Proper Orthogonal Decomposition (POD) offers an approach to quantify cycle-to-cycle variation (CCV) of the flow field inside the internal combustion engine cylinder. POD decomposes instantaneous flow fields (also called snapshots) into a series of orthonormal flow patterns (called POD modes) and the corresponding mode coefficients. The POD modes are rank-ordered by decreasing kinetic energy content, and the low-order, high-energy modes are interpreted as constituting the large-scale coherent flow structure that varies from engine cycle to engine cycle. Various POD-based analysis techniques have thus been proposed to characterize engine flow field CCV using these low-order modes. The validity of such POD-based analyses rests, as a matter of course, on the reliability of the underlying POD results (modes and coefficients). Yet a POD mode can be disproportionately skewed by a single outlier snapshot within a large data set, and an algorithm exists to define and identify such outliers. In this paper, the effects of a candidate outlier snapshot on the results of POD-based conditional averaging and quadruple POD analyses are examined for two sets of crank angle-resolved flow fields on the mid-tumble plane of an optical engine cylinder recorded by high-speed particle image velocimetry. The results with and without the candidate outlier are compared and contrasted. In the case of POD-based conditional averaging, the presence of the outlier scrambles the composition of snapshot subsets that define large-scale flow pattern variations, and thus substantially alters the coherent flow structures that are identified; for quadruple POD, the shape of coherent structures as well as the number of modes to define them are not significantly affected by the outlier.
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ASME 2018 Internal Combustion Engine Division Fall Technical Conference
November 4–7, 2018
San Diego, California, USA
Conference Sponsors:
- Internal Combustion Engine Division
ISBN:
978-0-7918-5198-2
PROCEEDINGS PAPER
Effects of Outlier Flow Field on the Characteristics of In-Cylinder Coherent Structures Identified by POD-Based Conditional Averaging and Quadruple POD
Rui Gao,
Rui Gao
Shanghai Jiao Tong University, Shanghai, China
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Li Shen,
Li Shen
Shanghai Jiao Tong University, Shanghai, China
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Kwee-Yan Teh,
Kwee-Yan Teh
Shanghai Jiao Tong University, Shanghai, China
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Penghui Ge,
Penghui Ge
Shanghai Jiao Tong University, Shanghai, China
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Fengnian Zhao,
Fengnian Zhao
Shanghai Jiao Tong University, Shanghai, China
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David L. S. Hung
David L. S. Hung
Shanghai Jiao Tong University, Shanghai, China
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Rui Gao
Shanghai Jiao Tong University, Shanghai, China
Li Shen
Shanghai Jiao Tong University, Shanghai, China
Kwee-Yan Teh
Shanghai Jiao Tong University, Shanghai, China
Penghui Ge
Shanghai Jiao Tong University, Shanghai, China
Fengnian Zhao
Shanghai Jiao Tong University, Shanghai, China
David L. S. Hung
Shanghai Jiao Tong University, Shanghai, China
Paper No:
ICEF2018-9561, V001T03A004; 11 pages
Published Online:
January 3, 2019
Citation
Gao, R, Shen, L, Teh, K, Ge, P, Zhao, F, & Hung, DLS. "Effects of Outlier Flow Field on the Characteristics of In-Cylinder Coherent Structures Identified by POD-Based Conditional Averaging and Quadruple POD." Proceedings of the ASME 2018 Internal Combustion Engine Division Fall Technical Conference. Volume 1: Large Bore Engines; Fuels; Advanced Combustion. San Diego, California, USA. November 4–7, 2018. V001T03A004. ASME. https://doi.org/10.1115/ICEF2018-9561
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