Analysis of Oblique Shock at RDE Exit Using Tomographically Reconstructed Density Fields

Oblique shock interactions with the nearfield ambient at the exit of a Rotating Detonation Engine (RDE) are investigated. The study employs Rainbow Schlieren Deflectometry (RSD) to visualize and quantify optical ray deflections. Then, deflectometric tomography is used to reconstruct local 3D density fields in the exhaust flow. Experiments are performed in a methane-fueled annular RDE with oxygen-enriched air (2/3 O2 and 1/3 N2 by mole) at a mass flow rate of 0.45 kg/s and equivalence ratio, ϕ = 1. High-speed RSD images are acquired at 581.25 kHz and an exposure time of 369 ns to minimize smearing. The RDE operates in a 6.7 kHz single-wave mode, providing approximately 86 images per wave cycle. These images are used to assess flow structures qualitatively and to create time-resolved local 3D density fields for each cycle. RSD images and reconstructed fields enable isolation of the oblique shock wave, the separation between the hot products and the cold ambient air, and a high-density spiral structure originating from shock-boundary interaction. Results provide a quantitative analysis of the inherently non-uniform, transient RDE exit flow and help explain its nearfield behavior.