Empirical mode decomposition applied to planar and volumetric velocity field measurements of a supersonic separated flow

Empirical Mode Decomposition;Tomographic Particle Image Velocimetry;Stereoscopic Particle Image Velocimetry;Particle Image Velocimetry;Fluid Mechanics;Turbulent Structures

Koll, Matthew David ; Dutton ; J. Craig ; Elliott ; Gregory S.

关键词: Empirical Mode Decomposition;    Tomographic Particle Image Velocimetry;    Stereoscopic Particle Image Velocimetry;    Particle Image Velocimetry;    Fluid Mechanics;    Turbulent Structures;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/101632/KOLL-THESIS-2018.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The supersonic separated flowfield aft of a blunt-faced cylinder aligned with the freestream is highly complex such that a technique able to identify instantaneous turbulent structure within it is valuable.In this study, multi-dimensional extensions of fast and adaptive empirical mode decomposition (FAEMD) are implemented on both three-component planar and volumetric velocity fields of a Mach 2.5 supersonic base flow which were obtained using particle image velocimetry.The resulting two-dimensional intrinsic mode functions reveal the various length scales associated with different regions of the flowfield.Coherent streamwise-oriented structures of different scales were detected throughout the flowfield that indicate the presences of quasi-streamwise vortices.The presence of sharply angled structures, at about 45º to the local flow direction, suggests that both conventional- and counter-hairpin vortices are present within the flowfield, especially in the recompression zone and trailing wake.An autocorrelation analysis of the two-dimensional modes revealed the average size, orientation and shape of these different structures.The autocorrelation revealed that the largest flow structures reside in the shear layer due to the elongated nature of these structures in this region. The three-dimensional spatial analysis of this flowfield resulted in the identification of small-scale and large-scale instantaneous turbulent structures.Quasi-streamwise vortices and hairpin vortices were found during the three-dimensional analysis, in both the shear layer and the trailing wake.Linear stochastic estimation of these three-dimensional results revealed the presence of conventional hairpin and counter-hairpin vortices within the shear layer.