Experimental and Numerical Study of Swirling ... - Solid Mechanics

Experimental and Numerical Study of Swirling Flow in Scavenging Process for 2-Stroke
Marine Diesel Engines
forced vortex and the axial velocity changes correspondingly from a wakelike
to a jet-like. This change, however, starts at cross-sectional planes close to
cylinder outlet and moves to upstream positions. At 50% port closure, the
mean axial velocity in the whole cylinder attains a jet like profile. The
tangential velocity resembles more to a wall-jet than a forced vortex profile.
With 75% port closure, the jet-like axial velocity profile at cross-sectional
plane close to intake port changes back to wake-like at the adjacent crosssectional
plane and downstream. This indicates a vortex breakdown like
characteristic. The tangential velocity then has forced vortex profile
throughout the cylinder. The non-dimensional profiles of velocity
components have no significant variation with the variation in Reynolds
number.
Numerical simulations are conducted only for the fully open intake port
case. The turbulence models include RNG k and Reynolds stress
models. The simulation results, however, do not show satisfactory
agreement with the experimental data. The models predicted a larger vortex
core size with a reverse flow. The downstream decay in the swirl is predicted
to be lower than observed from experimental results. However, there are
some qualitative features like distribution of modeled Reynolds stress
components that, to some extent, have reasonable agreements. The factors
affecting the performance of the CFD models possibly lie both in the
treatment of turbulence and the numerical aspects.