Shock tube simulation project

SHOCK TUBE:

The shock tube is one of the simple laboratory apparatus that can generate various flow speeds at different flow regimes. The shock tube performance is based entirely upon the pressure ratio and speed of sound in the driver and driven section. The strength of shock increases in the ratio of the speed of sound. Considering a shock tube where the shock wave is generated by rupturing thin diaphragms instantly with appropriate pressure ratios across the driver and driven section of the shock tube. The pressure rises across the primary and reflected shock is measured by high-frequency pressure transducers located towards the end of the driven section. All necessary shock tube parameters are calculated through one- dimensional shock tube relations and are validated with experimental data.

2D-View of shock Tube

In this case, we are doing a compressed-gas driven method. By using the Events in the converge studio the diaphragm between the high-pressure zone and the low-pressure zone is opened at 0.01sec(1 millisecond). This creates compression waves that propagate into the driven section and Expansion waves which propagate to the driver section. Due to the high-pressure rations, these compression waves are converted into the shock waves in the driven section that rapidly accelerates the pressure and temperature in the Driven section on the other hand in the Driver section due to the expansion waves the pressure and temperature in the driver section are decreases. The thin layer that separates the two fluids will move forward into the Driven section. Due to the wall surface at the Driven section, the shock wave reflected back towards the Driver section creation resistance for the mixing of two fluids.

SHOCK TUBE APPLICATIONS:

• Shock Tube is an instrument used to replicate and direct blast waves at a sensor or a model in order to simulate actual explosions and their effects usually on a smaller scale.
• 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 used to investigate the compressible flow phenomenon 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.

SIMULATION:

• The transient solver is used for 0.03sec with a minimum time step of 1e-9sec.
• The pressure maintained at Driver and Driven sections is 6 bar and 1bar respectively and the 300K temperature is maintained at both the sections.
• N2 is used in the High-pressure region and O2 is maintained at the Low-pressure region.
• The adaptive mesh refinement technique is used based on N2 species with 0.01sgs.
• With the help of Events, the diaphragm between the regions is opened at 0.01sec.

The model used for doing the simulation.

The cell count is rapidly changing because we are using the Adaptive mesh refinement on the basis of the N2 species after opening the Diaphragm the shock wave is produced which gives the sudden acceleration in the medium that makes the N2 species disperse into the low-pressure region this makes the mesh finer when the N2 species diffuses into the low-pressure medium. This process will repeats until the uniform pressure is obtained in the shock-tube.

The mean temperature and pressure plots in High-pressure regions:

The mean temperature and pressure plots in Low-pressure regions:

• On observing the temperature and pressure plots of both regions we can see that the shape of the graph is repeating itself with reduced amplitude with respective time. This is because every time you see the increase in temperature and pressure in the plot at that time the shock wave is traveling in that region.
• The shock wave carries energy with a high enthalpy when the wave passes in the medium it increases the energy in the medium in the form of temperature and pressure. Whenever shock wave passes through the medium the entropy of the wave increases this is one of the main reasons for the decrease in the amplitude of the wave.
• The diving force of the shock wave is pressure difference whenever the pressure difference id reduced the amplitude of the waves in the plot also decreases

The below videos will support the theory which we are discussed.

The pressure, velocity, N2 species contour Video Link: https://youtu.be/bUZ2dXoGAJ8

The Temperature Contour video Link: https://youtu.be/AyC-jCS5n-0

From the above video, we can notice that the reflected shock wave will create some resistance for mixing the two fluids.

The energy of the shock wave decreases with respective time this can be observed by seeing both pressures and velocity contours.

When the shock wave hits the wall surface where the temperature for the medium rapidly increases remain it for some time.