracer particles, which would display the density fluctuation due to the influence of shock waves and vortexes. The application of this new method to density field measurement of supersonic optical bow cap is introduced in this paper, and the results reveal shock wave, turbulent boundary layer in the flow with the spatial resolution of 93.2 μm/pixel. By analyzing the results at interval of 5 μs, temporal evolution of density field can be observed.

关键词： NPLS supersonic density field high spatiotemporal resolution

Density field measurement and approximate reconstruction of supersonic mixing layer

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Chinese Science Bulletin 2010年第19期55卷 2004-2009页

作者： zhao yuxin yi shihe tian lifeng he lin cheng zhongyu college of aerospace and material engineering National University of Defense Technology Changsha 410073 China

The density field measurement of supersonic mixing layer based on the nanoparticle-based planar laser scattering method was *** calibration of experimental images was analyzed,and the relation between tracer particles concentration and local density of flowfield was calibrated with oblique shockwave *** to the characteristic of mixing layer images,the influence of uneven light intensity distribution was *** these calibration methods,the density field of supersonic mixing layer with convective Mach number at 0.12 was *** analyzing the spanwise vortical structures and streamwise density field,the three dimensional(3D) density field was approximately reconstructed,which apparently reflected the 3D structure of supersonic mixing layer.

关键词：超音速混合层密度场测量超声速图像校准实验校准三维结构激光散射法

The experimental study of interaction between shock wave and turbulence

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Chinese Science Bulletin 2007年第10期52卷 1297-1301页

作者： zhao yuxin yi shihe he lin cheng zhongyu tian lifeng college of aerospace and material engineering National University of Defense Technology Changsha 410073 China

The interaction between shock wave and turbulence has been studied in supersonic turbulent mix layer wind tunnel. The interaction between oblique shock wave and turbulent boundary layer and the influence of large vortex in mix layer on oblique shock wave have been observed by NPLS technique. From NPLS image, not only complex flow structure is observed but also time-dependent supersonic flow visualization is realized. The mechanism of interaction between shock wave and turbulence is discussed based on high quality NPLS image.

关键词：激波湍流相互作用实验研究边界层

Supersonic flow imaging via nanoparticles

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Science china(Technological Sciences) 2009年第12期52卷 3640-3648页

作者： zhao yuxin yi shihe tian lifeng cheng zhongyu college of aerospace and material engineering National University of Defense TechnologyChangsha 410073China

Due to influence of compressibility,shock wave,instabilities,and turbulence on supersonic flows, current flow visualization and imaging techniques encounter some problems in high spatiotemporal resolution and high signal-to-noise ratio(SNR)***,nanoparticle based planar laser scattering method(NPLS)is developed *** nanoparticles are used as tracer,and pulse planar laser is used as light source in NPLS;by recording images of particles in flow field with CCD, high spatiotemporal resolution supersonic flow imaging is *** flow-following ability of nanoparticles in supersonic flows is studied according to multiphase flow theory and calibrating experiment of oblique shock *** laser scattering characteristics of nanoparticles are analyzed with light scattering *** results of theoretical and experimental studies show that the dynamic behavior and light scattering characteristics of nanoparticles highly enhance the spatiotemporal resolution and SNR of NPLS,with which the flow field involving shock wave,expansion,Mach disk,boundary layer,sliding-line,and mixing layer can be imaged clearly at high spatiotemporal resolution.

关键词： nanoparticle supersonic flow imaging spatiotemporal resolution signal-to-noise ratio

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