Understanding In-Cylinder Flow Variability Using Large-Eddy Simulations

Abstract

Multi-cycle Large-eddy simulations (LES) of motored flow in an optical engine housed at the University of Michigan have been performed. The simulated flow field is compared against particle image velocimetry (PIV) data in several cutting planes. Circular statistical methods have been sued to isolate the contributions to overall turbulent fluctuations from changes in flow direction or magnitude. High levels of turbulence, as indicated by high velocity root-mean square (RMS) values, exist in relatively large regions of the combustion chamber. But, the circular standard deviation, a measure of the variability in flow direction independent of velocity magnitude, is much more limited to specific regions or points, indicating much of the turbulence is from variable flow magnitude rather than variable flow direction. Using the circular standard deviation is also a promising method to identify critical points, such as vortex centers or stagnation points, within the flow, which may prove useful for future engine designers.