# Documentation du code de simulation numérique SUNFLUIDH

### Outils du site

sunfluidh:sunfluidh_tutorials

# Tutorial : How to build the input data file ?

This tutorial shows how to create an input data file for a 2D heated back-facing step flow. After providing the main features of the problem, explanations on how to build step by step the corresponding data file is shown. Each relevant namelist is commented and referred to other pages for more details.
The user can create its own data file by resorting to any highlighted data set.

## Flow characteristics

### Description

The computation is on a 2D heated back-facing step flow. The temperature of the bottom and top walls is imposed to $T_c$ and the temperature of the step walls is $T_h$. The inflow is fixed with an uniform velocity profile $U_b$ at temperature $Tc$. We consider an incompressible flow under the Boussinesq hypothesis : the physical properties are constant and the thermal buoyancy effect is modelised by the Boussinesq hypothesis : $F_b= -\rho_0.\beta.g_0.(T - T_0)$ (see the page Gravity for more details). We suppose the fluid is air that behaves as a perfect gas. As a consequence, $\beta= \frac{1}{T_0}$

The governing equations for incompressible flows are shown here.

### Dimensionless data

Reference scales for the dimensionless problem :

• the fluid density $\rho_0$
• the bulk velocity $U_b$
• the kinematic viscosity $\mu_0$
• the step height
• the temperature $T_c$

From the previous reference scales, we define the Reynolds number : $Re_h= \frac{\rho_0 \dot U_b \dot h}{\mu_0}$ and the dimensionless temperature $T*= \frac{T}{T_c}$.
We therefore deduce the following dimensionless data :

• Fluid density $\rho_0*=1$
• Inflow bulk velocity $U_b*= 1$
• Bottom and top wall temperature $T_c*=1$
• Thermal expansion coefficient $\beta*=1$
• Step height $h*= 1$

Any other data of the problem are set to :

• Domain length : $L*=12$
• Domain height : $H*= 2$
• Step length : $l*= 2$
• Reynolds number $Re_h= 100$
• Step wall temperature $T_h*= 2$
• Gravity constant $g*= \frac{g_0 \dot h}{U_b^2}= 1$
• Prandtl number $Pr= 0.71$

## Data setup

We now build the data file by selecting the relevant namelists in the lookup list. We only keep the relevant variables (that must be explicitly set). The others ones are removed. We need to set :

Boundary conditions can be difficult to understand. Some help can be find through some examples illustrated here.