Week 7: Shock tube simulation project
Shock Tube
It is an instrument which is 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 other 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.A shock wave inside a shock tube may be generated by a small explosion or by the buildup of high pressures which cause diaphragm to burst and a shock wave to propagate down the shock tube.
Aim
To simulate Shock tube simulation.
Geometry
Above is the geometry that is for the simulation.
Case Setup
Simulation- Transient
Boundary Conditions
High Pressure Region and Front 2D and Back 2D
Boundary Type- Wall.
Velocity BC- Wall Motion Type- Stationary, Surface Movement -Fixed.
Temperature BC- Zero Normal Gradient.
Low Pressure Region, Front 2D and Back 2D
Boundary Type- Wall.
Velocity BC- Wall Motion Type- Stationary, Surface Movement -Fixed.
Temperature BC- Zero Normal Gradient.
Regions and Events
High Pressure Region
Temperature- 300 K
Pressure- 600000 Pa
Species- N2
Low Pressure Region
Temperature- 300 K
Pressure- 101325 Pa
Species- O2
Events
The following is in set in Sequential Tab
| Start seconds | Event By | Region A | Region B | Event |
| 0 | Region | High Pressure | Low Pressure | Close |
| 0.001 | Region | High Pressure | Low Pressure | Open |
Turbulence Model- RNG k-`epsilon`
AMR- Species Tab
Name- N2
Timing Type - Permant
SGS Embed - 0.001
Mesh
Above is the mesh image in paraview where the grid size is given as 0.004 m.
Cell Count
This is the Cell count plot with respect to time. As you can see that the cell count varies from time to time starting at 0.001 seconds and continous till the end of the simulation time.This happens because of the event peroid set at 0.001 seconds.
Pressure Contours and Plots
Above are the pressure contour and plot, we can see that the pressure maintaied at a constant 0.35 MPa once the event began the pressure begins to drop becauce the diaphragm separatig the two regions i.e the High pressure region and the Low pressure region breaks down and the high pressure N2 moves to the low pressure region causing the reduction in pressure. Since the gases are in a closed section there is a little bit spike in the pressure due to the gases hit at the end of the segment and as the simulation progress the pressure beins to drop in significant amount. The movement of the gases can b viewed in the animation below.
Animation
Temperature Contour and Plot
Above the are the temperature contour and the plots, similar to the pressure there is a temperature change once the event began. As you can see that temperature is maintained at a constant of 300K which is set at region setup. Once the diaphragm ruptures there was a decrease in temperature of 230 K and when the gases travel further from the intial point there is an increase in temperature 350K and at the end of the shock tube temperature was 496K this is beacuse the gases where concentrated at a single point and the gas travels backwards. This event keeps on occurring till the end of the simulation but the temperature keeps on decreasing. This can be viewed in the animation below.
Animation
Conclusion
From this simulation we can see the factors which are affected by the shock waves and its behavior during these type of simulations.