Analyzing Simulations of Flameholder Cavity Designs to Prevent Unstart in Scramjet Engines — 51a — Mckenna DuFrene, Dr. Jung-Han Kimn

Flameholder cavities are an essential part of scramjet engines. They provide extra  time for air and fuel to mix, which creates a more reliable air-breathing engine. However,  with the volatile nature of internal supersonic airflow, the design of the flameholder cavity is  important for managing the back pressure at the engine’s outlet to avoid unstart: a  phenomenon at the inlet of the engine that restricts the delivery of oxygen to the combustion  section. Excessive amounts of back pressure or strong shockwave interactions with the  boundary layer can cause unstart. The shape of the flameholder cavity affects these  components, so five cases were simulated in StarCCM+ using Reynolds Averaged Navier  Stokes (RANS) model, specifically the SST turbulence model. The first case was the  accepted shape for scramjet engines – a rectangular cavity with a ramp leading out of it  toward the outlet. The next four cases were compared to the original: a rectangular-shaped  cavity with no ramp, a circular-shaped cavity, and two triangular-shaped cavities with  different depths. In each of the cases including the original, the residuals spiked multiple  times, and back pressure was evident in the scalar scenes. The circular-shaped cavity had  the most stable results along with the rectangular cavity with no ramp. Knowing which cavity  geometries will positively affect airflow in scramjet engines will lead to less risk of unstart.

South Dakota State University
Dr. Jeffery Doom