Three dimensional computation of transition to turbulence in a reciprocating engine

A transition to turbulent flow in the compression process of a reciprocating engine is studied by obtaining the finite-difference numerical solutions to the governing Navier-Stokes equations without using explicit turbulence models. A computational method is developed under the assumption that the flow is in a low-subsonic regime with a strong compression. The numerical method is a simple extension of the well-known MAC method. Computations were performed for three different chamber-geometries under the engine speed of 1400 rpm. The present computational results provide convincing evidence to give a direct demonstration of the transient process in which large tumbling vortices break down into smaller sizes near the end of compression process. The present data are found to be in qualitative agreement with the experimental measurements by the Mach-Zehnder interferometry.