# How to start with a CFD problem?

**Defining the aim**

• Choose the modelling options

- The physical models needed for analysis (i.e. turbulence, heat transfer, compressibility, etc.)

- The simplification assumptions (i.e. steady-state, symmetry, periodicity, etc.)

- Unique modelling capability (i.e. GUI, special features of a code, etc.)

• Choose the degree of accuracy

• Choose how quickly the results are needed

• Decide if CFD is an appropriate tool

**Identifying the domain**

• Decide how to choose the computational domain

- Known boundary conditions and other input data

- Extension of domain to enable comparison with data

• Decide if you can simplify the domain (e.g. 1D, 2D, etc)

Below is one example where you could for instance choose a 2D domain to model the flow or you could go for the 3D domain. In the 3D case, you need to realise that you may not need to account for the whole geometry. Usually a small segment (a 30 degree segment in this case) would be sufficient, provided you use appropriate boundary conditions.