Channel Wall Nozzle Research Articles

Technology advancements for channel wall nozzle manufacturing in liquid rocket engines

A regeneratively-cooled or dump-cooled nozzle is a critical component for expansion of hot gases to enable high temperature and performance in liquid rocket engines systems. Regeneratively-cooled channel wall nozzles are a design solution used across the propulsion industry as a simplified method to fabricate the nozzle structure with internal coolant passages. The scale and complexity of the channel wall nozzle (CWN) design can be challenging to fabricate which results in extended lead times and higher costs. Some of these challenges include: 1) Unique and high temperature materials, 2) Tight tolerances on large parts during manufacturing and assembly to contain high pressure propellants, 3) Thin-walled features to maintain adequate wall temperatures, and 4) Unique manufacturing process operations and complex tooling. The United States (U.S.) National Aeronautics and Space Administration (NASA) and U.S. specialty manufacturing vendors are maturing modern fabrication techniques to reduce complexity and decrease costs associated with channel wall nozzle manufacturing technology. Additive Manufacturing (AM) is one of the key technology advancements under evaluation for channel wall nozzles. Much of additive manufacturing for propulsion components has focused on laser powder bed fusion (L-PBF), but the scale is not yet feasible for application to large scale nozzles. NASA is evolving directed energy deposition (DED) techniques for nozzles including arc-based deposition, blown powder deposition, and Laser Wire Direct Closeout (LWDC). There are different approaches being considered for fabrication of the nozzle, and each of these DED processes offer unique process steps for rapid fabrication. The arc-based and blown powder deposition techniques are used for the forming of the CWN liner. A variety of materials are being demonstrated including Inconel 625, Haynes 230, JBK-75, and NASA HR-1. The blown powder DED process is also being demonstrated for forming an integral channel nozzle in a single operation in similar materials. The LWDC process is a method for closing out the channels within the liner and forming the structural jacket using a localized laser wire deposition technique. Identical materials mentioned above have been used for this process in addition to bimetallic closeout (C-18150–SS347, and C-18150–Inconel 625). NASA has completed process development, material characterization, and hot-fire testing on a variety of these channel wall nozzle fabrication technique. This publication presents an overview of the various channel wall nozzle manufacturing processes and materials under evaluation including results from the hot-fire testing. Future development and technology focus areas is also discussed relative to channel wall nozzle manufacturing.

Thermal-structural response and low-cycle fatigue damage of channel wall nozzle

To investigate the thermo-mechanical response of channel wall nozzle under cyclic working loads, the finite volume fluid-thermal coupling calculation method and the finite element thermal-structural coupling analysis technique are applied. In combination with the material low-cycle fatigue behavior, the modified continuous damage model on the basics of local strain approach is adopted to analyze the fatigue damage distribution and accumulation with increasing nozzle work cycles. Simulation results have shown that the variation of the non-uniform temperature distribution of channel wall nozzle during cyclic work plays a significant role in the thermal-structural response by altering the material properties; the thermal–mechanical loads interaction results in serious deformation mainly in the front region of slotted liner. In particular, the maximal cyclic strains appear in the intersecting regions of liner gas side wall and symmetric planes of channel and rib, where the fatigue failure takes place initially; with the increase in nozzle work cycles, the residual plastic strain accumulates linearly, and the strain amplitude and increment in each work cycle are separately equal, but the fatigue damage grows up nonlinearly. As a result, a simplified nonlinear damage accumulation approach has been suggested to estimate the fatigue service life of channel wall nozzle. The predicted node life is obviously conservative to the Miner’s life. In addition, several workable methods have also been proposed to improve the channel wall nozzle durability.