Shock tube simulation project
Shock tube simulation project
OBJECTIVE:
- 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 DESCRIPTION:
- The shock tube is divided into two regions namely low and high-pressure region.
- When the diaphragm is broken and since there is no interface between the fluid in the high-pressure zone so fluid is directly going to enter the low-pressure zone.
- In addition to measurements of rates of chemical kinetics shock tubes have been used to measure dissociation energies and molecular relaxation rates they have been used in aerodynamic tests
- Because of this pressure difference, the shock waves develop quickly. Then the fuel and air mixture since shock waves occur and then auto ignition happens.
- From the shock tube data, the fuel and air mixture takes some minimal time to start ignition. This is known as ignition delay.
GEOMETRY AND BOUNDARY FLAGGING:
- The dimensions of the shock tube are given as shown in the figure: dx = 0.2m; dy = 0.01m; dz=0.01m.
- After that, we have to do a diagnosis for checking errors in geometry. In this geometry, it shows nanmanifold problems for this issue I have deleted an extra triangle to reduce the error.
- We are having two regions: High Pressure - Green colour; Low Pressure - Brown colour.
- This is a wall type of flow.
- We are setting up the flow problem in Two Dimensions.
BOUNDARY CONDITIONS:
- Application: General Flow; Predefined Mixture: Air
- Solver: Transient;
- Start Time: 0 s, End Time: 0.003 s
- Initial Time Step: 1e-9 s; Minimum Time Step: 1e-9 s; Maximum Time Step: 1 s
- High Pressure and Low Pressure: Law of Wall
- Temperature Boundary Condition: Law of Wall; Air @ 300K
- Pressure @ N2 Region: 1 bar; Pressure @ O2 Region: 101325 Pa and Temperature: 300k
- Turbulence Model: RNG k-ɛ
- Base Grid: 1mm;
- AMR: Permanent at 1mm for N2 with Max Embed Level 3.
- Events start from zero.
OBSERVATIONS:
Fig 1. Mesh(surface with edges)
Mesh Animation
VELOCITY CONTOUR:
Fig 2. Velocity mesh profile
Video 1. Velocity mesh animation
Video 2. Velocity animation
Pressure:
Fig 2. Pressure mesh profile
Video 3. Pressure mesh animation
Video 4. Pressure animation
TEMPERATURE CONTOUR:
Fig 2. temperature profile
Video 5. Temperature mesh animation
Video 6. Temperature animation
YN2 CONTOUR:
Fig 4. YN2 profile
Video 7. YN2 mesh animation
Video 8. YN2 animation
GRAPH PLOTS:
Fig 1. Mean Temperature
Fig 2. Max Temperature
Fig 3. Min Temperature
Fig 4. Max Pressure
Fig 5. Min Pressure
Fig 6. Pressure
Fig 7. Total cells and ranks
Fig 8. Total cell and regions
Conclusion:
The Velocity contour of the Shock Tube when viewed using ParaVIEW, the highest Velocity of air was reported to be 1.2e^-38. The highest Temperature inside the Tube was found to be 300k and the lowest was 170k.
When you observe the video above its clear that when diaphragm ruptures expansion and compression take place in the HP region and LP region respectively at the intial stage. Then the shock waves get reflected back from the boundary resulting in compression and expansion in HP region and LP region respectively for pressure animation. In the high-pressure region, we have N2 species and in the low-pressure region, we have O2 species which are at 1 bar and ambient pressure respectively. The contents of the species remain the same until 0.001 s where the flow transfer happens causing shocks to propagate. The simulation runs for only 0.003s and therefore if we allow the simulation to run any further it will reach the steady state value as the concentration decreases periodically.
From the cell count plot we can see that until 0.001 s the cell count is stable at 200 cells, once the diaphragm breaks we see that adaptive mesh refinement happens causing the fluctuations to happens in cell count and thereafter the cell count increases linearly before it falls down, this goes until the end time where cell count comes till 1200 cells.