Data analysis in unsteady turbulent flow measurement (preliminary study of data analysis of turbulent flow in engine cylinder)

Turbulence has a significant effect on the combustion process in an internal combustion engine. It is very important to separate the gas flow in the engine cylinder into turbulence and mean flow. Turbulence is defined as higher frequency components in the gas flow. In this study, some methods of frequency filtering to distinguish the turbulence components in the flow were investigated. The characteristics of four kinds of frequency filtering methods, that is to say, methods using both digital and analog filters of Butterworth types, and running average and stationary time-averaged methods, were compared. These methods were applied to an unsteady jet which was similar to the flow in the engine cylinder, and the turbulence characteristics obtained were discussed.