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Minimizing hydraulic losses in additively-manufactured swirl coaxial rocket injectors via analysis-driven design methods

  • Author(s): Morrow, David
  • Advisor(s): Spearrin, Raymond M
  • et al.

Additive manufacturing (AM) has matured significantly over the past decade and become a highly attractive tool for reducing manufacturing complexity and removing traditional design constraints. This is particularly desirable for rocket combustion devices which often feature hundreds of individual parts with precise tolerances. The degree to which AM can be used to improve combustion device performance, however, has been less rigorously explored. In this work, hydraulic performance impacts associated with and enabled by AM are assessed for a liquid bi-propellant swirl coaxial injector. Specifically, a single-element liquid oxygen/kerosene injector based on a canonical design was manufactured from inconel using Direct Metal Laser Sintering at two different coaxial recess depths. Cold-flow testing for the as-manufactured baseline injector found a reduction in the designed discharge coefficients, which is primarily attributed to increased surface roughness inherent in the AM process. Quantifying this difference provides data for tuning surface roughness effects in Computational Fluid Dynamics (CFD) models, which may be used to inform the design stage. In addition, CFD simulations were leveraged to identify hydraulic losses in the baseline design and redesign a more hydraulically efficient injector geometry utilizing reductions in dramatic flow constrictions. For the modified injector geometry, computational results predict a 19% and 8% increase in the fuel and oxidizer discharge coefficients, respectively, as well as an 18% increase in angular momentum relative to the baseline. These results in addition to recommendations made for minimizing frictional losses that resulted from the printing process demonstrate how AM and analysis-driven design may be utilized to develop a more hydraulically efficient liquid rocket engine injector, thus highlighting a pathway to higher thrust-to-weight ratio propulsion systems and increased launch vehicle payload capacity. This work was presented in part at the 2019 AIAA Propulsion and Energy Conference.

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