We did that on our 10k engine. The boilerplate chamber (just made of
mild steel because the instabilities occurred after about 0.5 sec, so no
need to destroy an expensive regen cooled chamber) was equipped with 3
very fast pressure sensors on its perimeter. We choose the positions and
their angles in a way, that we were able to draw conclusions on the
amplitude and phase of the oscillation. The chamber also had 3
additional ports (radial, tangential and almost longitudinal) where a
device could be mounted which was able to trigger a corresponding
instability mode. That device can be charged with a 9mm round (no bullet
of course) which was triggered by a pin actuated by a coil driven by a
400V capacitor. Between the round and the chamber was some kind of burst
disk.
Bruno
"At that time [1909] the chief engineer was almost always the chief test
pilot as well. That had the fortunate result of eliminating poor
engineering early in aviation" (Igor Sikorsky)
--
Bruno Berger
Swiss Propulsion Laboratory
E-Mail: bruno.berger@xxxxxx (HTML-Mails will be dropped!)
PGP: http://www.spl.ch/contact/Bruno.Berger.asc
WWW: http://www.spl.ch
HAM: HB9RSU
Am 04.01.2016 um 03:35 schrieb Henry Vanderbilt:
NASA does like to test stability by setting off a small charge of RDX
fast high explosive inside an operating chamber, then recording the
results with multiple high-bandwidth chamber pressure sensors. The
detonation essentially pulses the chamber across a very wide range of
frequencies, and the data of interest is how fast the ringing then damps
out. If it does damp out, of course. If instead some frequency builds
up and runs away, well, your engine definitely flunked.
