Example 4: Turbulent Backward-Facing Step

This example studies the turbulent fluid flow within a channel with a backwards-facing step.

This example is based on previous case and the same geometry will be used. Some modifications will be done to the boundary conditions of example 3 in order to show how to study the turbulent fluid flow. The flow pattern will again be calculated using the incompressible Navier-Stokes equations for a Reynolds number of Rn = 70.000. At this regime, turbulence is fully developed (the transitional range lies between 1200 < Rn  < 6600).

The Reynolds number is defined here as: Re = νmax·Hρ / μ, with the characteristic length of the problem, H, being the height of the step. Being vmax the maximum velocity value attained in this section.

The Reynolds number derives from the choice of the following parameters

-         D            =          0.5       m

-         vmax            =          1.0       m/s

-         r             =          1          kg/m3

-         m            =          7.14·10-6          kg/m.s

According to the previous equation we obtain

Re = 70.000

The best way to proceed from example 3 is to save this file with a different name.

Only small changes in the initial and boundary conditions fixed in previous example are required in order to run this problem. Next the necessary changes are described.