Mass and Momentum Transport Phenomena at Vortex Pairing in a Mixing Layer. Analysis using Direct Numerical Simulation.

Abstract

Mass and momentum transport phenomena in the process of vortex pairing in a spatially developing mixing layer is discussed based on the instantaneous velocity and scalar database obtained from the direct numerical simulation using 4-th order central difference scheme. It was pointed out that, as for the momentum transport, a gradient diffusion is dominant in the first half of pairing process and a counter-gradient diffusion occurs in the latter half process. On the other hand, a gradient diffusion is induced and pronounced for the mass transport in the whole process of vortex merging. A detail mechanism is discussed by analyzing the behavior of u′v′ and v′c′, which respectively represents the momentum and mass transport, in the vortex pairing process.