---------- Forwarded message ----------
From: *Richard Nakka* <richard.rocketry@xxxxxxxxx>
Date: Wednesday, April 5, 2023
Subject: [sugpro] SRM_2023
To: sugpro@xxxxxxxxxxxxx
Greetings...!
SRM has been updated:
https://www.nakka-rocketry.net/softw.html#SRM
The main reason for the update is due to an error in my original
calculation of the two-phase isentropic exponent (k_2ph) that is used for
calculation of motor thrust. This incorrect value has been used since 'day
one' of SRM. A sharp-eyed rocketry engineer caught the apparent error on my
website some months ago. We discussed this in detail and it eventually
became clear that he was right. I had inadvertently used molar-based rather
than mass-based units in the calculation of k_2ph. This led me to spend the
next few months totally reviewing all aspects of rocket motor theory as it
relates to two-phase flow. This was taxing on the brain, revisiting my
thermo, compressible fluid flow, calculus, etc, that I had not touched much
of in the past twenty years or so...! But it was worth it, leading to some
neat simplifications with regard to rocket motor theory, and confirming
that SRM has otherwise been proven to be correct in its methodology.
The consequence of the error is, fortunately, quite small, leading to a
3-4% reduction in thrust (and therefore total and specific impulse)
predictions.
Motor chamber pressure is unaffected by this correction.
I took advantage of this opportunity in updating SRM to include KNFR
(fructose-based) and KNPSB propellants.
Richard