In-cylinder air motion measurements by laser velocimetry under steady state flow conditions

A laser Doppler velocimeter (LDV) has been used to investigate the in-cylinder flow pattern produced in a steady state flow rig by the helical inlet port of a model cylinder head, typical of those used in internal combustion engines. Measurements were taken of the axial and tangential velocity components on four radial axes, at a one bore distance from the cylinder head. The LDV results showed that the axial vortex formed behind the inlet port extends to more than one bore from the cylinder head and the tangential velocity profile is never that of a pure forced vortex. At lower lifts of the valve a smaller contra-rotating swirl was found together with the main swirl pattern, whereas at higher lifts a single swirl was established at the one bore position. Both the tangential and axial fluctuating velocity components were found more uniform than the mean values, with zones of higher turbulence around the flow reversal points corresponding to regions of steep mean velocity gradients. Flow visualization was also used to investigate the flow pattern in the whole cylinder, and hot-wire probes were employed to take advantage of their excellent frequency characteristics in deriving turbulence time scales.