Measured and LES Motored-Flow Kinetic Energy Evolution in the TCC-III Engine 2018-01-0192
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.
The measured and simulated kinetic-energy intra-cycle evolution had the same general trends. However, LES underestimated both the kinetic energy ensemble averaged and CCV range during the intake and compression strokes. The underestimation continued until just prior to TDC, where MBT spark timing would have occurred had the engine been fired. Investigation into the kinetic energy CCV distributions were skewed toward much larger values. However, during the expansion stroke the simulation overestimated the measured kinetic energy in the azimuthal plane.