Characterization of tumbling motion in IC engines by vorticity

In this study the strength of the tumbling vortex flow in internal combustion engines is characterized by the total vorticity flux out of an area enclosed by a zero vorticity circuit, or, equivalently, by the circulation around the circuit, and the intensity of the vortex by the mean vorticity over the enclosed area. Consider the flow in a loop-scavenged two-stroke engine with various curved heads. It is seen that when the cylinder head is highly curved, thus, the tumbling vortex dominates the flow in the cylinder, the mean vorticity gradually increases during compression until about 340° CA, followed by a sharp decline. In the period 310°<CA<340° the increasing rate becomes high. This behavior is closely related to the variation of turbulence, being generated as the tumbling vortex is compressed by the piston.