Shock tube simulation

Objective:

To setting up the Shock tube simulation problem using Converge Studio .

• Setup a transient shock tube simulation.
• Plot the pressure and temperature history in the entire domain.
• Plot the cell count as a function of time.

SHOCK TUBE:

The 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 (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 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. 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 buildup of high pressures which cause diaphragm(s) to burst and a shock wave to propagate down the shock tube (compressed-gas driven).

Application:

• Shock tubes have been used to measure dissociation energies and molecular relaxation rates.
• The fluid flow in the driven gas can be used much as a wind tunnel, allowing higher temperatures and pressures therein replicating conditions in the turbine sections of jet engines.
• They have been further developed into shock tunnels, with an added nozzle and dump tank. The resultant high temperature hypersonix flow can be used to simulate atmospheric re-entry of spacecraft or hypersonic craft, again with limited testing times.

GEOMETRY SETUP:

• Importing STL file to Converge CFD Studio.
• We saw that diaphragm between the two different region , so we need to delete the surface.

Boundary flagging:

• From the above Boundary flagiing shows that its having two regions such as High pressure Region & Low pressure Region.
• According to that High pressure & Low Pressure 2D front and 2D back will be marked.

Diagnosis:

• Checking the diagnosis method like normal and Nonmanifold problem.

Boundary region by group:

case setup:

Material setup:

Gas simulation:

Global Transport parameters:

Reaction Mechanism:

Simulation parameters:

Run parameters:

• Solver : Transient method with Full hydrodynamic

Simulation time parameters:

• In this method used to setting up the start time and end time of simulation with initial time step and minimum time step

Solver parameters:

Boundary condition:

High pressure Boundary condition:

• High pressure Region should be marked with : Wall using slip condition

High pressure boundary condition with 2d front and back.

Lower pressure Boundary condition :

• Lower pressure Region should be marked with : Wall using slip condition

Lower pressure boundary condition with 2d front and back.

Initial conditions and Events:

Regions and initialization:

• Creating High pressure regions with following data

Temperature(K)- 300 K.

Pressure(pa) - 600000.0 pa.

with species N2 - 1 Mass Fraction.

• Creating Lower pressure regions with following data

Temperature(K)- 300 K.

Pressure(pa) - 101325.0 pa.

with species O2 - 1 Mass Fraction.

Events:

• Events are used to used to connect and disconnect two regions for the instant of time.
• Simulating the shock tube its used to diaphragm are mixed region.
• From the above the Sequential methods are used to setup the region , to regions High_pressure and Lower_pressure are closed till 0.001s.
• After that both regions are open after 0.001s and its mixing the regions.

Physical Model:

Turbulence modeling:

model:RNG K-Epsilon

Grid Control:

Base Grid:

Adaptive mesh Refinement:

In adaptive mesh refinement (AMR) is a method of adapting the accuracy of a solution within certain sensitive or turbulent regions of simulation, dynamically and during the time the solution is being calculated.

• Used to refinement the cell according to simulating.
• Maximum cell :200000
• Selecting the Active regions : High_pressure, Low_pressure.
• Selecting the Species:N2 with permanent,SGS:0.001.

output/post processing:

Post variable selection:

Output files:

Simulation Running:

• We need to Export the Export inputs files to floder.
• After setting up the case full we need to run the simulation.

Cygwin:

• Cygwin is used to run the simulation.

cygwin/pwd/cd converge_runs/cd support_cases/cd st.

output:

Mesh grid size: 1mm

Surface with Edges:

AMR:

Animation:

Pressure contour:

Animation:

Velocity contour:

Animation:

Temperature contour:

Animation:

Temperature plot:

Presssure plot:

Cell count:

Total cell count

• Maximum cell count observed that nearly 9000 cells.

cell count using processor running:

Conclusion:

• The above result shows that simulation of the shock tube is done.
• With help of Event method we simulate shock tube at particular time two regions mixed according to the pressure.
• With help of uses of an adaptive mesh refinement method with respect to species such as O2 & N2, its clearly show that when increases in density of certain region its also changes in the Adaptive mesh refinement is required to changes according to the flow through the regions.
• Maximum cell count reaches 9000 due to AMR ,Initially 2000 cell there is no change to due Event method after that diaphragm break fluid mixing of two regions takes place.
• When its reachs certain time step high pressure regions mixed with lower pressure region with this method low pressure regions change its pressure and velocity according to reaction of the two species of N2 with o2.