Design and testing of an additively manufactured flameholder for scramjet flows

Abstract

A small-scale cavity flameholder for high-speed, premixed ethylene combustion has been designed, additively manufactured, and tested at Mach 5 enthalpy. The work has enabled a comprehensive study on the effects of flow compressibility and heat release on turbulent flame structures and stabilization mechanisms. The cavity is sized to produce a practical computational domain for Direct Numerical Simulations. Likewise, the flameholder is supported away from the flow path walls to minimize boundary layer growth upstream and simplify the numerical calculations. Optical access is provided for laser diagnostics. Challenges related to transforming a direct-connect combustor flow path into a semi-free jet flow path for immersed models were encountered, primarily flow blockage and heat removal. The final design can sustain an ethylene flame for repeated cycles lasting more than an hour. The flameholder was fabricated from Inconel 718 with internal cooling passages incorporated throughout. This paper presents a methodology for design and fabrication of additively manufactured scramjet combustor components and documents the first published conversion of a direct-connect, high-speed combustion wind tunnel to a semi-free jet configuration. While additive manufacturing enables novel designs with complex geometries, residual stresses and geometric distortion are notable concerns that must be considered in the design stages.