Sonic Choke? Maybe not. 2162 FPS

[Michael Loar]

I hate that I could not make the fun shoot but would love to see the " super " gun blowing the sun screens off the chrony and the ensuing exhilaration of all involved at the time.

You know what they say " No pictures means it did not happen " LOL.

Mike

[MJP]

Bob wanted this in here, along with the info.
Gun is AF style inline valve with 12mm porting to stem and 9.5mm stem port.
Barrel 540mm 357 16:1
250bar helium
Sabot around 1gram I'll weight that if I find one from my shop.
500cc tank
Ambient temp around 20C



Marko

[lloyd-ss]

Marko, 
Excellent work!  I had to get the calculator out to see just how fast that is in fps:  2,787fps !!!
And you are thinking about 15 grains for the projectile?  The inline valve and the helium really make a big difference when going after maximum velocities.
Very good!
Lloyd

[MJP]

Thanks Lloyd, it does work wonders on helium. I'll update the weight of the projectile if and when I find the bag where they are, it's somewhere around but quick search around my workshop turned out everything else that I have missed but the sabots.
Come spring and we will continue testing with new and interesting stuff.

Marko

[rsterne]

Ahhhhhh.... the Helium explains a LOT, short barrel though at 21.3"!.... I'll look forward to the weight of the sabot, this will be an invaluable data point for perfecting Lloyd's spreadsheet, IMO....

Bob

[CapArms]

Has anybody done CFD analysis of shock wave formation or choked flow conditions at modern airgun pressures?

[rsterne]

If you have such information, please feel free to share it....

Bob

[Scotchmo]

Has anybody done CFD analysis of shock wave formation or choked flow conditions at modern airgun pressures?

Choked flow is a “standing shock wave” at the port that restricts flow from going above sonic. What are you trying to find out from a CFD analysis?

[CapArms]

Has anybody done CFD analysis of shock wave formation or choked flow conditions at modern airgun pressures?

Choked flow is a “standing shock wave” at the port that restricts flow from going above sonic. What are you trying to find out from a CFD analysis?

   I was figuring that iterative CFD analysis and redesign would enable one to eliminate Choked Flow and standing Shockwaves.  Often these phenomena are so counter intuitive and complex that Computational Fluid Dynamics are the only way to "see" what is happening inside the flow passageways. 

[Scotchmo]

Has anybody done CFD analysis of shock wave formation or choked flow conditions at modern airgun pressures?

Choked flow is a “standing shock wave” at the port that restricts flow from going above sonic. What are you trying to find out from a CFD analysis?

   I was figuring that iterative CFD analysis and redesign would enable one to eliminate Choked Flow and standing Shockwaves.  Often these phenomena are so counter intuitive and complex that Computational Fluid Dynamics are the only way to "see" what is happening inside the flow passageways. 

For a given pressure, maximum flux occurs at Mach 1. Choked flow simply means that we are at that maximum throughput. Besides removing any constrictions, there is nothing to redesign. There’s no way around it.