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Why does the YF-75D nozzle material have such a strong spiral pattern?

Is it a result/biproduct of a manufacturing process only, or does it have some specific function?

edit: The last, cropped images that have enhanced contrast and sharpening show a bead-like appearance around the bottom edge of the nozzle. This gives the impression that the nozzles is fabricated from fused rods or "ropes" of metal. This is consistent with them being nearly vertical at the top, and increasingly spiraled as the bell shape widens.

Could these have been made by some additive process?

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above: YF-75D engine cropped from here.

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above: YF-75D engine cropped from Chinaspaceflight. (In Chinese)

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above: YF-75D engine from Chinaspaceflight. (In Chinese)

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above: YF-75D engine nozzle detail, cropped from Chinaspaceflight. (In Chinese)

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    $\begingroup$ @OrganicMarble possibly, but the pitch seems to coarse to me. Look up at the top where it mounts to the engine - those lines are almost vertical. I'm thinking it's an additive process like making a clay pot from ropes of clay, but I still don't know why it would look like this. $\endgroup$ – uhoh Nov 4 '16 at 13:26
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    $\begingroup$ This engine uses the expander cycle, so propellant is circulated through the nozzle walls. Could be you're looking at tubes brazed together. $\endgroup$ – Hobbes Nov 4 '16 at 17:42
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    $\begingroup$ @Puffin agree, there appear to be none of the usual ducts to supply or return coolant from the nozzle extension. This looks like a radiation cooled nozzle extension to me. $\endgroup$ – Organic Marble Nov 6 '16 at 13:35
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    $\begingroup$ @uhoh Google translate suggests coolant going through 242 spiral tubes embedded in nozzle and then being dumped through 726 "micro-nozzles". Also from this asi.org/adb/04/03/09/01/sep-engines.html "Cooling Method: hydrogen is heated to 150K during cooling of combustion chamber wall along 128 longitudinal channels for injection in gaseous form. The nozzle cooling system employs 242 helical tubes; 0.15 kg/s of hydrogen is dumped overboard." $\endgroup$ – Ohsin Jun 18 '17 at 17:29
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    $\begingroup$ @uhoh More information from translated text here bernd-leitenberger.de/ariane4.shtml "The nozzle consists of 242 individual tubes from Incotel 600, which are helically welded together. The nozzle is cooled by 150 g of hydrogen / second. The temperatures reach a maximum of 1080 K at the nozzle neck. While the hydrogen of the combustion chamber cooling is combusted with the remaining hydrogen, the hydrogen that cools the nozzle is exhausted at its end through the open tubes. This creates a small extra thrust." $\endgroup$ – Ohsin Jun 18 '17 at 17:56

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