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Abstract
Though the proper orthogonal decomposition (POD) method has been widely adopted in flow analysis, few publications have systematically studied the influence of different POD processing methods on the POD results. This paper investigates the effects of different decomposition regions and decomposition dimensionalities on POD decomposition and reconstruction concerning the tip flow in the compressor cascade. Stereoscopic particle image velocimetry (SPIV) measurements in the blade channel are addressed to obtain the original flow field. Through vortex core identification, development of the tip leakage vortex along the chord is described. Afterwards, each plane is energetically decomposed by POD. Using the identified vortex core center as the geometric center, the effects of different decomposition regions with respect to the vortex core are analyzed. Furthermore, the effects of different single velocity-components as well as their combination are compared. The effect of different decomposition regions on the mode 1 energy fraction mainly impacts the streamwise velocity component. Though the addition of W velocity component in the decomposition does change the spatial structures of high-order modes, it does not change the dynamic results of reconstruction using a finite number of POD modes. UV global analysis is better for capturing the kinetic physics of the tip leakage vortex (TLV) wandering.
Highlights
The efficiency, the pressure rise and the stable operating range are three prominent parameters for energy and power machinery, such as axial fans and compressors
Previous studies showed that these unsteady behaviors have profound effects on the tip leakage flow (TLF) mean characteristics, and a close connection with some important flow phenomena such as rotating stall [9,10], rotating instability [11], oscillations of the tip leakage vortex (TLV) [12] and vortex shedding
Stereoscopic particle image velocimetry (SPIV) has been extensively employed to investigate the characteristics of the TLV for its ability to capture an instantaneous snapshot of tip flow structures at various scales [5,8,13,14]
Summary
The efficiency, the pressure rise and the stable operating range are three prominent parameters for energy and power machinery, such as axial fans and compressors. Besides the simple averaging (ensemble averaging), some researchers employed a triple decomposition to extract the coherent wandering motion from the SPIV data [16] Through this method, the TLV cores are collocated by linearly shifting the instantaneous core positions to the mean vortex core. POD to to analyze analyze the the TLF This organized follows: firstly, experimental apparatus layout are of decomposition dimensionalities the reconstructed field are discussed. This paper paper is is organized as as in follows: firstly, the the flow experimental apparatusIt and and layout that are introduced as follows; secondly, an overview of POD method and vortex core identification is given; findings presented in this paper will inspire other researchers use POD toidentification analyze the TLF. Following parts, the detailed comparison results are analyzed; the last section concludes this work
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