Fluid Dynamics

To carry out a mesh refinement for the given model of a flow over a squared body in a steady laminar flow regime.

ANSYS CFX will be used as it is a commonly utilised CFD software tool

Computational Domain and Boundary conditions

Figure 1: Dimensions of 2D computational domain (not to scale)
The length of the square body, a = 0.01m. The length of the domain upstream the body is 5a, and the length after the body is 14a. The total height of the computational domain is 14*a, and the square body is positioned such that it is centred vertically.
NOTE: 2D simulations will be run. However, as CFX does not allow fully 2D cases, a thickness will be needed. You will have to set the thickness small enough to have quasi-2D simulations.
The boundary conditions are coloured in Figure 1 as follow:

NOTE: The inlet velocity produces a stead-laminar flow, please conduct simulations using laminar conditions. Set the residual target as 1e-06 and the maximum number of iterations as 200.
The fluid flowing through the wind tunnel is water, with the following properties at 20 °C:
Density, ρ= 998 kg/m3
Dynamic viscosity, μ = 1.002 x 10-3 Pa.s
The following activities are to be completed for the assignment

  1. Create the geometry in DesignModeler
  2. Generate different grid sizes of the computational domain in Ansys Mesher including mesh refinements near the square body.
  3. For all grid sizes:
    a. Generate contour plots for the velocity field for each mesh. Compare and discuss qualitative differences between each generated mesh.
    b. Plot the velocity profiles at line B and C (refer Figure 1).
    c. Tabulate the drag coefficient.
    d. Report the formation length (i.e. Length from the rear stagnation point of the bluff body to the start of the wake region (when 𝑈=𝑉=0).
  4. From question 3 above, select an appropriate grid size, discuss, and justify your selection.

Sample Solution