Zac:
Have you considered a hand calculation?
Sutton's liquid rocket engine example shows how--although I expect you
understand that part. So doing, or even setting up a simple spreadsheet, will
let you know what you should expect from your simulation. For a test engine,
checking heat transfer at the chamber wall, the throat, and the exit is
probably more than sufficient; no simulation required.
In any case, 20% BLC should be plenty: I once saw a 5000 lbf. stainless engine
do two 2.5 minute runs on the same day--pausing only to refill the tanks--using
nothing but BLC. It was pristine after the second run.
I have often thought were I ever to build another liquid, I'd just spin the TCA
from minimum gage stainless tube and carry 20% more fuel: it's net way cheaper
than even an ablative TCA. I'd also look hard at hydrogen before falling back
to methane.
Bill
Sent from my iPhone
On Jun 27, 2017, at 12:42 PM, Zachary Martinez <znm3m8@xxxxxxx> wrote:
Yes I understand that part. I was always assuming that the film was
transparent to the radiation. What I am trying to do is different from that.
Say radiation heat flux is 500kw/m^2 on the inner wall of the chamber.
Nothing I do can change that number. This effect alone makes the inner
surface in steady state conditions unbearably hot. The only way to reduce
inner wall temperature is a) reduce the wall thickness so and get rid of the
heat using radiation and natural convection on the outer surface or b)
actually transfer heat from the inner wall to the cooler film. As our engine
has a couple SAE ORB ports on the side for pressure measurement reducing the
wall thickness makes manufacturing more complex so we were trying to go with
option b and simulate this somehow.
Zachary Martinez
Aerospace & Mechanical Engineering
Missouri S&T
On Tue, Jun 27, 2017 at 1:34 PM, Alexander Ponomarenko <contact@xxxxxxx>
wrote:
Hi,
Indeed, within thermal analysis in RPA it is supposed that the liquid film
is fully transparent for radiation (that is, the it is using the temperature
and the properties of the wall to calculate the radiation heat transfer).
Still, you may affect the value of radiation heat transfer by adjusting the
value of "Emissivity of gas-side wall surface" (default is 0.8) on the tab
"Heat Transfer Parameters". By reducing this value, you may simulate the
lower transparency of the film. Of course, such approach won't consider
heating of the film from absorption of some part of radiation energy. And
you have to find the reasonable value surface emissivity on your own.
Regards,
Alexander
On 06/27/2017 08:17 PM, Zachary Martinez wrote:
Good Afternoon,
Does anyone have experience in analyzing the the thermals of an engine that
only uses film cooling (ie no regenerative or ablative). I was trying to
simulate this using RPA but was coming up with strange effects.
It seems that in RPA if you set up a film cooling section it calculates the
convective heat transfer from the film to the wall independently from the
radiation heat transfer from the hot core. When I adjust the film cooling
parameters I can get the convective heat transfer to the wall to be 0 W/m^w
in sections (ie. fully insulated). However because the radiation
heat transfer is calculated separately I am getting a steady state inner
wall temperatures in excess of 1000K which is far beyond the melting point
of aluminum. This means even if I simulate the engine with over 50% film
cooling I can't get a steady state solution that is feasible.
Are there any tools that I could use to simulate this heat transfer problem
where the convective heat transfer is negative (ie the film is actually
cooling the chamber). I know some on this list have developed engines that
can run steady state using only film cooling, how did you do it?
Thank you,
Zachary Martinez
Aerospace & Mechanical Engineering
Missouri S&T
