NUMRICAL STUDY OF MIXING FOR PULSATILE FLOW IN A TWO-DIMENSIONAL

摘要

The objective of this work is a numerical study of the fluid mixing in the pulsatile flow through the two-dimensional rough wall channel. The rough surface is of the repeated square ribs with the pitch ratio W/h (W and h denote the roughness spacing and height, respectively ). The pulsatile flow is given by the varying flow flux sinusoidally in time. The flow cases for the non-dimensional pulsatile frequency f = 0.1-2.0 and W/h=2, 4 and 8 were calculated at the fixed Reynolds number Re=1000. The ideal particles ( massless and passive ) were introduced in the obtained Eulerian flow field by the numerical solution. From the calculated trajectories of passive particles, the flow pattern was observed near the rough wall region in channel. The advection pattern of particles shows highly complex. It imply to produce chaotic motion of the advection of particles even when the Eulerian flow field is a simple and regular pulsatile flow. Moreover, the motion and deformation of a "blob" in roughness groove shows the stretching and folding of fluid elements in time-periodic flow. It can be supposed that the flow near the rough wall region displays chaotic behavior. In order to further research the mixing process, Poincare sections of the flow and Liapunov exponents in a given flow region were also calculated.