Behavior of Particle Tracers in the Steady and Periodic Wakes of a Circular Cylinder

• Main Authors: Shaswat Saincher, Jyotimay Banerjee
• Format: Article
• Language: English
• Published: Institute of Technology, Nirma University 2000-01-01
• Series: Nirma University Journal of Engineering and Technology
• Online Access: http://nujet.org.in/index.php/nujet/article/view/102

Tracer particles introduced into the flow domain for experimental flow visualization often tend to exhibit chaotic behavior even for the simplest of configurations. These passive tracers do not exactly follow the regime in general. The spatial distributions formed by such particles within the flow field and the probable trajectories followed by them are governed by the phenomenon of Lagrangian chaos. Since the problem at hand has it's foundations in the theories of Hamiltonian dynamics and deterministic chaos, drawing a relation between the Eulerian flow field and the Lagrangian tracer field is a difficult task. However, analyzing this behavior would provide useful insight in interpreting the results of flow visualization experiments which involve particle tracking. Based on this background, the phenomenon of chaotic advection for a laminar cross-flow over a circular cylinder has been investigated numerically. Two configurations are considered, one involving a steady flow at Re=20 while the other characterizing a periodic shedding regime at Re=100. Computational visualization of the flow is carried out by locally injecting neutrally buoyant particles at zero momentum and tracking the same by FLUENT's discrete phase model. The tracks made by the tracers, being equivalent to streaklines, are generated for different injection locations and the trajectories have been compared with the streamline patterns. It has been observed that the steady regime at Re=20 does not exhibit chaotic advection and the streaklines coincide with the streamtraces. On the other hand, the shedding regime, being temporally dependent, depicts a high degree of tracer mixing. The particles tend to form complex spatial distributions in this case. Further, the formation of a particular tracer distribution has been observed to be strongly dependent on the location of the injector within the domain. Since the tracer particles exhibit stochastic behavior for an otherwise simple and periodic underlying flow, it is expected that such patterns can be misleading. A careful study of all possible tracer distributions is hence advisable for visualization of such time dependent flows.