I'm also interested in references on relative water massflows to sound damping.
In the interim, you should google Swiss Propulsion Labs and see how
the clever folks there built a sound reducing liquid test stand.
On Sat, Nov 19, 2016 at 5:20 PM, Graham Sortino
<dmarc-noreply@xxxxxxxxxxxxx> wrote:
Apologies for all of the questions on this... I live in the North East so
inevitably I think noise is going to be a significant factor for wherever we
find to test.
I was just re-reading this post:
http://yarchive.net/space/rocket/rocket_noise.html and I noticed it
mentioned that it mentioned using water-spray systems to (presumably) dampen
the sound by injecting water into the exhaust stream. Does anyone have any
references on how to determine the volume of water needed and how much it
could dampen the sound?
Also, I was also a bit curious to see if anyone has kept metrics on the
sound volume (or knows a good source) for relatively small rocket engines.
The size of our engine would be 500 lbf initially and would not be larger
than 5000 lbf eventually. If not I think I will add this as something to
measure for our eventual tests.
Thanks again very much for the advice.
Graham
________________________________
From: Wyatt Rehder <wyatt.rehder@xxxxxxxxx>
To: arocket@xxxxxxxxxxxxx
Sent: Wednesday, November 16, 2016 12:55 AM
Subject: [AR] Re: Rocket Test Location Requirements
1. The keywords you are looking for is "Explosive Quantity Safety
Distance" Here is a NASA manual on how to cite for rocket propellants
specifically: https://www.hq.nasa.gov/office/codeq/doctree/NASASTD871912.pdf
I haven't personally worked through that manual, but at a cursory
glance it looked good. Also beyond just explosive quantity, in the
event of a hard start you should assume major pieces of your engine
can go several hundred yards at high rates of speed.
2. From the Arocket Archives:
http://yarchive.net/space/rocket/rocket_noise.html
There is also probably a handful of technical papers on the subject
I'm sure as well.
3. You should pick on how your want to configure your test stand based
on two things. First what is the weather is like where you are
testing, and second how far away your shop is from your test stand.
If it rains/snows frequently or its windy all the time a partially
enclosed test stand is a good idea. Keeps your electronics protected
and keep the people working on it happier (most of the time). Downside
is it makes it more difficult to work on, or in an off nominal case it
is harder/more dangerous to access something that is on misbehaving,
and you are more restricted in your ability to run away if things are
really bad.
Copenhagen gets away with using a shipping container because their
test stand is pretty much behind their workshop. If you are going to a
remote gravel pit 40 minutes away from town you probibly do not want
your equipment static. For one things are more exposed to the
elements, two you will be making several hundred trips to the hardware
store for forgotten/broken widget A or missing tool B. If you are in
your workshop that makes this process much easier. That's why most use
mobile test stands mounted to trailers since it lets you work on it
and prep things from the comfort of a garage. If your weather is
crappy use a enclosed trailer.
Using kerosene it isn't that likely for you to get explosive vapor
buildup unless it is being atomized. But this is a real concern in
certain instances so proper ventilation is something that should be
thought of depending on your fuel. Acoustics wise the loudest part is
downstream of the nozzle, upstream and to the side of the engine it
isn't nearly as loud. So it likely won't prove to be that bad of an
issue.
4. You have a bit of more trouble with kerosene being your fuel as
water isn't as helpful for putting it out. Alcohol is great since it
is very soluble in water so you just dump water on it and easily put
it out. Use a CO2 extinguisher for small fires, this minimizes the
damage to your test stand. For big fires I'm not really that well
versed in firefighting techniques. You are a pretty small engine so
your fires aren't going to be "That" big. I know foam is one of the
approved firefighting methods for petroleum fires. You could also have
a gas powered pump feeding from nearby pond and have nozzles pointing
at your test stand. You could use the water as sound suppression
during normal runs and have a remote manual valve to redirect towards
your test stand for large fires. This would at least get the fire off
of your stand (but move it elsewhere). I would deferr to other's ideas
on firefighting techniques. At the very least I would not go with an
automated system. That is greatly adding to cost, complexity, and
asking for an accidental activation. Automated is good when the fire
hazard is present when no one is there. Since any time there is a fire
hazard you will be actively monitoring it a automatic system doesn't
have as many benefits.
5. You either use concrete or metal for anything LOX is happening
over. Never do anything over asphalt (LOX + Asphalt = Shock sensitive
explosive). I'm not sure what the guidelines about gravel or dirt are.
Definitely don't be around anything flammable like grass or leaves.
On Tue, Nov 15, 2016 at 5:40 PM, Graham Sortino
<dmarc-noreply@xxxxxxxxxxxxx> wrote:
Hi All -
We are currently looking for a suitable location to test our to be
developed
500 lbf LOX/Kerosene pressure fed engine and I was wondering if I could
ask
a few questions regarding what to look for in a test site:
Is there a rough calculation to determine the size of the explosion that
would occur in the event of a hard start given the engine size and
propellants (eg. 500 LBF LOX/Kerosene)? I'd like to use this to ensure
that
the test location has sufficient space in the event of an accident.
Is it possible to roughly estimate the decibel level of sound produced by
a
test stand engine firing horizontally. Basically, I’d like to have a way
to
ensure that whatever location we test at will not generate too much noise
for anyone in the near area. I realize this depends on how far the sound
is
able to travel as well but getting a general idea of decibel levels would
help us figure this out.
We were thinking of using a shipping container to test the engine from.
The
container would be open on at least one side with the divergent part of
the
nozzle pointing out towards the open side. We had the idea from a recent
Copenhagen Suborbital test:
https://www.youtube.com/watch?v=K61xY_v84mE&feature=youtu.be. It offers
the
benefit of having a semi-permanent place to keep the test stand, it can be
secured while not in use, would help limit damage if there was a
spontaneous
disassembly. Where I’m a bit concerned is the amount of vibration, noise
and
things bouncing back and forth off the walls as well as any potentially
explosive gas mixtures getting trapped in the container. Also, I’m a bit
on
the fence as to whether this would make any propellant spills (a) easier
to
cleanup since they would be on the floor of the container or (b) more
dangerous because it would pool inside the container.
In the event there is a fire I’m trying to figure out the best way to
extinguish it. Would an automated suppression system (eg. some sort of
sprinkler inside the crate) or is it enough to have a powerful house or...
is it better to just let it burn out considering the difficulties of an
oxygen enriched environment. In other words what level of equipment would
need to be on hand.
I'm assuming concrete is a good surface for a test on in case of any
propellant spills.
Other points to consider?
Many thanks as always for your advice.
Kind Regards,
Graham
