Project

SHOCK TUBE SIMULATION

SHOCK TUBE SIMULATION

Introduction:

A shock tube is a device for studying shock waves. Prior to starting an experiment, a diaphragm inside the tube blocks any flow. You increase the pressure on one side, such as with a compressor, and then start the flow by rupturing the diaphragm. The gas expands down the other half of the tube.
Shock tubes 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.

Shock Waves:

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.
An object such as jet is said to have supersonic speed if it travels faster than the speed of sound. such speed is defined using mach number
In particular, shock waves travel faster than sound, and their speed increases as the amplitude is raised, but the intensity of a shock wave also decreases faster than that of a sound wave, because some of the energy of the shock wave is expended to heat the medium in which it travels.

Case Setup:

Shock tube sketch in converge CFD

Application: General flow

Materials:

Simulation parameters:

Boundary Conditions:

Regions & Initialization:

Events:

Base Grid:

Adaptive Mesh Refinement:

Simulation Results:

Surface with edge contour:

Pressure Contour & Plots:

Explanation:

By visualizing the contour we can say that there is high pressure region and the low pressure region which is separated by the diaphragm. The diaphragm block the flow from high pressure region to low pressure region.
At 1ms the the diaphragm is ruptured and the flow from the high pressure region expands, the expansion spreads in the form of rarefaction wave. And thus the pressure in the low pressure region is increased.
When the wave hits the wall it is reflected back, By that the low pressure region is expanded and compresses the high pressure region which inturn decreases the pressure in low pressure region.
While the wave travels back & forth, the shock wave is generated.

Temperature Contour & Plots:

Explanation:

Initially the temperatures are equal in both the regions, When the diaphragm is ruptured the flow in the high pressure region is expanded and compress the low pressure region, Which inturns increases the temperature in the low pressure region and decreases the temperature in the high pressure region
And the temperature in the low pressure region will be greater than the high pressure region because of the compression in the low pressure region.
By visualizing the plot we can see that there is a discontinuity in the temperature that is because when the two regions make contact there comes the discontinuity in the temperature, which is also called as cold front.

Velocity Contour & Plots:

Explanation:

Initially there is no velocity in both the regions, Once the diaphragm is ruptured the flow travels with the uniform velocity, Once the flow hits the wall the waves gets reflected and travels back & forth.
As a result the shock waves are generated after getting reflected.

Cell Count:

Explanation:

Initially the cell count is low, But after 1ms the diaphragm is broken the cell count tend to rise that is because we are using the species type adaptive mesh refinement.
We can see in the animation that N2 expands to the O2 region which inturn increases the cell count beacuse we are using the N2 species type AMR.
And also we can see there is a reduce in cell count after some period that is because of the reflected wave which is preventing the mixing process, As the result the cell count is reduced.
But it is flowing back & forth which inturn increases and decreasing the cell count according to the species concentration.

Conclusion:

The transient shock tube simulation is set using the converge CFD and the results are post-processed and explained.

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