活塞发动机湍流研究：统计理论预测量和瞬态湍流的耦合

Planar particle image velocimetry (PIV) and tomographic PIV (TPIV) measurements
are utilized to analyze turbulent statistical theory quantities and the instantaneous
turbulence within a single-cylinder optical engine. Measurements are performed
during the intake and mid-compression stroke at 800 and 1500 RPM. TPIV
facilitates the evaluation of spatially-resolved Reynolds stress tensor (RST) distributions,
anisotropic Reynolds stress invariants, and instantaneous turbulent vortical
structures. The RST analysis describes distributions of individual velocity fluctuation
components that arise from unsteady turbulent flow behavior as well as cycle-to-cycle
variability (CCV). A conditional analysis, for which instantaneous PIV images are
sampled by their tumble center location, reveals that CCV and turbulence have similar
contributions to RST distributions at the mean tumble center, but turbulence
is dominant in regions peripheral to the tumble center. Analysis of the anisotropic
Reynolds stress invariants reveals the spatial distribution of axisymmetric expansion,
axisymmetric contraction, and 3D isotropy within the cylinder. Findings indicate
that the mid-compression flow exhibits a higher tendency toward 3D isotropy than
the intake flow. A novel post-processing algorithm is utilized to classify the geometry
of instantaneous turbulent vortical structures and evaluate their frequency of occurrence
within the cylinder. Findings are coupled with statistical theory quantities to
provide a comprehensive understanding of the distribution of turbulent velocity components,
the distribution of anisotropic states of turbulence, and compare the turbulent
vortical flow distribution that is theoretically expected to what is experimentally
observed. The analyses reveal requisites of important turbulent flow quantities and
discern their sensitivity to the local flow topography and engine operation.