Fluid Dynamics

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 ?=?=0).
4. From question 3 above, select an appropriate grid size, discuss, and justify your selection.

NOTE:
In ANSYS CFX-Pre, you will have to create a new variable/expression, CD as:
2*force_x()@body / (area()@body * massFlowAve(Density)@Inlet * (massFlowAve(Velocity)@Inlet)^2)
Note: You will need to change “body” to whatever you defined your square_body as in named selections. Similarly, for the “Inlet”, please refer to the correct name you defined under named selections.
Submission:
A written report is to be submitted including a short introduction and conclusion (no more than half a page each section). The report should contain a discussion of the points bolded above with evidence to support the discussion together with relevant figures such as figures illustrating the mesh or element distribution, plots of the velocity profiles, contour plots, etc as required.

Comments:
Practical and Technical reports are written IMPERSONAL, PAST TENSE, THIRD PERSON.

Sample Solution