blast simulation, blast wave, pressure wave simulation
 

hello

I'm trying to make blast simulation, in this case deflaragation / pressure wave blast of hidrocarbon (I used C1 as the fluid)

the simulation will be used transient function, is it better use cfx or the transient?

for the inlet boundary i will use sphere with pressure based on some function, can I input the function in ansys cfx?

i want to use 450 m/s with overpressure function of blast 0.35 bar and temperature 279 C , can I input it in the inlet of ansys cfx?

and i still dont understand, must i use outlet boundary condition with 0 m/s velocity or using an opening as my outflow?

Yes. Have a look at 1D interpolation functions, or CEL expressions.

Look in the CFX documentation for the available options for supersonic inlets.

You can use any boundary condition you like. As I do not know what you are modelling I cannot assess how suitable the options you list are.

But you cannot define an outlet with 0m/s velocity - then no flow will occur.

If this blast is to occur in a far field then an opening with zero relative pressure makes sense.

thank you ghorrocks
I'm already finished for the model, Im using point of blast as a sphere model
http://i.imgur.com/A8pjz3V.png
http://imgur.com/QwsCj3e.png
to make it supersonic I must used fluid whose density is a function of pressure, like CH4 or some gas phase hidrocarbon and set the fluid models>heat transfer as total energy right?

for the outlet I still confuse, must I used outlet or opening for boundary condition, for a distance I want to make the pressure and velocity normal
http://i.imgur.com/1vbX8K6.png

the blast simulation i want to make start from ignite point of blast ( i modelled as sphere) with 450 m/s (supesonic) 1.33 bar pressure and then for some radius the pressure and velocity will be normal
http://imgur.com/F6VF870.png

must i using some CEL to define my boundary case?

Your domain looks like minecraft. My kids like blowing things up in minecraft as well :)

Yes, for a compressible flow you need to use total energy as the heat transfer model.

An alternative to the outlet you can looking at is you can also do this using a source point. This is probably a better way of doing it if you want the explosion to start at a small point.

for the first i want to simulate simple model, if it works i will make it more complicated :)

I have some reference to do my simulation, but I still didnt understand how to input the parameter, can you help me to understand it ghorrocks? is it neccessary to using CEL to define the parameter?

link
http://journals.ajaums.ac.ir/files/s...-8-252065f.pdf

the simulation using transient analysis, but i dont get it how to generate blast shock wave from the inlet, please help me ghorrocks:)

I would recommend using a mass source point, not an inlet for this. Give that a try first.

thanks for answer my question ghorrocks

mass source? can you give me more explanation or example?

I still not understand how to set mass source for the inlet

Have you tried the CFX documentation?

I read some of tutorial, which one did you mean?

I do not think any tutorials use source points. The modelling guide and other documentation explains them well.

I'm not too understand at all ghorrock
can we define an expression like this mathematical function for the inlet
http://imgur.com/fw34ysE.png

with Po=10MPa, and theta 1 ms to get this plot for the inlet
http://i.imgur.com/5Xbczy0.png

I hope you can help me

The mass source approach requires a mass flow rate to be defined. Your function defines a pressure function. So that function is easy to implement at an inlet, but will require transformation to a mass flow rate if you want to use the mass source point approach.

is that means i need to define mass flow rate as my inlet? I have the information for the mass flow rate
http://i.imgur.com/GNVUejw.png

I also want to define the changes of pressure of blast from time
the pressure function that i show you in my last reply will give this kind of result, I read it from dissertation publication
http://i.imgur.com/xoYG5cv.png

i wonder how can he define the inlet to make this kind of simulation in cfx
any suggestion?

You cannot prescribe BOTH pressure and flow. To do so is a badly posed boundary condition. You can only prescribe one, and then you check the other is what you expect as a check things are working properly.