Shock tube simulation project using Converge CFD

Procedures:

1. Preparing a channel to stimulate simple flow using Converge CFD.
2. Setting up the boundary conditions & simulation setup.
3. Base Grid meshing is to be
   • dx = dy = dz = 0.001m
4. Grid Control with the following Adaptive Mesh species Sub-Grid Scale conditions,
   • SGS=0.001
5. Using CYGWIN to execute the CFD solver.
6. Use Converge CFD to post convert the output files to ParaView format.
7. Paraview to Post Processing the results.

Inputs:

• Inlet Pressure = ( Based on Initial Conditions )
• Channel Length L = 0.2 m
• Channel Width, Height = 0.01 x 0.01 mts
• Fluid Medium = Gas (Nitrogen & Oxygen)
• Total Simulation Time= 0.003 Sec
• Solver Type = Transient
• Pressure of Nitrogen Region = 600000 Pa
• Pressure of Oxygen Region = 101325 Pa

Project Overview:

The idea behind this project is to simulate the transient gas flow in a shock tube and study the sudden variations in pressure, velocity, temperature during the gasses collision as one gas having higher pressure whereas the other having lower pressure.

Pre-Processing & Setting up Boundry Conditions:

Setting up Regions Condition:

In this simulation, we had created two regions. Region 0 having the N2 gas under high pressure & Region 1 having O2 gas under low pressure. Boundaries are flagged with respect to their boundaries.

Mesh Grid:- 0.001

Grid with Adaptive Mesh Refinement:

In this Simulation, Adaptive Mesh Refinement is used under grid control for capturing the shock wave with fine mesh to provide us accurate results. The Sub-Grid Scale is set to 0.001m with maximum embedding level up to 3.

Pressure with respect to Time:

When the wall between the regions got removed shock waves are produced as the high-pressure gas flows to the low-pressure region. The initial rise in pressure is due to the N2 gas which pushes the oxygen gas to some extent then the oxygen gas pushes backs the nitrogen gas which results in decrease in pressure as we can see that from the plot representing a rise followed by fall and repeating these progress until the gases attain stable pressure.

Temperature with respect to Time:

Maximum Temperature occurred during simulation:

Minimum Temperature occurred during simulation:

Mean Temperature occurred during simulation:

Velocity with respect to Time:

Total cells allocated with respect to Time:

The above figure shows that the solver took 2000 cells to solve the stationary gases in the medium. After the wall between the regions got removed by 'Sequential Events Condition' the reaction takes place as high-pressure gas flows to the low-pressure area which generates shock. This is the reason that the solver took higher number of cells to capture the shock over the adaptive mesh region cells.

Processor's Ranked Cells allocated with respect to Time:

Post Processing Output Files:

Species Mix Contours:

At the initial simulation, the highly pressurized gas (N2) tries to compress the low pressurized gas (O2) which at some extend the low-pressure gas is pressurized and pushes back the nitrogen gas to and fro & then these gases mix up with each other resulting in a stable condition. This could be reviewed further on pressure variation contour & temperature variation contour animation clips for sudden shock occurrence in the system.

Pressure Variation Contours:

Temperature Variation Contours:

Simulation Run Log Details:

• Total Cell Count is 7033.
• Total time taken by the solver to complete this simulation is found to be 81 sec.
• From the velocity & temperature plots, we can see that the oscillating wave decreases with an increase in time. This shows that the gases inside the shock tube will come to stationary condition after some time.