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25 Years of Nailing Sonic Choking Calculations

Applied Flow Technology
AFT Arrow 25yr flow analysis software

25 Years of Nailing Sonic Choking Calculations

Applied Flow Technology’s compressible flow analysis software,  AFT Arrow, celebrated its 25th anniversary this Fall. Shortly after leaving his job as an Aerospace Engineer in 1994, AFT Founder and President, Trey Walters, P.E., began developing flow analysis software in his basement. He first developed AFT Fathom and AFT Impulse, AFT Arrow came soon after to complete the circle. Looking back at it’s 25 years, AFT Arrow continues time and again to show itself to be head and shoulders above other software out there claiming to do compressible flow.

While AFT Fathom was AFT’s first software product, and AFT Impulse is AFT’s most complicated, both of those products essentially use textbook methods for pipe network calculations. For AFT Fathom, the textbook was Jeppson’s Analysis of Flow in Pipe Networks and for AFT Impulse the textbook was Wylie and Streeter’s Fluid Transients in Systems.

For AFT Arrow the textbook for single-pipe calculation methods was Saad’s Compressible Fluid Flow.

However, there was (and still is) no textbook for compressible flow in pipe networks.

Walters did not want to settle for a simplified ideal-gas, adiabatic-type of solution methodology to which other software companies have resorted. He wanted the whole thing – heat transfer, real gas modeling and fully capable sonically choked modeling capability. This took considerable effort and research. Eventually he would adapt Saad’s single-pipe compressible flow methods and Jeppson’s network methods for incompressible flow into a completely new calculation technique. Then, he and Jeff Olsen, AFT’s V.P. Technology, threw in some novel iterative approaches to handle special cases of sonic choking.

In the end AFT Arrow was commercially released in October 1995. Orders surged immediately.

You can read more about AFT Arrows development in Walter’s blog “AFT Arrow Turns 20 This Month-the Behind the Scenes Story.”

You may be wondering why a gas flow software is called AFT Arrow.

The software was almost called “Stratus”. But then a moment of fate intervened.

Walters was working heavy hours in those days and his wife decided to take their young children to visit grandparents. He took his family to the airport and on the way back home, he passed an RV on the highway. The brand of the RV was displayed in large letters on its back – “Arrow”. And like an arrow which pierced him from out of the blue, he immediately realized AFT’s second product would be called “AFT Arrow”.

At AFT we like to say AFT Arrow has a “special sauce” that makes it the most dependable and trustworthy compressible flow analysis tool. It has nailed sonic choking calculations now for over two decades and is going strong.

For more information about AFT Arrow, visit:

Sources: AFT Arrow is 25 Years Old…and Still Going Strong Where Did the Name “Arrow” Come From?

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