Week 7: Shock tube simulation project

Aim: To perform a shock tube simulation

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 in detail

It is expected to show the mesh generation in the form of Paraview

Also create animation and upload it

Theory Explanation:

The shock tube is an instrument used to replicate and direct blast waves at a sensor or a model in order to simulate actual explosion and their effects , usually on the smaller scale shock tubes, ( and 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 temp and pressure that are difficult to obtain in other testing facilities , shock tubes are also used to investigate compressible flow phenomena and gas phase combustion reactions. More recently , shock tubes have been used in biomedical research to study how biological specimens are affected by blast waves.

A shock wave inside a shock tube may be generated by a small explosion ( blast-driven) or by the build up of high pressure which cause diaphragm (s) to burst and a shock wave to propagate down the shock tube( compressed gas driven).

In General there are two types of shock tubes:

Both compression-driven and blast-driven shock tubes are currently used for scientific and military applications.

Compressed -gas driven shock tubes are most easily obtained and maintained in laboratory conditions, however the shape of the pressure wave is different from blast wave in some important respects and may not be suitable for some applications.

Blast-driven shock tubes generate pressure waves that are more realistic to free -field blast waves , However the require facilities and expert personnel for handling high expensive.

Working:

A simple shock tube is a tube, rectangular or circular in cross section , usually constructed of metal , in which a gas at low pressure and a gas at high pressure are separated using some form of diaphragm through the low pressure section. The shock that eventually forms increases the temperature and pressure of the test gas and induces a flow in the direction of the shock wave. Observations can be made in the flow behind the incident front or take advantage of the longer testing times and vastly enhanced pressure and temperature behind the reflected wave.

The low-pressure gas, referred to as the driven gas , is subjected to shock wave , The high pressure gas is known as driver gas. The corresponding sections of the tube are likewise called the driver and driven sections. The driver gas is usually chosen to have a low molecular weight. ( e,g helium or hydrogen) for safety reasons , with speed of sound ,but may be slightly diluted to tailor - interface conditions across the shock . to obtain the strongest shock the pressure of the driven gas is well below the atmosphere pressure ( a partial vacuum is induced in the driven section before detonation).

The bursting diaphragm produces a series of pressure waves, each increasing the speed of sound behind them , so that they compress into shock propagation through the driven gas, This shock wave increases the temperature and pressure of the driven gas and induced a flow in the direction of the shock wave but at lower viscosity that the lead wave simultaneously , a refraction wave , often referred to as the prandtl -Meyer wave travels back in to the driver gas.

Applications:

Biomedical research like inserting of medicine, Military applications like missile launching, Mining purpose, Blockage removal in the sewage plant.

Simulation Setup:

1. Converge Studio: To pre - process the data that needs to simulate the caste, it plays an important role in generating important 3D inputs files only using GUI . It does not run simulation directly , However it generates inputs files which use to run the simulation.
2. Cygwin: Cygwin is a collection of GNU and open -source tool that provides functionally similar to Linux distribution on Windows.
3. Paraview: To post_processing to obtain the contour plots, etc.,, It is an open source multi -platform data analysis and visualization software.

Geometry Setup:

Case Setup/ Simulation setup:

Material:

Gas Simulation:

* Air is used as working medium hence un check the reaction mechanism.

* Predefined Mixture: Air

* Enable species: ( not In mech.data) as we want to assign the participating species of air like O2 and N2.

Global Transport Properties:

Global transport Parameters:

Species:

Simulation parameters:

Run Parameters:

Simulation time Parameters:

Solver Parameters:

Boundary Condition:

For all the boundary conditions High pressure, Hp_2d_1,Hp_2d_2,Low pressure, Lp_2d_1,Lp_2d_2, where the boundary type as Wall and velocity B.C is slip .(as the shock expansion waves are getting reflected from the boundaries).

Initial conditions:

Select Events also in case setup,because of merging the regions

Regions and Initialization:

There are two regions in this simulation

1. High Pressure Region

2.Low Pressure Region

High Pressure Region:

Low pressure Region:

Events:

Turbulence Model:

Grid Size:

Adaptive Mesh Refinement:

Post Variable selection:

Output Files:

Export Files:

The data files are exported from converge to run the simulation

And then By using CYGWIN parallel processor the simulation is performed.

post Converting:

Now we need to convert all the output files which are processed by converge MSMPI into the files which will be readable for post processing the results in Paraview.

Paraview:

In Paraview we can see the results of contour plots of the flow parameters.

Results:

Pressure Plots for high and low pressure regions:

There is no Pressure Disturbance upto 0.0012 ,after that the pressure is fluctuating from low_pressure region to High_Pressure region due to the slip condition.

Temperature plots for high and low pressure regions:

There is no pressure difference upto 0.0012 seconds, after that heat transfer takes place vice versa from high pressure region to low pressure region due to slip boundary condition.

Mesh: with a size-0.002 M

Pressure contour:

Temperature contour:

Animation:

Pressure:

https://drive.google.com/file/d/1U5-QWRBEiHa46q_4u_DXLeUVdkH4s8Nl/view?usp=sharing

Temperature:

https://drive.google.com/file/d/1MY77tadqV0AO_-Hw1olonSCl_b8KI5gs/view?usp=sharing

Conclusion:

*As we have observed the pressure at High Pressure region Exceeds maximum diaphragm pressure the diaphragm gets ruptured and due to this , there is a pressure difference created.

*The High pressure regions tend to move towards the low-pressure region which lead to formation of shock waves in that region which increases sudden Pressure and Temperature on that low pressure region .

*On the other side , in the High-pressure region, the expansion wave will be created due to the pressure relaxation , where the Pressure and temperature decreases.

*Both the shock and expansion waves are interacting with each other after reflecting from the wall due to the slip Boundary condition.