Particles in a Periodic Double Shear Layer

Created using ANSYS 15.0

Learning Goals

In this tutorial, you will learn to:

• Some of the fundamental aspects of particulate laden flows
• How to load Load a flow field initial condition from a file using User Defined Function (UDF).
• Use How to use Discrete Phase Model (DPM) to simulate particles in a flow.
• Define How to define particle injection using an injection file / Create injection files using MATLAB codes.
• Visualize How to visualize particle flow in CFD-Post.

Problem Specification

In this tutorial, we study a case of particle laden flows. The purpose is to illustrate some of the complex interactions between the uid fluid phase and a dispersed particle phase using commercially available tools. For this purpose, we study a 2D-periodic double shear layer with disceminated particles disseminated particles as shown bellow:

Figure 1. Initial setup for the problem.

A mixing layer is a flow where two parallel streams flow at different velocities, resulting in a non-zero velocity gradient. In the absence of any perturbation, a mixing layer , for instance a Ux = U tanh(y) profile, diffuses under the action of viscosity to the mean value of top and bottom velocities. On the other hand, specially manufactured oscillations in the shearing layers will lead to the evolution of vorticies. These perturbations must satisfy However, in a real life situation, the flow is subject to random perturbations, which causes it to destabilize and forms vorticies. The most potent perturbation can be computed using the Orr-Sommerfeld equation , otherwise they are suppressed by viscosity[1]. In this tutorial, we provide the Orr-Sommerfeld mode as an initial flow condition containing the Orr-Sommerfeld perturbation in a separate input file.to the flow.

In the presence of particles, the vorticies that result from the unstable perturbations offer interesting interactions with the suspended particlesThe point of having vorticies develop in the flow field, is to observe the interaction of particles with these structures. In a general sense, "light" particles get trapped in the flow vorticies, while "heavier" particles carrying more inertia might get expelled under a corrioliscentrifugal-type effect force from the swirling regions to gather along stretching regions of the flow [2,3]. This effect is known as preferential concentration and is illustrated in the following sketch:[Insert preferential concentration sketch]

Image Added

Figure 2. Preferential concentration mechanism: particles gather along stretching regions and get expelled from vortical regions.

Formal definitions, and a thorough discussion is provided in the Pre-Analysis section.

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