AFT Fathom and AFT Arrow Guide Rocket Design at KETEMA: A Retrospective
AFT Arrow™ Case Study
Ketema | Thruster Control System | Aerospace
Unruly analysis by hand, or spreadsheets, is still one of the common
reasons AFT users rely on software. Especially as system complexity
grows with branching networks, heat transfer, and compressibility, it is harder
and harder to be confident in hand calculations or spreadsheet alternatives.
PROBLEM
- Design of reusable and expendable launch vehicles (ELVs) in 1997
- Necessary to model the fluid and thermal systems onboard ELVs
ANALYSIS
- AFT Fathom and Arrow used to model:
–Pressurization Systems
–Nitrogen Attitude Control Systems
–Propellant Feed Systems
SOLUTION
- Found agreement between modeled and collected data within 5%
- Cited ease of use, extensive fluid databases, and component losses as primary software appeal
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Applied Flow Technology celebrated its 25th anniversary in 2019. Over the course of its history, customer-submitted case studies have affirmed the confidence and convenience AFT software enables. This case study was originally written in 1997 and was re-released as a retrospective in 2021.
Problem Explained
You don’t have to be a rocket engineer to use AFT Fathom or AFT Arrow… unless your job is rocket engineering. KETEMA designs systems for re-usable and expendable launch vehicles (ELV’s), today’s formal term for rockets. The design of fluid and thermal aspects of the ELV systems at KETEMA is the responsibility of Ichi Wakabayashi, Senior Mechanical Engineer. He chose AFT Fathom 2 and AFT Arrow 1 to help his group model the many fluid systems aboard an ELV.
Some of the reasons Wakabayashi cited for choosing AFT software were ease of use and the extensive database of fluid properties and component loss coefficients. Since the release of this case study, AFT has implemented three other fluid databases, the Chempak database, NIST REFPROP, and ASME Steam/ Water tables. Both Chempak and NIST REFPROP allow for mixtures and dynamic mixing in Arrow.
Tools and Analysis
“Previously, analyses were done by hand, which was tedious and time consuming”, Ichi said. “AFT [software] allows a repeatable tool for flow analysis that allows faster modeling of systems…with good graphical and tabulated outputs.” Unruly analysis by hand, or more commonly now with spreadsheets, is still one of the common reasons AFT users rely on software. Especially as system complexity grows with branching networks, heat transfer, and compressibility, it is harder and harder to be confident in hand calculations or spreadsheet alternatives.
KETEMA has used Fathom and Arrow on numerous systems including: Pressurization systems, nitrogen attitude control systems, and LO2, RP-1 and Ethanol propellant feed systems. The Arrow 1 model of the gaseous helium pressurant system for propellant tanks is shown in Figure 1, mirrored with the modern Arrow 8 model. It is surprising the file still opens, let alone runs in a version 24 years later. Since 1997, AFT has also added isometric modeling options and other workspace improvements to make it easier to interpret your model.
Solutions & Benefits
KETEMA had opportunity to check the AFT Fathom predictions against test data. AFT Fathom predictions of the rocket engine propellant feed system pressure drop agreed within 5% with data collected during firing tests on an engine test stand. Even 24 years ago AFT software was tested and verified against field data. With the annual Platinum Pipe Award, even more case studies emphasizing result accuracy and data correlation are submitted each year.
With the many aerospace fluid systems encountered at KETEMA, it appears that AFT Fathom and AFT Arrow will be put to good use in the future as well. With such unique piping systems, it is gratifying to see demonstrated AFT software’s flexibility as general purpose pipe flow analyzers.
Figure 1: A side-by-side comparison of the Helium pressurant
system in Arrow 1 and Arrow 8. The resemblance is uncanny