Orbiter-Forum Calculation of Tubular-wall thrust chamber
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 07-10-2012, 02:45 PM #1 Phil Smith Orbinaut Calculation of Tubular-wall thrust chamber When I've been started to design thrust chamber one question appeared. As you know tubular wall has different cross-sections along the chamber length. So how I can calculate tube dims at any section of chamber? In the beginning we have some parameters: number of tubes - 166; outside tube diameter (at combustion chamber) - 5.00 mm; tube wall thickness - 0.5 mm; Combustion chamber dia - 260 mm; Throat dia - 135 mm; Nozzle exit dia - 530 mm. Here's a little sketches for easier understanding what i mean: 1. basic thrust chamber internal layout with all dims: 2. Cross-sections of the tube (A-A - combustion chamber, B-B - Throat, C-C - Nozzle exit): So X and Y dims are problem. I know they depends on chamber radius, but what formula? Appreciate any help! PS all dimensions are in MM Last edited by Phil Smith; 07-10-2012 at 02:50 PM.
 07-10-2012, 08:26 PM #2 Notebook Orbinaut I've always assumed the tubes were constant section, are you getting this from a specific engine? One engine I've took an interest in is the Rolls-Royce RZ20, a copy of the Rocketdyne S3, about 1950 and frozen to death. Have some pictures and info on that: http://i89.photobucket.com/albums/k2...4/File0046.jpg This drawing shows a cutaway of the fuel circulating tubes: http://i89.photobucket.com/albums/k2...4/File0045.jpg Note the legend "Fuel Cooled Tubular Wall", though if you zoom in to the top of the tubes, it looks like a rectangular cross section. That may just be the join to the top manifold? Finallly, our dear leader showing enormous enthusiasm for the UK 1950's rocket programme(note tame flunky with watch) http://i89.photobucket.com/albums/k2...4/File0047.jpg Not that I'm bitter or twisted or anything. n.
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 07-10-2012, 08:48 PM #3 kuddel Donator Quote: Originally Posted by Notebook  This drawing shows a cutaway of the fuel circulating tubes: http://i89.photobucket.com/albums/k2...4/File0045.jpg Note the legend "Fuel Cooled Tubular Wall", though if you zoom in to the top of the tubes, it looks like a rectangular cross section. That may just be the join to the top manifold? Hi there, this video is from a (great) german kids-educational-show, but shows the manufactuing of a Ariane-V (Vulcain) engine in the best way I have seen so far: The "cooler tubular wall" creation starts at about 04:00... From that you can see, that it is definitely not circular tubes, but 'flat' ones, due to the milling process. /Kuddel Last edited by kuddel; 07-10-2012 at 08:55 PM.
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 07-10-2012, 09:00 PM #4 Notebook Orbinaut Yes, things have moved on a bit... excellent video, don't get the lingo, but the pictures tell it. N.
 07-11-2012, 08:11 AM #5 Phil Smith Orbinaut Quote: Originally Posted by Notebook  I've always assumed the tubes were constant section, are you getting this from a specific engine? I'm getting that from my own engine project and I can share with calculations if you wanna. So here I took scan from one of my favorite book "Modern Engineering for Design of Liquid Propellant Rocket Engines" by Dieter K. Huzel and David H. Huang: As you see on fig. 4-36 tube cross-sections are show. So I wanna know how precisely calculate section dimensions. Quote: Originally Posted by Notebook  One engine I've took an interest in is the Rolls-Royce RZ20, a copy of the Rocketdyne S3, about 1950 and frozen to death. Have some pictures and info on that: oh, I know that engine too. I've read some books (amerecan and russian) and that engine was common example of tubular-wall thrust chamber structure Quote: Originally Posted by kuddel  The "cooler tubular wall" creation starts at about 04:00... From that you can see, that it is definitely not circular tubes, but 'flat' ones, due to the milling process. Oh man great video! Thanks! I know there are several ways to organize regenerative cooling chamber. Two of them - tubular wall and wall with channels (just like on your video):
 07-11-2012, 08:32 AM #6 C3PO Donator Wouldn't the correct formula be a simple circumference calculation? If you simplify it to calculate rectangular tubes with "tall" tubes in the narrow parts and "flat" ones near the rim, the formula should be easy.
 07-11-2012, 08:48 AM #7 Notebook Orbinaut What C3PO said. I'm right behind him... N.
 07-11-2012, 09:07 AM #8 Phil Smith Orbinaut I did this calculus yesterday. Here's result (smth like that?): i thought it's quite simple to be precise. Last edited by Phil Smith; 07-11-2012 at 09:09 AM.
 07-11-2012, 09:17 AM #9 Notebook Orbinaut where are you getting the i subscript from? N.
 07-11-2012, 09:20 AM #10 Phil Smith Orbinaut Quote: Originally Posted by Notebook  where are you getting the i subscript from? N. "i" is any section of chamber. the pic is screenshot from MS Word. Last edited by Phil Smith; 07-11-2012 at 09:23 AM.
 07-11-2012, 10:17 AM #11 Notebook Orbinaut Let me get this right...could take some time. From your post #1 above, you are after how x and y change from the top of the engine to the bottom? You have a cylindrical cross-section near the top(a), and two rectangular sections at two points (b) and (c). So a formula that defines the cross-section as you travel down from the top of the engine? N.
 07-11-2012, 03:34 PM #12 Phil Smith Orbinaut Quote: Originally Posted by Notebook  Let me get this right...could take some time. From your post #1 above, you are after how x and y change from the top of the engine to the bottom? You have a cylindrical cross-section near the top(a), and two rectangular sections at two points (b) and (c). So a formula that defines the cross-section as you travel down from the top of the engine? N. I know just circumference calculation. I depends on radius of the chamber because you need to fit constant number of tubes in different circle length. In reality there's no ideal rectangular shape if tube was cylindrical - after forming tube reminds something like rectangular with round corners (like on FIG 4-36 I've posted above). But I think there is much more sophisticated formula and I wanna know it too.
 07-11-2012, 03:49 PM #13 Notebook Orbinaut Yes, I forgot about the constant number of tubes, that makes it fun. It rang a bell with me as I was trying to make a hi-res model of the RZ-2 engine in 3ds Max. Tried to extrude a circle along a path, then make an array of the result. Sort of worked, but it needs a bit of attention... Not sure you will get a formula for this, might need an itterative solution? N.
 07-11-2012, 04:57 PM #14 Phil Smith Orbinaut Quote: Originally Posted by Notebook  Yes, I forgot about the constant number of tubes, that makes it fun. It rang a bell with me as I was trying to make a hi-res model of the RZ-2 engine in 3ds Max. Tried to extrude a circle along a path, then make an array of the result. Sort of worked, but it needs a bit of attention... Not sure you will get a formula for this, might need an iterative solution? N. I'll calculate sections with method I've written before and check results in autodesk Inventor (software just like 3d max but for mechanical). And when you form cross-section there's one more primary rule - section area is constant too. PS It will good to see your work - if you'll have any question about rocket engines - let me know Last edited by Phil Smith; 07-11-2012 at 05:08 PM.
 07-11-2012, 05:20 PM #15 Notebook Orbinaut Nothing worth showing regarding engines yet, I have problems with clipping when I try to do cm scale stuff in Max. Maybe because its an old version 5.1, but I'm not going to upgrade now, can't justify it. Orbiter wise, I'm stuck with my Westcott upgrade, usual C++ headbanging, but I'll keep at it: http://i89.photobucket.com/albums/k2..._Orbiter_1.jpg Having a break from that now, and doing a base, at least I know I can finish that! N.

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