Two-Point Velocity Correlations in the Near-Wall Region of a Reciprocating Internal Combustion Engine.

Paper #:
  • 2017-01-0613

Published:
  • 2017-03-28
Abstract:
Developing a complete understanding of the structure and behavior of the near-wall region (NWR) in reciprocating, internal combustion (IC) engines and of its interaction with the core flow is needed to support the implementation of advanced combustion and engine operation strategies. The NWR in IC engines is fundamentally different from canonical boundary layers, whose structure, similarity and dynamics have been thoroughly documented in the technical literature. Motivated by this need, this paper presents results from the analysis of two-component velocity data measured with particle image velocimetry near the head of a single-cylinder, optical engine. The interaction between the NWR and the core flow was quantified via two-point velocity correlations, computed at multiple distances from the wall and piston positions. The calculations were performed using the standard, single-side approach, as well as a directional approach, in which the starting point of the correlation was progressively moved away from the wall, while sampling the correlations in the wall and piston directions. Both analyses were conducted on instantaneous and Reynolds-decomposed flow fields, enabling the assessment of mean flow effects on the results. Regardless of correlation distance, the correlation strength was found to decay sharply between one and two millimeters, consistent with the estimated thickness of the wall layer. The directional correlations revealed a threshold location at which the decorrelation rate became independent of direction. This location was found to occur farther away from the wall for the wall-normal velocity component, consistent with recent findings that the wall effect on the wall-normal component extends into the core flow.
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