Jon-
SSME preburners had a similar arrangement iirc. It's very common in gas
turbine augmentors/nozzles where it's referred to as a liner
On Dec 31, 2015, at 1:15 PM, Jonathan Goff <jongoff@xxxxxxxxx> wrote:
Henry,
On Thu, Dec 31, 2015 at 1:37 PM, Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Thu, 31 Dec 2015, Richard Garcia wrote:
Of course, the ways to fend off hot gas, like film cooling, all come at a
price; it may be worth it.
Most LPREs have film cooling, and my previous comments where made assuming
there would be at least some film cooling involved.
I prefer to observe a distinction of terminology: the usual (although not
quite universal) practice of adjusting the injector design to put a
fuel-rich layer near the wall is "curtain cooling", while "film cooling" is
reserved for concepts that put a low-velocity *liquid* layer on the wall,
typically by angled orifices in the wall itself (e.g., the V-2 engine did
this).
Duct cooling is also an interesting approach worth considering for high
lifetime engines. Basic idea is you put a very thin-wall cylindrical sleeve
inside the straight part of the combustion chamber with a thin gap between it
and the chamber wall. You run your film coolant behind that duct, and there's
a gap at the bottom where the liquid escapes the duct into the chamber just
upstream of the converging section of the nozzle. The duct doesn't see much
stress because it isn't in contact with the actual chamber wall, and it isn't
constrained from thermally expanding axially. The duct can be made of high
temperature materials like Inconel, and can be allowed to get nice and roasty
toasty, because it isn't really load bearing. The duct keeps the coolant flow
intact further into the engine, and if done right can eliminate the need for
most cooling on the engine with a fairly low overall flow. Not sure how it
trades versus other concepts but it's an intriguing one that I don't know if
it has been used operationally yet. It's also been several years since I've
looked at duct cooling, so I might be mis-explaining it.
P&W's SSME proposal used transpiration cooling
It's my understanding that transpiration cooling, while successful in a
laboratory setting, ultimately proved to difficult to build flight weight
versions that was reliable enough.
It has problems, both passage clogging and flow instabilities, but people
have made it work. If memory serves, P&W had used it extensively in an
experimental high-pressure engine, and thought it entirely feasible for the
SSME. Reportedly, MSFC dismissed it as unworkable without paying any
attention to the details of the P&W experience.
Also, if you need an even flow distributed across the face, a foam-like
surface might not be your only approach. I can think of a few ways of doing
things that could be very clog resistant while still metering the fluids
effectively, which are possible with only somewhat exotic manufacturing
processes...
Beware of assuming that the design space has been thoroughly explored --
often it hasn't! There is a particular problem with people trying something
once, having trouble, and concluding that the whole idea is infeasible.
Along similar lines, quite by chance today I ran across NASA CR-185257, aka
AIAA 90-2116, Quentmeyer, "Rocket Combustion Chamber Life-Enhancing Design
Concepts", which discusses half a dozen different concepts for making
channel-wall chambers more durable. Some seem like long shots, some look
workable.
(Sorry, don't have a URL for that because I ran across it in my own files,
but it ought to be findable...)
Here's a link:
http://ntrs.nasa.gov/search.jsp?R=19900015867
~Jon