# Tutorial 0 – Freestream

## Freestream

Copy the freestream tutorial folder to your working directory

    cp -r $FLEXI_TUTORIALS/freestream .  The setup considers a freestream scenario with constant pressure$p=101325.0$Pa, density$\rho=1.225$kg/$m^3$and flow vector$\textbf{U}=(1,1,1)^T$m/s. Mesh for tutorial 0. Flow field solution with velocity vector plot of the velocity field. View in$x$-$y$-plane. ### Mesh Generation with HOPR The mesh files used by FLEXI are created by supplying an input file parameter_hopr.ini with the appropriate information.  ./hopr parameter_hopr.ini  This creates the mesh file cartbox_mesh.h5 in HDF5 format. Alternatively, if you do not want to run HOPR, you can also use the provided mesh. ### Flow Simulation with FLEXI The simulation setup is defined in parameter_flexi.ini. The initial condition is selected via the variable vector RefState=(/1.225,1.,1.,1.,101325./) which represents the solution vector$(\rho, u, v, w, p)^T$. FLEXI allows for multiple RefState vectors and numerates them respectively for them to be used by different functions. In this example a single RefState is supplied and therefore is given the number 1. IniRefState = 1 : the initial condition uses RefState 1 for the initial flow field solution. IniExactFunc = 1 : the used exact function routine uses RefState 1, e.g., for the calculation of the$L_2$error norm. Constant flow properties like the gas constant are given in the table below and define the gas behaviour in combination with the ideal gas law$p=\rho R T$. Property Variable Value dynamic viscosity$\mu$mu0 0.000018547 ideal gas constant$R$R 276 isentropic coefficient$\kappa$kappa 1.4 ### Numerical settings The DG solution on the mesh is represented by piecewise polynomials and the polynomial degree in this tutorial is chosen as$N=3\$.

The default settings for these properties are displayed in the table below.

Variable Description Value
N polynomial degree 3
MeshFile cartbox_mesh.h5
tend 1e-6
Analyze_dt 1e-6
nWriteData 1
CFLscale 0.99
DFLscale 0.4

The command

flexi parameter_flexi.ini > std.out


runs the code and dumps all output into the file std.out.
If the run has completed successfully, which should take only a brief moment, the contents of the working folder should look like in this figure below.

Two additional files have been created, which are are named Projectname_State_Timestamp.h5. They contain the solution vector of the conserved variables at each interpolation node at the given time, which corresponds to multiplies of Analyze_dt. If these files are not present, something went wrong during the execution of FLEXI. In that case, check the _std.out_ file for an error message.

After a successful completion, the last lines in this files should look like in this figure:

To visualize the solution, the State-files must be converted into a format suitable for ParaView. Issue the command

convert parameter_convert.ini cartbox_State_000000*.h5


to generate the corresponding vtu-files, which can then be loaded into ParaView.