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 Stephen McIlwain November 23, 1998 07:27

Blast Waves

Hi, I've found many answers to some of my own personal CFD questions on this site - I hope someone can help me with this specific problem. I'm trying to model the effects of a blast wave emanating from ignition of a solid rocket motor. This would naturally include pressure information as well as information on the decay of the pulse. I tried to model this quickly using commercial CFD (in unsteady mode) with a lot of problems and not much success. Somebody mentioned the use of a hydrocode for this type of calculation and I have contacted one or two vendors. My question is what is the essential difference between standard CFD codes and these hydrocodes, why are they recommended particularly for blast or moving shock waves and has anybody modelled a similiar problem to mine? Any help appreciated.

 John C. Chien November 23, 1998 10:52

Re: Blast Waves

Launch ignition transient problem is a very specialized field , which has been studied by using 1-D, 2-D, 3-D inviscid, and 3-D viscous approaches. The best place to start is AIAA journal and AIAA papers.

 Dan Williams November 26, 1998 22:29

Re: Blast Waves

Howdy,

None of the current crop of popular commercial CFD codes can do a decent job at something like this. Basically it's pointless in trying. Most of them are inherently based in technologies used for subsonic flow, which limits them when it comes to high speed flow. Some of the codes can do steady calculations of transonic to slightly supersonic flows, but pretty much all of them do a crappy job at any high speed transient flow with shocks, contact discontinuities and so on.

This is not a weakness, it's just the way it is. Most flows of "engineering" interest are not transient supersonic compressible flows anyways.

"Hydrocodes" is a synonym for codes that are specifically designed for transient compressible flow. One problem with "hydrocodes" as they are sometimes termed is that many of them are classified. Used only by military and government agencies. Which is stupid, since the technologies they use are in the public domain.

The only commerical code I'm aware of that is capable of accurately handling these problems is put out by Combustion Dynamics from Medicine Hat, in Alberta, Canada. They have a website:

http://www.combdyn.com/

Not too much info there, but if you contacted them I'm sure they would help you out.

Dan W.

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