[dydewangga]

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?

[ghorrocks]

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

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

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?

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

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

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.

[dydewangga]

Originally Posted by ghorrocks

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


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


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


must i using some CEL to define my boundary case?

[ghorrocks]

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.

[dydewangga]

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

[ghorrocks]

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

[dydewangga]

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

[ghorrocks]

Have you tried the CFX documentation?

[dydewangga]

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

[ghorrocks]

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

[dydewangga]

I'm not too understand at all ghorrock
can we define an expression like this mathematical function for the inlet


with Po=10MPa, and theta 1 ms to get this plot for the inlet


I hope you can help me

[ghorrocks]

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.

[dydewangga]

is that means i need to define mass flow rate as my inlet? I have the information for the mass flow rate


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


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

[ghorrocks]

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.