Shock tube simulation project

OBJECTIVE:

To set up a transient shock simulation and track the temperature and pressure history over time.

GEOMETRY AND BCS:

The geometry is divided into two regions. One region is filled with N2 at 6 bar pressure and the other region consists of oxygen at 1 bar pressure.

The two regions are separated by an imaginary diaphragm initially.

The diaphragm opens and the high pressure N2 gushes to the other side producing shock waves in the process which increases the temperature and pressure substantially.

RESULTS:

Mesh:

An adaptive mesh refinement is used to capture the shock waves and drastic temperature and presusure variations.The mesh for a certain time step is shown below.

As evident the mesh becomes finer in areas where shock wave is propagating.

Temperature History:

As it can be observed the temperature before 0.001 secs is constant. But after the diaphragm opens at 0.001 seconds the temperature stars changing rapidly.

The oscillations in the temperature can be attributed to the shock waves propagating in the tube.

Pressure History:

Similarly the pressure variation can be seen after the opening of the diaphragm.

The oscillating nature of pressure can also be attributed to the shock waves. These oscillations represent a dampening system and the variations die down over time .

Hence after the equilibrium state is reached the pressure and temperature reach a steady state value.

Cell count history:

The above graph shows the cell count history with time.

After the diaphragm opens at 0.001 secs a sharp rise can be seen in the cell count.

This is due to the AMR that refines the mesh whenever it senses a shock wave being generated and correspondingly increases the cells to capture the sudden fluctuations in quantities. Towards approaching steady state the cell counts again come down.