Faculty Advisor

Claudia Fajardo-Hansford

Department

Mechanical and Aerospace Engineering

Presentation Date

4-13-2017

Document Type

Poster

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 operating strategies to improve engine efficiency. The NWR in IC engines is fundamentally different from the canonical steady-state turbulent boundary layers (BL), which have been extensively researched. Motivated by this need, this poster 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, determined at multiple distances from the wall and piston positions. It is hypothesized that the turbulence in IC engine near-wall-layers is created by both wall-shear (as in canonical BL flows) and dissipation of large-scale core-flow turbulence. In contrast to the canonical description of turbulent boundary layers, the normalized velocity profile lacks a well-defined log-law region and does not scale with the wall shear stress. Smaller flow structures in the two-dimensional velocity fields are apparent as the wall is approached, suggesting that turbulence dissipation in the core flow reaches the near-wall layer. A roll-off in correlation strength is consistently observed in the 10 < y+ < 20 region, suggesting that two-point velocity correlations may provide an additional metric for estimating the boundary layer thickness in engine flows.

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