# blast simulation, blast wave, pressure wave simulation

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 March 22, 2015, 04:59 blast simulation, blast wave, pressure wave simulation #1 New Member   dewangga yudistira Join Date: Jul 2014 Posts: 8 Rep Power: 10 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?

March 22, 2015, 06:13
#2
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Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,367
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Quote:
 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.

Quote:
 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.

Quote:
 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.

April 7, 2015, 11:20
#3
New Member

dewangga yudistira
Join Date: Jul 2014
Posts: 8
Rep Power: 10
Quote:
 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?

 April 7, 2015, 21:23 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,367 Rep Power: 139 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.

 April 11, 2015, 02:52 #5 New Member   dewangga yudistira Join Date: Jul 2014 Posts: 8 Rep Power: 10 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

 April 12, 2015, 07:50 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,367 Rep Power: 139 I would recommend using a mass source point, not an inlet for this. Give that a try first.

 April 15, 2015, 22:15 #7 New Member   dewangga yudistira Join Date: Jul 2014 Posts: 8 Rep Power: 10 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

 April 16, 2015, 03:50 #8 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,367 Rep Power: 139 Have you tried the CFX documentation?

 April 16, 2015, 20:55 #9 New Member   dewangga yudistira Join Date: Jul 2014 Posts: 8 Rep Power: 10 I read some of tutorial, which one did you mean?

 April 17, 2015, 05:44 #10 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,367 Rep Power: 139 I do not think any tutorials use source points. The modelling guide and other documentation explains them well.

 April 25, 2015, 08:23 #11 New Member   dewangga yudistira Join Date: Jul 2014 Posts: 8 Rep Power: 10 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

 April 26, 2015, 19:33 #12 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,367 Rep Power: 139 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.

 April 26, 2015, 22:43 #13 New Member   dewangga yudistira Join Date: Jul 2014 Posts: 8 Rep Power: 10 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?

 April 27, 2015, 06:06 #14 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,367 Rep Power: 139 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.

 Tags blast, blastwave, cfx & fluent, define, function of time