Shock tube simulation project

AIM:

• Setup a transient shock tube simulation
• Plot the pressure and temperature history in the entire domain - Explain the result
• Plot the cell count as a function of time - Explain the result

Shock Tube: The shock tube is an instrument used to replicate and direct blast waves at a sensor or a model in order to simulate actual explosions and their effects, usually on a smaller scale. Shock tubes (and related impulse facilities such as shock tunnels, expansion tubes, and expansion tunnels) can also be used to study aerodynamic flow under a wide range of temperatures and pressures that are difficult to obtain in other types of testing facilities. Shock tubes are also used to investigate compressible flow phenomena and gas-phase combustion reactions.

The following geometry represents the setup of high pressure (driver) and low pressure (driven). The separator (diaphragm) is suddenly burst, which initiates the flow from the high-pressure region to the lower one.

Case setup:

• High-Pressure zone - N2 (pressure 6e5 pascals)
• Low-pressure zone - O2 (pressure 1atm)
• Diaphragm surfaces has been deleted to avoid non-manifold error
• The mesh size is chosen to be 2.5mm with AMR for species N2 as a subgrid parameter with embedding level 0f 3 along with sub-grid-scale to be 0.001.

Results and Discussions:

Mesh aftershock

Observation:

• The effect of AMR can be seen clearly, Since no inlet and outlet the shock wave re-propagate inside the shock tube, which leads to unstable mesh refinement throughout, the high-pressure region is the dominant region for mesh refinement since the pressure needs to be stable from a higher value to mean value.

Total Cell counts:

Observation:

• The End-time for simulation was chosen to be 0.03 sec, which is the reason the total cell counts have been larger.
• The maximum cell count can be seen as around 13 000 cells.

Pressure and temperature simulations:

In the case setup process, Regions and Events enable the opening and closing of mixing separate regions. Here, after 0.001s the diaphragm has been opened and the variation can be observed through animation.

Pressure plot throughout the time domain:

Temperature plot throughout the time domain:

To conclude, both pressure and temperature from the high regions will take some time to reach mean values in the process.