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A primary goal of large eddy simulation, LES, is to capture in-cylinder cycle-to-cycle variability, CCV. This is a first step to assess the efficacy of 35 consecutive computed motored cycles to capture the kinetic energy in the TCC-III engine. This includes both the intra-cycle production and dissipation as well as the kinetic energy CCV. The approach is to sample and compare the simulated three-dimensional velocity equivalently to the available two-component two-dimensional PIV velocity measurements. The volume-averaged scale-resolved kinetic energy from the LES is sampled in three slabs, which are volumes equal to the two axial and one azimuthal PIV fields-of-view and laser sheet thickness. Prior to the comparison, the effects of sampling a cutting plane versus a slab and slabs of different thicknesses are assessed. The effects of sampling only two components and three discrete planar regions is assessed.

Two-dimensional PIV was used to measure the cycle to cycle variability of large-scale flow-structures at TDC in a motored, two-valve, four-stroke engine. Over two hundred velocity distributions were measured for both a highly directed flow using a shrouded valve and a relatively undirected flow using a standard valve. Each cycle of the directed flow had the appearance of the single large swirl structure seen in the ensemble mean. Cyclic variability of the large-scale flow structure was manifest as variations in swirl ratio (rotational speed). Generally the variability was limited to scales smaller than 10 mm in size. For the undirected flow, none of cycles had the appearance of the ensemble mean. The flow appeared to be multimodal in that large-scale flow-structure patterns could be classified into three types based on flow-pattern recognition.

Two-dimensional in-cylinder velocity distributions measured with Particle Image Velocimetry were compared with computed results from Computational Fluid Dynamics codes. A high-swirl, two-valve, four-stroke transparent-combustion-chamber research engine was used. Comparisons were made of mean-flow velocity distributions, swirl-ratio evolution during the intake and compression strokes, and turbulence distributions at top-dead-center compression. This comparison with the measured flows led to more accurate calculations by identifying code improvements including swirl in the residual gas, modeling of the gas exchange during the valve overlap, and improved numerical accuracy.

Particle Image Velocimetry (PIV) was used to make instantaneous velocity measurements over a 24 mm by 32 mm area in a fired two-stroke cycle engine. The unburned-gas regions of the photographs were successfully interrogated adjacent to the flames and with sufficient resolution to resolve the velocity integral-length scales. A highpass filtering algorithm, different from that used in a previous motored-engine study, was implemented to allow for the arbitrary flame boundary. The large-scale vorticity in this study was considerably higher than in a previous study where a different engine was used. The large-scale normal and shear strain-rates distributions revealed only a small increase over those in the previous study, and the magnitude of the vorticity and shearstrain-rate appeared to be larger near the flame. However, the data are too limited to offer general conclusions about the flow.