Modeling blast wave FSI, avoiding reflectivity and divergence

KeganLeckness · August 13, 2015, 15:56

Hi,

I'm in need of some advice in a two-way FSI simulation using Fluent/Mechanical. I'm modeling blast wave propagation through the ear and am having difficulty applying the pressure in such a way I get the waveforms I need.

See Fig_1. My model consists of three domains. Domain A and C are fluid (air) domains separated by a membrane, domain B. I'm interested in the pressures at the entrance of domain A and on either side of domain B.

The difficulty is here:
The triangular pressure waveform representing the oncoming blast wave can be seen in Fig_2. Assigning this pressure as a UDF on the entrance of domain A does not work - a reflecting wall is put up by Fluent to resist flow coming out of the 'pressure-inlet' and the pressure wavefront continually bounces back and forth between the entrance of domain A and the membrane, B. Implimenting the option to turn off the reflecting, artificial wall changes the waveform too much to be applicable to my case - it destroys the impulse nature of my triangular waveform.

I then tried adding an external flow field to the entrance of domain A, as seen in Fig_3, with a small pressure-inlet. All other boundaries of the external flow field were set to 0 Pa pressure-outlets. Doing this limited the reflectivity issue significantly.

Now, if I apply a 70 kPa pressure to the inlet of the external flow field, only 20 kPa is passed into domain A. Applying greater pressures (>100 kPa) to the external flow field yields AMG temperature Divergence.

Adding the additional domain got rid of my problem of reflectivity, but has limited the pressure levels I can reach inside domain A.

I'm more of a CFX guy (switched for dynamic remeshing) and need asssitance in working around this.

Any advice would be appreciated.
Thank you,
Kegan Leckness
Fig_1.PNG

Fig_2.PNG

Fig_3.jpg

Note: the imaged model is conceptual; mesh quality of the real model is a non-issue.

August 13, 2015, 15:56	Modeling blast wave FSI, avoiding reflectivity and divergence	#1
KeganLeckness Member Kegan Leckness Join Date: Mar 2015 Posts: 38 Rep Power: 11	Hi, I'm in need of some advice in a two-way FSI simulation using Fluent/Mechanical. I'm modeling blast wave propagation through the ear and am having difficulty applying the pressure in such a way I get the waveforms I need. See Fig_1. My model consists of three domains. Domain A and C are fluid (air) domains separated by a membrane, domain B. I'm interested in the pressures at the entrance of domain A and on either side of domain B. The difficulty is here: The triangular pressure waveform representing the oncoming blast wave can be seen in Fig_2. Assigning this pressure as a UDF on the entrance of domain A does not work - a reflecting wall is put up by Fluent to resist flow coming out of the 'pressure-inlet' and the pressure wavefront continually bounces back and forth between the entrance of domain A and the membrane, B. Implimenting the option to turn off the reflecting, artificial wall changes the waveform too much to be applicable to my case - it destroys the impulse nature of my triangular waveform. I then tried adding an external flow field to the entrance of domain A, as seen in Fig_3, with a small pressure-inlet. All other boundaries of the external flow field were set to 0 Pa pressure-outlets. Doing this limited the reflectivity issue significantly. Now, if I apply a 70 kPa pressure to the inlet of the external flow field, only 20 kPa is passed into domain A. Applying greater pressures (>100 kPa) to the external flow field yields AMG temperature Divergence. Adding the additional domain got rid of my problem of reflectivity, but has limited the pressure levels I can reach inside domain A. I'm more of a CFX guy (switched for dynamic remeshing) and need asssitance in working around this. Any advice would be appreciated. Thank you, Kegan Leckness Fig_1.PNG Fig_2.PNG Fig_3.jpg Note: the imaged model is conceptual; mesh quality of the real model is a non-issue.