Week 7: Shock tube simulation project
Aim:- Setup a transient shock tube simulation plot the pressure and temperature in the entire domain.
Introduction
Shock tube are the device which is used to study chemical kinetics. Shock tube consists of two chambers and a diaphargm which seperates the two chambers. One side is the high pressure gas other side is low pressure gas. Mixing occurs only when diaphargm is removed due to the pressure difference in the two chamber shock wave developed and reflected from the walls where compression and reflection occurs.
In a real life example of shock tube is auto-ignition system. Tube is filled with fuel and air in the two chamber due to molecular collision and shock wave temperature increases in the tube and auto-ignition occurs. Shock tube data can be used to see the ignition delay, so the shock tube data is very useful to compare the analytical and experimental data.
Geometry
Import the given geometry by drag option
Dimensions in shock tube
Shock wave tube is divided in to two region high and low pressure region, high pressure region represent green colour and low pressure region represent brown colour.
Case-setup
Application-Type: Time based
Materials- Reaction mechanism is used
Simulation parameter-
Simulation Time parameter
High pressure region
Pressure-6 bar
Temperature-300K
High pressure region field with nitrogen
Low pressure region
Pressure- 1.01325 bar
Temperature- 300K
Low pressure region field with oxygen
Boundary condition
High pressure - Boundary type-wall
slip condition
Low pressure region- Boundary type-wall
slip condition
Events
Events are used to connect or disconnect two regions at the desire instant of time. The higher pressure region kept closed till 0.001sec. At 0.001 sec regions are opened allowing the gases to interact , simulating the rupture of the diaphram.
RNG-k-epsilon turbulent model is used.
Grid size
Grid size of 1 mm is used.
Adaptive mesh refinement is used for nitrogen species, with sgs value of 0.001
Result
Mesh is generated as per the AMR Nitrogen Species cell count is varies with wrespect to time.
is
The diaphram is popped at 0.001s and it can be noted that the cell count remain constant upto that time. Once the diaphram is open the cell count varies and start to increases. This is because the mixing of nitrogen cause the concentration of nitrogen to reduce and thus cause refinement of the cell. When the wave reflect back the nitrogen return to high pressure region increasing the concentration of nitrogen, causing a reduction in the cell count, the cell count thus increases and reducing again when the shock waves move to and fro .
When the two region allow to interact at 0.001s nitrogen expands from high pressure region to the low pressure region and compressure wave can be seen in the low pressure region.
Variation of pressure in high and low pressure region can be saw from the plot
From the above plot we can seen that pressure in both the region is constant up to 0.001 sec there after pressure of high pressure region falls down and low pressure region increases due to intermixing of particles. For the generation of shock pressure is rapidly increases and decreases in both the region. Variation of pressure contour can be observed from the pressure animation.
Mean temperature of high and low pressure region can be seen below
From the above plot we can say that temperature of the low pressure region increases and high pressure region decreases due to compression in oxygen and expansion of nitrogen.
Conclusion
Variation of pressure temperature in the shock tube is simulated through the time 0.003 sec. The refinement of the mesh with the changining of nitrogen concentration is observed.