Importance of Shock Tube simulation by CONVERGE CFD

Title: Importance of Shock Tube simulation by CONVERGE CFD

Objective: 1. To Understand importance of Shock Tube

                2. Setup for Shock Tube in CONVERGE Studio 

                3. Observe the effect of shock on Pressure ,Velocity & Temp.

What is Shock Tube?

              Shock tube its used for observe the chemcal kinetics .its a parallel tube in which there is two region first high pressure & second low pressure. in between two region there is diphragram is provided. when diphragram is broken high pressure zone is impact on low pressure zone. so, there is create shock & due to the shock there is sudden change in Pressure, Temprature & velocity.

Application of Shock Tube

            its used for determine the ignition delay period. on one side there is provide the fuel i.e high pressure region & on other side is air which is in low pressure zone. so, when there is interface is broken there air & fuel mixture is start to burn due to high press & temp. so, here we can find out ignition delay period.

CASE SETUP

1. Application type> Time based

2. Material>air 

3. Simulation time parameter

• solver> Transient , Simulation mode> Full hydrodynamic 
• Start time>0 sec , end time>0.003sec
• Initial & minimum time step=1e-9
• Maximum time step=1
• Navier stroke solver> Density based

4. Boundry name & type

As we want to capture the 3D flow . Boundry type is wall & velocity Boundry conidtion is Slip. there is no any 2D boundry

Region & Initilization 

As shock Tube is divided in to two region high pressure (N2)&Low Pressure (O2)

For high Pressure 6bar pressure is provided.

Low Pressure

Low pressre side is provided 1bar static press.

Event

Event it is used for separate the two region by disconnected triangle having no boundry condition in between them. 

• when there is no any from high press to low press diphragram is CLOSE
• when there is flow from high press to low press diphragram is OPEN at 0.001 sec

• Turbulent model= K-epsilon model
• Base grid size=0.002m

Adaptive Mesh Refinment

Adaptive mesh refinement is provided for capture the flow correctly. its one type of moving Mesh provided. So, as N2 species move according to that mesh is move & mesh is get refined

Output file

Mesh 

 Adaptive Mesh Refinement(AMR)

On the middel side we can see that AMR is it move or refined according to the movement of N2 species

Pressure contour

From below contour we can see that, as flow is flowing from high pressure to low pressure. there is on righ side high press. is created 

Temprature Contour

so, from below contour we can see that as high press. fluid is mix with low pressure there is suddenly temprature increasse & decrease throughout the tube. so, on right side we can see that there is high temp is occur 

Velocity contour

as flow fluid is flowing from high press to low press. there is velocity is continously is change 

1. Mean Temp 

as the initial condition is provided 300k for both low & high pressure zone. As suddenly high press (N2) is strike on to the low press (O2) . on low press side is temp. is higher & on high press. side is low temp. is developed

2.Pressure 

 From below plot we can see that, on high press. side initial pressure is 6 bar , while on low pressure side is 1 bar . when high press is interact with low press. foloowing profile is created

3.Total cell 

From total cell count we can see that from 0-0.001 sec Diphragram is CLOSE, Once 0.001 sec is over the Diphragaram is broken & there is Adaptive mesh Refinement is active (AMR), So, we can that suddenly there is cell count is increase & it proceed as high press (N2) is interact with Low press. (02). 

Base mesh grid size is provided is 0.002m

Pressure animation

Velocity animation

 Overall conclusion 

1. Shock tube experiement is help for find out the chemical kinetics like we can find out the ignition delay period in internal combustion engine.

2.As high press. zone is combine with the low press. zone its observed that suddenly rise in Pressure & Temprature on low press. zone

3.Adaptive mesh refinment is applied. so, mesh is refined on the basis of N2 species. which help for capture the good result.